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Unraveling the relative importance of factors driving post-fire regeneration trajectories in non-serotinous Pinus nigra forests
... salzmannii in Spain. These pine species have shown a decrease in post-fire regeneration after high severity fires and in the absence of tree planting, only reestablish in areas close to fire refugia, which act as seed source (Christopoulou et al. 2014;Martín-Alcón and Coll 2016;Chambers et al. 2016). There is widespread concern for post-fire recovery of these foundation species in dry forest settings. ...
... Microclimatic site conditions such as heat load, moisture deficit, soil fertility, and interactions with other species have proven important drivers of seedling regeneration for several species in the Western US (Downing et al. 2020). In the case of P. nigra, post-fire performance also depends on its ability to withstand competition for growing resources from other trees and shrubs or benefit from positive interactions with other species (Christopoulou et al. 2014;Martín-Alcón and Coll 2016). For example, Sánchez-Pinillos et al. (2018) demonstrated important growth reductions in postfire regeneration of this pine due to competition for water from resprouting oak. ...
... Our results indicate that at higher DWD levels, regeneration abundance inside refugia is lower than outside refugia. This trend is only reversed at the lowest DWD levels (minimum DWD: 0 outside refugia and 1.03 inside refugia; Supplementary Fig. 3), where light availability inside refugia may no longer be a limiting factor, and regeneration outside refugia is primarily constrained by seed source distance (Martín-Alcón and Coll 2016). This decline in regeneration inside refugia with increasing DWD aligns with findings for ponderosa pine and Douglas-fir in the USA, where juvenile tree survival and growth were higher in areas with lower canopy cover (Hill et al. 2024). ...
Context
Recent shifts in fire regimes challenge recovery of forest ecosystems. In Catalonia, Spain, the capacity of Pinus nigra to persist has been affected by recent high severity fires.
Objectives
To understand the biophysical conditions that support P. nigra recovery after high severity fire, we investigate the main biophysical drivers—seed availability, community interactions, water, and nutritional constraints—affecting post-fire regeneration patterns in Catalonia.
Methods
We identified fire refugia and calculated the distance-weighted refugia density (DWD) across four fire footprints to represent the seed source abundance. We surveyed abundance of regeneration and shrub cover on 270 sites. We tested identical statistical models for “inside” and “outside” fire refugia, to assess the role of fire refugia and main biophysical drivers on post-fire regeneration.
Results
The DWD had a positive effect on post-fire P. nigra recovery, with a stronger effect outside refugia than inside. Inside fire refugia, canopy trees had a sheltering effect on post-fire regeneration, reducing negative effects of heat load, particularly at higher aridity plots. Presence of Rubus spp. broadleaf shrubs enhanced the abundance of regeneration both inside and outside refugia. Total shrubs cover negatively impacted regeneration inside refugia and sites with greater aridity outside refugia but exerted a facilitative effect on P. nigra regeneration outside of fire refugia at sites with lower heat load.
Conclusions
Seed source abundance is an integral driver of post-fire regeneration however, biophysical site conditions are important filters that amplify or diminish regeneration. This ecological information can be used to tailor post-fire management goals for forest recovery.
... Variability in recovery rates has been shown to depend on the interactive effects of numerous biotic and abiotic factors related to the nature of the fire, life history traits of species, and environmental conditions following fire (Chambers et al., 2016;Johnstone et al., 2016;Stevens-Rumann et al., 2018). For example, post-fire recovery of dry mixed conifer forests in the western US is strongly affected by fire severity (Chappell and Agee, 1996;Meng et al., 2015Meng et al., , 2018Kemp et al., 2016;Harvey et al., 2016;Vanderhoof et al., 2020) and pre-fire condition (Martin-Alcon and Coll, 2016;Zhao et al., 2016). Other factors that can be important in vegetation recovery after fire include vegetation type (Epting and Verbyla, 2005;Yang et al., 2017); site topography, including slope, aspect, and elevation (Wittenberg et al., 2007;Meng et al., 2015;Liu, 2016;Chambers et al., 2016;Haffey et al., 2018); and post-fire climate, including temperature and moisture conditions (Chappell and Agee, 1996;Meng et al., 2015;Stevens-Rumann et al., 2018;Kemp et al., 2019;Guz et al., 2021). ...
... We used partial dependence plots (PDPs) to visualize the influence of each explanatory variable on the degree of recovery of LAI and albedo at 10 and 20 years post-fire. A PDP quantifies the marginal effects of a given variable on an outcome and provides a mechanism to explore insight in big datasets, especially when the random forest is dominated by lower-order interactions (Martin, 2014). ...
Understanding vegetation recovery after fire is critical for predicting vegetation-mediated ecological dynamics in future climates. However, information characterizing vegetation recovery patterns after fire and their determinants over large geographical extents is limited. This study uses Moderate Resolution Imaging Spectroradiometer (MODIS) leaf area index (LAI) and albedo to characterize patterns of post-fire biophysical dynamics across the western United States (US) and further examines the influence of topo-climatic variables on the recovery of LAI and albedo at two different time horizons, 10 and 20 years post-fire, using a random forest model. Recovery patterns were derived for all wildfires that occurred between 1986 and 2017 across seven forest types and 21 level III ecoregions of the western US. We found differences in the characteristic trajectories of post-fire vegetation recovery across forest types and eco-climatic settings. In some forest types, LAI had recovered to only 60 %–70 % of the pre-fire levels by 25 years after the fire, while it recovered to 120 %–150 % of the pre-fire levels in other forest types, with higher absolute post-fire changes observed in forest types and ecoregions that had a higher initial pre-fire LAI. Our random forest results showed very little influence of fire severity on the recovery of both summer LAI and albedo at both post-fire time horizons. Post-fire vegetation recovery was most strongly controlled by elevation, with faster rates of recovery at lower elevations. Similarly, annual precipitation and average summer temperature had significant impacts on the post-fire recovery of vegetation. Full recovery was seldom observed when annual precipitation was less than 500 mm and average summer temperature was above the optimal range, i.e., 15–20 °C. Climate influences, particularly annual precipitation, were a major driver of post-fire summer albedo change through its impact on ecological succession. This study provides quantitative measures of primary controls that could be used to improve the modeling of ecosystem dynamics post-fire.
... Forest ecosystems, as natural formations, are vulnerable to a range of natural and anthropogenic threats, which have significant impacts on ecosystem health and are often directly related to their degradation [1][2][3][4]. Wildfires are one of the threats that bring devastating results at environmental, economic and social levels [5,6]. Although it is a natural phenomenon that occurs extensively in all Mediterranean forest ecosystems, the frequency and magnitude of its occurrence in recent decades highlight the magnitude of the problem. ...
... Shrub and rocky areas should be avoided for afforestation. Moreover, black pine, as a cold-hardy conifer, should be given priority in restoration work over rough pine [1,2]. The next figure presents the initial vegetation map (Figure 5a) and the reclassified one (Figure 5b), which is one of the parameters of the methodology used. ...
Wildfires are a pervasive natural phenomenon in Mediterranean forest ecosystems, causing significant ecological imbalances that demand immediate restoration efforts. The intricacy of reinstating the ecological balance necessitates a proactive approach to identifying and assessing suitable restoration sites. The assessment and investigation of the most suitable restoration sites is of particular importance both for the relevant authorities and for planning and decision making by the state. This study proposes the development of a user-friendly model for evaluating and identifying the most suitable restoration sites immediately after a fire, using geoinformation technologies. For the purposes of demonstrating the method's applicability, the 2016 fire of "Prinos", Thasos, Greece, an area that has been repeatedly affected by forest fires, was chosen as a case study. The methodology evaluation was carried out by applying the weighted multicriteria decision analysis method (MC-DAM) and was based on a number of variables. The analysis, processing and extraction of the results were performed using primarily remote sensing datasets in a geographical information system (GIS) environment. The methodology proposed herein includes the classification of the individual criteria and their synthesis based on different weighting factors. In the final results, the restoration suitability maps are presented in five suitability zones based on two different scenarios. Based on this study, the integration of geospatial and remote sensing data offers a valuable and cost-effective means for promptly assessing post-fire landscapes, with the aim of identifying suitable restoration sites.
... Drier climates expected because of climate change, will affect Mediterranean populations of P. sylvestris (Martínez-Vilalta and Piñol 2002), such as those in central Spain. In addition, south-facing areas such as the one burnt in Jurisdicción, are less favourable for post-fire regeneration (Martín-Alcón and Coll 2016;Martínez-García et al. 2018), and influence fire severity (Oliveras et al. 2009). ...
... Non-serotinous pine forests in the Mediterranean are suffering from increased fire frequency, leading to vegetation shifts towards re-sprouters or fire-adapted communities, decreasing pine-dominated areas (Martín-Alcón and Coll 2016;Sánchez-Pinillos et al. 2018). Even in the absence of wildfires, species such as P. nigra show a decline in regeneration in the Mediterranean region because of drought (Fyllas et al. 2008). ...
Forest fires are frequent under a Mediterranean climate and have shaped the landscape of the region but are currently altered by human action and climate change. Fires have historically conditioned the presence of pine forests, depending on severity and forest regeneration. Regeneration of Mediterranean pine forests is not always successful, and a transition to shrublands or stands of resprouting species can occur, even after reforestation. This study analyses vegetation changes in two Mediterranean pine forests after severe fires and both reforested. The pines had difficulty to regenerate, even despite post-fire reforestation. The problem is the difficulty of young seedlings to survive, possibly due to increased summer drought. Problems are greater in pine species at the limit of their ecological tolerance: Pinus pinea had a much better recovery success while P. sylvestris and P. nigra virtually disappeared. Pinus pinaster had intermediate results but recovery was generally poor. A transition has taken place in many burnt areas to scrubland or to thickets of the resprouting Quercus rotundifolia, although it is not possible to know whether they will evolve into forests or remain in a sub climatic state. Resprouting species may increase fire severity but facilitates post-fire colonisation. Post-fire recovery difficulties are closely linked to issues of natural regeneration. Fire could initiate the disappearance of pine forests, but even in the absence of fire they may disappear in the long-term due to the lack of regeneration. Action is needed to increase the resilience of these forests, ensuring natural regeneration, and incorporating resprouting species in the understorey.
... In Africa, terrain slope has been reported to have a negative impact on the survival rate of Afzelia Africana [4]. Furthermore, studies have also shown that Mediterranean pine species have a high survival rate on north-facing compared to south-facing slopes because of lower radiation, which enhances cooler and mesic conditions [10,12]. A prolonged winter period often increases seedling mortality and reduces tree growth [13,14], which makes forest regeneration difficult, especially in regions close to the 'treeline', such as the north-western part of Sweden. ...
... This increases mortality and reduces growth [14]. Other studies [10,12,36] have reported greater growth and species diversity on north-facing slopes than south-facing slopes. This is expected in areas where moisture is a limiting factor because the increase in solar radiation increases evapotranspiration, which may induce drought and stress, and reduce tree growth [37][38][39][40]. ...
Tree development is affected by different factors including topographic features. The effect could be even more complex in harsh environments such as in the northwest of Sweden. In this study, we analyzed the effect of aspect-slope on the development up to the age of 34 years of five species: black spruce, lodgepole pine, Norway spruce, Siberian larch and Scots pine. The species were planted in a field experiment on the southwest slope, mountaintop, and northeast slope in a randomized complete block design in the northwest of Sweden (latitude 67°) with 2 m × 2 m spacing. No re-measurement data were available and, as such, retrospective diameters and heights were derived from sample discs and measurement of length to every branch whorl, respectively. Variations in tree survival rate, height and diameter were analyzed using a linear mixed-effect model. The results showed that there were significant (p < 0.05) differences between species in survival rate, diameter and height growth; in some cases, differences were found between contrasting aspect-slope. Black spruce and Siberian larch had the best survival rate under this harsh boreal climate. However, Siberian larch had the best growth and developed well on the mountaintop and northeast slope. Lodgepole pine developed well on the southwest slope. Scots pine also grew well on the southwest slope and mountaintop. Norway spruce had the slowest growth. Based on this study, Siberian larch and lodgepole pine can serve as alternatives to the two traditional conifer species, Norway spruce and Scots pine, used in Sweden. Siberian larch is particularly suitable because it is able to withstand the harshness of the boreal environment.
... Although the dynamic of post-fire vegetation recovery has been studied through different forest ecosystems, few studies have investigated the recovery driving factors in Mediterranean ecosystems [16,30,37,48] and fewer have focused on characterizing successional recovery stages [49,50], which are key to understanding forest changes for sustainable forest management. This study assesses the post-fire recovery dynamics at different stages in fire-prone Mediterranean pine forests. ...
... Bright et al. (2019) [28] also found that areas burned at higher severities recovered at faster rates, possibly because they are fire-adapted forest in which fire creates favorable conditions for vegetation germination and regeneration. Nevertheless, some studies in Mediterranean pine forest reported that conversion from forest to shrubland occurred in the most xeric sites (south-facing areas) [48] or in those areas with a high severity [12]. In this sense, Baudena et al. (2019) [90] predicted that future potential increases in aridity may drive these fire-prone ecosystems past a tipping point, after which closed forest structure would be replaced by open shrublands. ...
Wildfires constitute the most important natural disturbance of Mediterranean forests, driving vegetation dynamics. Although Mediterranean species have developed ecological post-fire recovery strategies, the impacts of climate change and changes in fire regimes may endanger their resilience capacity. This study aims at assessing post-fire recovery dynamics at different stages in two large fires that occurred in Mediterranean pine forests (Spain) using temporal segmentation of the Landsat time series (1994–2018). Landsat-based detection of Trends in Disturbance and Recovery (LandTrendr) was used to derive trajectory metrics from Tasseled Cap Wetness (TCW), sensitive to canopy moisture and structure, and Tasseled Cap Angle (TCA), related to vegetation cover gradients. Different groups of post-fire trajectories were identified through K-means clustering of the Recovery Ratios (RR) from fitted trajectories: continuous recovery, continuous recovery with slope changes, continuous recovery stabilized and non-continuous recovery. The influence of pre-fire conditions, fire severity, topographic variables and post-fire climate on recovery rates for each recovery category at successional stages was analyzed through Geographically Weighted Regression (GWR). The modeling results indicated that pine forest recovery rates were highly sensitive to post-fire climate in the mid and long-term and to fire severity in the short-term, but less influenced by topographic conditions (adjusted R-squared ranged from 0.58 to 0.88 and from 0.54 to 0.93 for TCA and TCW, respectively). Recovery estimation was assessed through orthophotos, showing a high accuracy (Dice Coefficient ranged from 0.81 to 0.97 and from 0.74 to 0.96 for TCA and TCW, respectively). This study provides new insights into the post-fire recovery dynamics at successional stages and driving factors. The proposed method could be an approach to model the recovery for the Mediterranean areas and help managers in determining which areas may not be able to recover naturally.
... The dynamics of vegetation recovery and its drivers have been studied in various ecological contexts [28,35,56]. In fact, post-fire monitoring of vegetation recovery and cover changes is essential for land management and damage prevention [57], particularly in mitigating habitat loss and biodiversity decline, which are two of the many risks associated with altered fire regimes and vegetation dynamics [58,59]. ...
Wildfires in the Mediterranean basin, particularly in Portugal, pose significant ecological challenges by altering landscapes and ecosystems. This study examines vegetation recovery in Serra do Açor seven years after the 2017 wildfires, using remote sensing and field data to analyze post-fire dynamics. The primary goal was to assess whether fire severity, measured via the dNBR index from Sentinel-2 imagery, impacts vegetation recovery or if site-specific factors and pre-fire floristic composition are more influential. Randomly assigned plots based on previous land use and fire severity were analyzed for floristic attributes. To quantify and classify cover changes, a supervised classification methodology based on the random forest algorithm was applied to Sentinel-2 data. The results showed no clear link between fire severity and recovery; instead, local factors like soil and topography, along with dominant pre-fire species, influenced recovery. Acacia and eucalyptus communities grew faster and increased the occupied area but exhibited lower diversity than native vegetation communities. Supervised classifications achieved high accuracy (Kappa > 0.90), showing increased shrubland areas and expansion of eucalyptus and acacia. The study highlights the methodology’s effectiveness and potential for broader applications in future research.
... This information is essential for addressing long-standing questions and theories in fire ecology, such as the "pyrodiversitybiodiversity" hypothesis [77]. Moreover, understanding post-fire recovery and its driving factors for species, communities, and ecosystems is a pivotal contribution of this stage to the grander wildfire research landscape [50,[78][79][80][81]. Research in the "after-fire" stage plays a critical role in guiding communities, stakeholders, and managers and acknowledging the challenges and opportunities of adequately managing post-fire landscapes and rebuilding communities. ...
As wildfires become more frequent and severe in the face of global environmental change, it becomes crucial not only to assess, prevent, and suppress them but also to manage the aftermath effectively. Given the temporal interconnections between these issues, we explored the concept of the “wildfire science loop”—a framework categorizing wildfire research into three stages: “before”, “during”, and “after” wildfires. Based on this partition, we performed a systematic review by linking particular topics and keywords to each stage, aiming to describe each one and quantify the volume of published research. The results from our review identified a substantial imbalance in the wildfire research landscape, with the post-fire stage being markedly underrepresented. Research focusing on the “after” stage is 1.5 times (or 46%) less prevalent than that on the “before” stage and 1.8 (or 77%) less than that on the “during” stage. This discrepancy is likely driven by a historical emphasis on prevention and suppression due to immediate societal needs. Aiming to address and overcome this imbalance, we present our perspectives regarding a strategic agenda to enhance our understanding of post-fire processes and outcomes, emphasizing the socioecological impacts of wildfires and the management of post-fire recovery in a multi-level and transdisciplinary approach. These proposals advocate integrating knowledge-driven research on burn severity and ecosystem mitigation/recovery with practical, application-driven management strategies and strategic policy development. This framework also supports a comprehensive agenda that spans short-term emergency responses to long-term adaptive management, ensuring that post-fire landscapes are better understood, managed, and restored. We emphasize the critical importance of the “after-fire” stage in breaking negative planning cycles, enhancing management practices, and implementing nature-based solutions with a vision of “building back better”. Strengthening a comprehensive and balanced research agenda focused on the “after-fire” stage will also enhance our ability to close the loop of socioecological processes involved in adaptive wildfire management and improve the alignment with international agendas such as the UN’s Decade on Ecosystem Restoration and the EU’s Nature Restoration Law. By addressing this research imbalance, we can significantly improve our ability to restore ecosystems, enhance post-fire resilience, and develop adaptive wildfire management strategies that are better suited to the challenges of a rapidly changing world.
... Few remote sensing studies in Mediterranean and other boreal forests revealed that tree density was an important predictor for post-fire vegetation patterns (Chu et al., 2017;João et al., 2018). Although the dynamics of vegetation recovery and its drivers have been studied under different ecological contexts (Fernández-Manso et al., 2016;Martín-Alcón and Coll, 2016;Viana-Soto et al., 2020), few study have focused on these dynamics across different vegetation stands of the Mediterranean. Such an approach would be important for gaining a deep understanding of forest dynamics, facilitating the creation and implementation of robust management-linked solutions. ...
Wildfires represent one of the primary disturbance agents in the Mediterranean, significantly affecting theecological integrity of forests. Therefore, understanding the spatial patterns of post-fire vegetation recovery iscrucial to improving forest restoration planning and assessing the regeneration capacity of different forest standsthat have been impacted by wildfires. In this study, we analysed post-fire vegetation recovery rates within thecontext of fire severity, pre-fire vegetation, and post-fire climate conditions, for different Mediterranean forestclasses, namely, Mediterranean pine, holm, deciduous oak forests, sclerophyllous vegetation, and thermophilousshrublands. Basilicata, in Italy, was chosen as a study area, as it represents a wide range of forests.The Relative Recovery Indicator (RRI) was derived from Normalized Burn Ratio (NBR) patterns extracted from30-meter Landsat time series for different wildfires that occurred during the 2004–2016 within Google EarthEngine (GEE) environment. A Linear Mixed Model (LMM) was used to test the effect of the different variables onthe RRI. Results showed a general decrease in recovery rate within five-years post-fire for each forest cover class,which is mainly related to pre- and post-fire conditions. Pre-fire vegetation conditions significantly influencedpost-fire vegetation recovery, especially in sclerophyllous and deciduous oak forests. Post-fire climate conditions(e.g., temperature) were also important predictors of vegetation recovery explaining the variation in post-fire RRIpatterns. The proposed method could provide new insights into the restoration and management of forest eco-systems in the Mediterranean
... Más allá de la riqueza de especies, lo que resulta relevante en términos de adaptación al cambio climático es aumentar la diversidad de rasgos funcionales del rodal (Sánchez-Pinillos et al., 2016;Messier et al., 2019). Por ejemplo, promover la progresiva diversificación de pinares monoespecíficos con especies de quercíneas puede resultar clave para el rápido recubrimiento del suelo por la vegetación tras un incendio, dada la capacidad de estas últimas de rebrotar (Martín-Alcón et al., 2016b). ...
El gestor forestal se enfrenta al desafío de tener que adaptar sus prácticas a un contexto de creciente incertidumbre ambiental, motivado por el cambio climático y las alteraciones en los regímenes de perturbaciones. El artículo repasa brevemente el concepto de gestión forestal adaptativa y las fases que componen este tipo de procesos. A continuación, identifica algunas líneas estratégicas de actuación a las que puede acogerse el gestor forestal para promover la progresiva adaptación de las masas al cambio climático y reforzar su resiliencia. Finalmente, remarca la importancia de monitorear adecuadamente la respuesta de las masas a los tratamientos ejecutados para poder evaluar, en base a ello, su pertinencia para la consecución de los objetivos perseguidos. Además, aboga por continuar estableciendo nuevas parcelas de seguimiento y ensayos y exprimir el potencial de las nuevas tecnologías y de los avances existentes en materia de análisis de datos y modelización para el ajuste y mejora de la práctica selvícola y de la planificación forestal.
... Fire regime alterations and direct climate change effects are producing noticeable consequences and endangering tree regeneration in dry conifer forests of the Alps, where Pinus sylvestris L. is often the dominant species [11][12][13][14]. Similarly to other non-serotinous pine species lacking direct post-fire regeneration mechanisms, this obligate seeder has been defined as a fire tolerator, able to survive lower intensity surface fires but highly sensitive to crown fires [15,16]. Despite being a pioneer species, P. sylvestris younger seedlings are highly dependent on a sufficient water supply and require a stable soil moisture regime [17]. ...
After large and severe wildfires, the establishment of tree regeneration, particularly for species without specific fire-adaptive traits, can be challenging. Within harsh environments, the presence of favorable microsites, as those provided by deadwood, enhancing microclimatic conditions, is crucial to the re-establishment of forest cover and thus to foster recovery dynamics. Active restoration strategies can have an impact on these dynamics, altering or hindering them. The main hypothesis of this study is that manipulating deadwood in terms of quantity and spatial arrangement can result in differences in natural regeneration density and composition. Post-disturbance regeneration dynamics and the role played by deadwood over time in the creation of safe sites for seedling establishment were investigated in an area affected by a high-severity wildfire that underwent different post-fire restoration treatments along a gradient of increasing deadwood manipulation, spanning from salvage logging to non-intervention. Two inventories were performed 5 and 11 years after the fire. Ground cover proportion was significantly different among treatments, with lower values of lying deadwood in salvaged sites. A higher probability of regeneration establishment close to deadwood was found in both surveys, confirming the facilitating role of deadwood on post-fire forest regeneration. Microsite dynamics resulting from deadwood facilitation were highlighted, with establishment probability and anisotropic relationships between deadwood elements and seedlings changing over time, as recovery processes slowly improved environmental conditions. In dry mountain areas affected by stand-replacing wildfires, by removing deadwood, salvage logging reduces the number of safe sites for regeneration, further impairing the ecosystem recovery. Passive management should be the ecologically preferred management strategy in these conditions, although intermediate interventions (e.g., felling without delimbing, leaving deadwood on the ground) could be effective alternatives, accelerating snag fall dynamics and immediately increasing favorable microsite availability.
... However, challenges in obtaining permits and restrictions in certain areas can hinder these strategies being implemented. Nevertheless, PBs play a crucial role in mitigating disturbances such as grazing and ensure the resilience of Pinus nigra, known for its wind and drought resistance, erosion control capabilities, and extensive use in reforestation programs [27,28]. ...
Worsening climate change and increasing temperatures generate more sever and extended wildfires, raising concerns about ecosystem services. Prescribed burns (PB) are used to reduce forest fuel loads. Improving knowledge regarding the vegetation response after PB is essential for generating common points for monitoring ecological burning effects and generating a protocol or practice guide. We compared the PB seasonality of low-intensity (spring, summer, and autumn) and unburned areas in a total of 12 plots in Pinus nigra Arnold ssp. salzmannii Mediterranean forest. Our vegetation analysis was short term (one year after each PB). We analyzed vegetation coverage, α-diversity (Pielou, Simpson, and Shannon’s index), life forms, and fire-adapted traits using the Canfield transect method, followed by statistical analyses such as non-metric multidimensional scaling (NMDS) and two-way ANOVA. α-diversity was significantly decreased (>55% of dissimilarity) in the burned plots during each season, with the lowest values after summer PB (69% of dissimilarity) when comparing the burned and unburned plots. There was a significant increase in hemicryptophytes (15−20%) and geophyte coverage (from 6% to 14%, or from 4% to 8% in certain cases) in the burned plots after PB seasonality; however, the phanerophytes were reduced (from 13% to 5%). Resprouters were more dominant after PB (an increase of 15–20%), which indicates that resprouters have a faster recovery and generate a fuel load quickly for highly flammable species such as Bromus after low-intensity burning. This suggests that low-intensity prescribed burning may not be the best methodology for these resprouting species. This study helps to understand how burning in the early season can affect inflammable vegetation and the change in fuel that is available in semi-arid landscapes. This is key to achieving the basis for the development of a standardized system that allows for the efficient management of forest services in order to reduce wildfire risks. One objective of this line of research is to observe the effects of recurrent burning in different seasons on vegetation, as well as plant−soil interaction using the microbial and enzyme soil activity.
Keywords: prescribed burning; vegetation parameters; biodiversity; preventive tools; ecological effects; Mediterranean forest; forest management; vegetation response
... Early post-fire recovery and regeneration dynamics in Scots pine stands of the Alpine Region is a poorly explored issue that needs to be monitored. This species lacks a resilience strategy (e.g., serotiny) to promptly recover after a fire (Tapias et al. 2004), and is particularly sensitive to crown fires with no direct post-fire regeneration mechanisms (Pausas et al. 2008;Vilà-Cabrera et al. 2011;Martín-Alcón and Coll 2016). Nevertheless, the fire regime in the Alpine Region will likely be altered because of global change, and the limited post-fire regeneration capacity of Scots pine could lead to a transition in species composition (Rodrigo et al. 2004;Vilà-Cabrera et al. 2011). ...
Background
The Mediterranean basin is currently facing major changes in fire regimes as a result of climate and land-use changes. These alterations could affect the ability of forests to recover after a fire, hence triggering degradation processes and modifying the provision of fundamental ecosystem services. Examining patterns and drivers of post-fire forest recovery, particularly for obligate seeders without specific fire-adaptive traits, thus becomes a priority for researchers and land managers. We studied the post-fire dynamics of Scots pine ( Pinus sylvestris L.) stands affected by a mixed-severity fire in North-Western Italy, aiming to understand the impact of fire on soil properties and assess drivers, spatial distribution, and characteristics of short-term post-fire recovery.
Results
We observed that fire did not significantly affect soil organic carbon (OC) content, while we detected significantly lower nitrogen (N) content in severely burnt sites. Regeneration density was particularly abundant in medium-severity areas, while it drastically decreased in high-severity patches. The most abundant tree species in the regeneration layer was Scots pine, followed by goat willow ( Salix caprea L.), European aspen ( Populus tremula L.), and, to a lesser extent, European larch ( Larix decidua Mill.). Slope, fire severity, and distance from seed trees emerged as the most important drivers of post-fire forest regeneration patterns.
Conclusions
Our results highlight the importance of preserving seed trees from salvage logging, even if they are damaged and have a low survival probability. Active post-fire management, such as tree planting, should be limited to large and severely burnt patches, where natural forest regeneration struggles to settle, increasing the risk of ecosystem degradation. These findings could be useful for informing land managers, helping them to enhance potential mitigation strategies in similar ecosystems and plan appropriate restoration approaches.
... However, we find this assumption rather realistic, given that the management scenarios were designed with local experts based on the achievement of specific objectives through pine management, and thus assumed the dominance of pine throughout the simulated period. Obviously, further analyses considering transitions into Quercus species (e.g., Quercus ilex; Quercus faginea) would lead to a more complete picture of the forecasted dynamics (Martín-Alcón and Coll, 2016), but were beyond the aim of this study. Furthermore, fire behavior simulation involves a large number of parameters influencing the outcomes, being particularly prone to errors when fuel treatments are involved such as uncertainties in projecting fuel accumulation and the role of decomposition or the effects of canopy openness in wind speed (Hanan et al., 2022;Varner and Keyes, 2009). ...
Mediterranean forests and fire regimes are closely intertwined. Global change is likely to alter both forest dynamics and wildfire activity, ultimately threatening the provision of ecosystem services and posing greater risks to society. In this paper we evaluate future wildfire behavior by coupling climate projections with simulation models of forest dynamics and wildfire hazard. To do so, we explore different forest management scenarios reflecting different narratives related to EU forestry (promotion of carbon stocks, reduction of water vulnerability, biomass production and business-as-usual) under the RCP 4.5 and RCP 8.5 climate pathways in the period 2020–2100. We used as a study model pure submediterranean Pinus nigra forests of central Catalonia (NE Spain). Forest dynamics were simulated from the 3rd National Forest Inventory (143 stands) using SORTIE-nd software based on climate projections under RCPs 4.5 and 8.5. The climate products were also used to estimate fuel moisture conditions (both live and dead) and wind speed. Fuel parameters and fire behavior were then simulated, selecting crown fire initiation potential and rate of spread as key indicators. The results revealed consistent trade-offs between forest dynamics, climate and wildfire. Despite the clear influence exerted by climate, forest management modulates fire behavior, resulting in different trends depending on the climatic pathway. In general, the maintenance of current practices would result in the highest rates of crown fire activity, while management for water vulnerability reduction is postulated as the best alternative to surmount the increasingly hazardous conditions envisaged in RCP 8.5.
... Although high-severity fires significantly reduce fuel loads and continuity, there is a tendency to repeated high-severity fires due to the remaining fuels (e.g. dead trees, moss and duff), thereby preventing vegetation recovery (Shive et al. 2018;Lydersen et al. 2019). Extreme fire conditions, such as drought, can lead to increasing reburn likelihood in many burned areas with lower fuel loads (Littell et al. 2016;Keyser and Westerling 2017). ...
Background
Repeated fires may slow the recovery process in burned areas, thus affecting ecological succession.
Aims
This paper explores the changes in likelihood of reburn and fire behaviours in various phases of vegetation recovery.
Methods
We used field survey data and the Enhanced Vegetation Index (EVI) to assess vegetation recovery in boreal forests after fires at both landscape and field scales. The Burn-P3 model was used to simulate burn probability and fire behaviours and then evaluate the overall fire likelihood and potential behaviours in different recovery phases.
Key results
Vegetation began to recover in most burned areas within the first year after fire and reached prefire levels after 10–15 years of recovery. Vegetation in areas with steep slopes (>25°) and thin soil had not recovered after 20 years, accounting for 0.3% of the total burned area. The average burn probability and fire behaviour indices of the study area decreased significantly after fire owing to lower fuel levels.
Conclusions
Burned areas with steep slopes and thin soil showed slower recovery rates after fire. The recovered vegetation in most burned areas still had low burn likelihood and fire behaviours 20 years post burn.
Implications
Artificial regeneration and fire prevention should be carried out at highly vulnerable sites for rehabilitating forest ecosystems.
... Cluster analysis identified four vegetation types indicative of successional trajectories away from forested conditions, referred to here as oak scrub, mixed shrub, bunchgrass, and ruderal grass communities. Severe fire-driven conversion from conifer forest to resprouting shrublands is an emerging phenomenon across a range of temperate forest systems globally (e.g., Airey Lauvaux et al., 2016;Barton and Poulos, 2018;Martín-Alcón and Coll, 2016). These transitions may also be associated with positive fire-vegetation feedbacks that increase the likelihood and/or severity of subsequent fire (Landesmann et al. 2020;Tepley et al., 2017), and may thus represent persistent alternate stable states (Falk, 2017) or "landscape traps" (Lindenmayer et al., 2011). ...
Southwestern ponderosa pine forests are vulnerable to fire‐driven conversion in a warming and drying climate, yet little is known about what kinds of ecological communities may replace them. To characterize postfire vegetation trajectories and their environmental determinants, plant assemblages (361 sample plots including 229 vascular plant species, surveyed in 2017) were sampled within eight burns that occurred between 2000 and 2003. I used nonmetric multidimensional scaling, k‐means clustering, principal component analysis, and random forest models to assess relationships between vegetation pattern, topographic and landscape factors, and gridded climate data. I describe seven postfire community types, including regenerating forests of ponderosa pine, aspen, and mixed conifers, shrub‐dominated communities of Gambel oak and mixed species, and herb‐dominated communities of native bunchgrasses and mixtures of ruderal, native, and nonnative species. Forest recovery was generally associated with cooler, mesic sites in proximity to forested refugia; shifts toward scrub and grassland types were most common in warmer, dryer locations distant from forested refugia. Under future climate scenarios, models project decreases in postfire forest recovery and increases in nonforest vegetation. However, forest to nonforest conversion was partially offset under a scenario of reduced burn severity and increased retention of forested refugia, highlighting important management opportunities. Burning trends in the southwestern United States suggest that postfire vegetation will occupy a growing landscape fraction, compelling renewed management focus on these areas and paradigm shifts that accommodate ecological change. I illustrate how management decisions around resisting, accepting, or directing change could be informed by an understanding of processes and patterns of postfire community variation and likely future trajectories.
... Rainfall was the only significant factor for shrub community growth, and both daytime and rainfall acted on the regeneration of forest communities. Furthermore, terrain and other factors also have an important impact on vegetation regeneration [113,114]. By randomly sampling on a spatial scale, we found that the best slope for vegetation regeneration was 15-35 • . ...
Studying the early changes in post-fire vegetation communities may improve the overall resilience of forests. The necessity for doing so was demonstrated by the Bobcat Fire, which seriously threatened the central San Gabriel Mountains and the Angeles National Forest in California. This study aimed to monitor and quantify the effects of climatological and topographic conditions along with burn severity on early (within 1 year) post-fire forests and shrubs community regeneration. In this study, we used Sentinel-2(MSI) intensive time-series imagery (July 2020–October 2021) to make a confusion matrix combined with 389 vegetation sample points on Google Earth Pro. The overall accuracy (OA) and the Kappa coefficient, calculated from the confusion matrix, were used as evaluation parameters to validate the classification results. With multiple linear regression models and Environmental Systems Research Institute (ESRI) historical images, we analyzed the effects of climate and slope aspects on the regeneration of post-fire forest and shrub communities. We also quantitatively analyzed the regeneration rates based on five burn severity types. The results show that the normalized burning rate (NBR) was the most accurate vegetation classification indicator in this study (OA: 92.3–99.5%, Kappa: 0.88–0.98). The vegetation classification accuracy based on SVM is about 6.6% higher than K-Means. The overall accuracy of the burn area is 94.87%. Post-fire climate factors had a significant impact on the regeneration of the two vegetation communities (R²: 0.42–0.88); the optimal regeneration slope was 15–35°; and the fire severity changed the original competition relationship and regeneration rate. The results provide four main insights into the regeneration of post-fire vegetation communities: (1) climate factors in the first regenerating season have important impacts on the regeneration of forest and shrub communities; (2) daytime duration and rainfall are the most significant factors for forests and shrubs regeneration; (3) tolerable low burn severity promotes forests regeneration; and (4) forests have a certain ability to resist fires, while shrubs can better tolerate high-intensity fire ecology. This study could support the implementation of strategies for regionalized forest management and the targeted enhancement of post-fire vegetation community resilience.
... As a result, the fires rapidly evolved from fuel-limited short-events to weather-driven catastrophic events [33]. In central Catalonia (northeastern Spain), these new forest structures fostered stand-replacing high severity wildfires associated with increased mortality rates on the non-serotinous sub-Mediterranean conifers forests [34,35]. Similarly, extreme fires that burned broadleaved forests triggered significant changes in stand structures (i.e., conversion to coppice forest or scrublands), hampering woodlands' management and economic viability of many products, such as cork oak production and extraction [36]. ...
Despite the need for preserving the carbon pools in fire-prone southern European landscapes, emission reductions from wildfire risk mitigation are still poorly understood. In this study, we estimated expected carbon emissions and carbon credits from fuel management projects ongoing in Catalonia (Spain). The planning areas encompass about 1000 km 2 and represent diverse fire regimes and Mediterranean forest ecosystems. We first modeled the burn probability assuming extreme weather conditions and historical fire ignition patterns. Stand-level wildfire exposure was then coupled with fuel consumption estimates to assess expected carbon emissions. Finally, we estimated treatment cost-efficiency and carbon credits for each fuel management plan. Landscape-scale average emissions ranged between 0.003 and 0.070 T CO2 year −1 ha −1. Fuel treatments in high emission hotspots attained reductions beyond 0.06 T CO2 year −1 per treated ha. Thus, implementing carbon credits could potentially finance up to 14% of the treatment implementation costs in high emission areas. We discuss how stand conditions, fire regimes, and treatment costs determine the treatment cost-efficiency and long-term carbon-sink capacity. Our work may serve as a preliminary step for developing a carbon-credit market and subsidizing wildfire risk management programs in low-revenue Mediterranean forest systems prone to extreme wildfires.
... Natural rates of postfire regeneration across conifer forests are highly inconsistent over space and time (Shatford et al. 2007, Frazier et al. 2018). Variability in rates of recovery and postfire trajectories have been attributed to prefire forest condition (Kasischke and French 1997, Martín-Alcón and Coll 2016, Zhao et al. 2016, Chu et al. 2017, site topography including slope, aspect, and elevation (Chambers et al. 2016, Haffey et al. 2018, and postfire climate including temperature and moisture Manuscript received 1 May 2020; revised 1 July 2020; accepted 16 August 2020; final version received 13 October conditions (Meng et al. 2015, Kemp et al. 2019. Several parameters tend to show a consistent directionality across such studies. ...
Postfire shifts in vegetation composition will have broad ecological impacts. However, information characterizing postfire recovery patterns and their drivers are lacking over large spatial extents. In this analysis, we used Landsat imagery collected when snow cover (SCS) was present, in combination with growing season (GS) imagery, to distinguish evergreen vegetation from deciduous vegetation. We sought to (1) characterize patterns in the rate of postfire, dual‐season Normalized Difference Vegetation Index (NDVI) across the region, (2) relate remotely sensed patterns to field‐measured patterns of re‐vegetation, and (3) identify seasonally specific drivers of postfire rates of NDVI recovery. Rates of postfire NDVI recovery were calculated for both the GS and SCS for more than 12,500 burned points across the western United States. Points were partitioned into faster and slower rates of NDVI recovery using thresholds derived from field plot data (n = 230) and their associated rates of NDVI recovery. We found plots with conifer saplings had significantly higher SCS NDVI recovery rates relative to plots without conifer saplings, while plots with ≥50% grass/forbs/shrubs cover had significantly higher GS NDVI recovery rates relative to plots with <50%. GS rates of NDVI recovery were best predicted by burn severity and anomalies in postfire maximum temperature. SCS NDVI recovery rates were best explained by aridity and growing degree days. This study is the most extensive effort, to date, to track postfire forest recovery across the western United States. Isolating patterns and drivers of evergreen recovery from deciduous recovery will enable improved characterization of forest ecological condition across large spatial scales.
... They also have a clear ecological meaning, a key need highlighted in the literature (Keeley, 2009). In this sense, UB and PCU categories can be considered fire refugia (Blomdahl et al., 2019) and a metric of the landscape's resilience (Donato et al., 2009;Martín-Alcón and Coll, 2016). CS is also associated with both short-and long-term benefits to forest recovery, as it provides nutrients and "safe sites" (Christopoulou et al., 2014) for protecting seeds, along with mitigating erosion (Castro et al., 2011;Pausas et al., 2002). ...
https://authors.elsevier.com/a/1bYne7qzSr75H
... RF, for example, has been a popular ML method for understanding the important variables driving post-fire regeneration (João, João, Bruno, & João, 2018;Vijayakumar et al., 2016). Burn severity (a measure of above and below ground biomass loss due to fire) is an important metric for understanding the impacts of wildfire on vegetation and post-fire regeneration, soils, and potential successional shifts in forest composition, and as such, has been included in many ML studies in this section, including (Barrett, McGuire, Hoy, & Kasischke, 2011;Cai, Yang, Liu, Hu, & Weisberg, 2013;Cardil, Mola-Yudego, Blázquez-Casado, & González-Olabarria, 2019;Chapin, Hollingsworth, & Hewitt, 2014;Divya & Vijayalakshmi, 2016;Fairman, Bennett, Tupper, & Nitschke, 2017;Han, Shen, Ying, Li, & Chen, 2015;Johnstone, Hollingsworth, Chapin, & Mack, 2010;Martín-Alcón & Coll, 2016;Sherrill & Romme, 2012; J. R. Thompson & Spies, 2010). For instance, Cardil et al. (2019) used BRT to demonstrate that remotely-sensed data (i.e., Relative Differenced Normalized Burn Ratio index; RdNBR) can provide an acceptable assessment of fireinduced impacts (i.e., burn severity) on forest vegetation, while (Fairman et al., 2017) used RF to identify the variables most important in explaining plot-level mortality and regeneration of Eucalyptus pauciflora in Victoria, Australia, affected by high-severity wildfires and subsequent re-burns. ...
Artificial intelligence has been applied in wildfire science and management since the 1990s, with early applications including neural networks and expert systems. Since then, the field has rapidly progressed congruently with the wide adoption of machine learning (ML) methods in the environmental sciences. Here, we present a scoping review of ML applications in wildfire science and management. Our overall objective is to improve awareness of ML methods among wildfire researchers and managers, as well as illustrate the diverse and challenging range of problems in wildfire science available to ML data scientists. To that end, we first present an overview of popular ML approaches used in wildfire science to date and then review the use of ML in wildfire science as broadly categorized into six problem domains, including (i) fuels characterization, fire detection, and mapping; (ii) fire weather and climate change; (iii) fire occurrence, susceptibility, and risk; (iv) fire behavior prediction; (v) fire effects; and (vi) fire management. Furthermore, we discuss the advantages and limitations of various ML approaches relating to data size, computational requirements, generalizability, and interpretability, as well as identify opportunities for future advances in the science and management of wildfires within a data science context. In total, to the end of 2019, we identified 300 relevant publications in which the most frequently used ML methods across problem domains included random forests, MaxEnt, artificial neural networks, decision trees, support vector machines, and genetic algorithms. As such, there exists opportunities to apply more current ML methods — including deep learning and agent-based learning — in the wildfire sciences, especially in instances involving very large multivariate datasets. We must recognize, however, that despite the ability of ML models to learn on their own, expertise in wildfire science is necessary to ensure realistic modelling of fire processes across multiple scales, while the complexity of some ML methods such as deep learning requires a dedicated and sophisticated knowledge of their application. Finally, we stress that the wildfire research and management communities play an active role in providing relevant, high-quality, and freely available wildfire data for use by practitioners of ML methods.
... In addition, pine seedlings present a fast root growth and a remarkable soil penetration capacity [25], which enable them to withstand competition from the neighboring ground vegetation by rapidly reaching deeper soil horizons. However, in stands with a well-developed canopy cover, competition for light can limit growth of the seedlings and delay the progressive advance of the recruitment towards more advanced stages [44]. Among the sites in this study, unmanaged areas accounted for the best seedling emergence. ...
Skidding operations are thought to have negative impacts on soil emergence because they may increase soil compaction and reduce vegetation cover and the soil’s organic matter content. We investigated whether and to what extent tree harvesting and subsequent skidding initially altered seedling emergence in two Mediterranean forests of Pinus nigra Arn. ssp. salzmannii (Spanish black pine) in the Cuenca Mountains (Spain). Our main objective was to compare the Spanish black pine seedling emergence rate among skid trails, soil areas scarified by felled trees, and areas undisturbed next to harvest operations. In addition, we selected an unmanaged stand as reference, in order to look for evidence of seedling emergence under natural conditions. We measured Spanish black pine seed fall and seedling emergence immediately after harvest operations in two locations in the Cuenca Mountains (Palancares and Majadas forests), which are typical forests in Cuenca Mountains. The results showed that the Palancares site presented higher seed fall in comparison to the Majadas site. In addition, seed fall was higher in the unmanaged stand, as we recorded a higher tree density in this site in comparison to harvested stands (Palancares and Majadas). Furthermore, our results demonstrated differences in seedling emergence between lower elevation drier Palancares and higher elevation wetter Majadas and relative differences in seedling emergence among skid trail, scarified, and undisturbed harvested areas. Finally, the unmanaged stand presented the highest seedling emergence in comparison to scarified, compacted, and non-disturbed harvested areas. Overall, the results suggest a short-term impact of skidding on seedling emergence, which should be considered for future management guidelines of Spanish black pine in the Mediterranean climate.
... This observation points to the involvement of other factors. The influence of the main physiographic variables on the regeneration process has been largely documented, and numerous studies have emphasized the role of elevation, slope and topography as key factors influencing above-and below-ground conditions, and thereby regeneration success (e.g., Peterson and Pickett, 1990;van Mantgem et al., 2006;Martín-Alcón and Coll, 2016). The relationships linking regeneration and soil physical and chemical properties have also been explored (e.g., Kabrick et al., 2005;Hattori et al., 2013), although our understanding of them is still limited (Dickie et al., 2007). ...
This study assesses the effects of vegetation patterns and environmental factors on the abundance of natural tree and shrub regeneration in semi-arid forests of the Zagros Mountains, western Iran. We sampled 120 releves at different topographic positions in a protected area of the studied region. Floristic composition, slope, elevation and soil properties were recorded at each releve, and woody seedling density was measured. We have first discerned five floristic groups using two-way indicator species analysis (TWINSPAN) and detrended correspondence analysis (DCA) and then explored the relationships among the floristic group compositions, environmental factors and seedling densities. The indicator species of the 5 groups were Quercus brantii, Acer monspessulanum, Cerasus microcarpa, Rhamnus arvensis and Astragalus licyoides. Our results indicated that these groups were significantly affected by elevation and soil properties and the soil properties refer to: EC (electrical conductivity), N (nitrogen), K (potassium), OM (organic matter), and bulk density. Woody regeneration was composed of Q. brantii, A. monspessulanum, C. microcarpa, Amygdalus scoparia and Crataegus pontica seedlings. The highest density of seedlings was found for Q. brantii (97.14 (±48.00)/hm2) and the lowest for A. scoparia (2.28 (±1.50)/hm2). Quercus brantii was the dominant species and the seedling density was positively correlated with soil pH and P (phosphorus) values. A. scoparia regeneration was negatively correlated with elevation, and the seedling density peaked in C. microcarpa group. There was no significant variation in distribution of C. pontica seedlings among the groups, but the seedling density of this species was positively correlated with slope and potassium. Cerasus microcarpa seedlings were more abundant in the Q. brantii group than in other groups. This study showed that the regeneration of trees and shrub species was unequally distributed in different floristic groups for some species (A. scoparia and C. microcarpa) but not for other (Q. brantii and C. pontica) and was generally correlated with some environmental factors, particularly elevation, slope and soil nutrients (P and K). These results are a first step to implement future management and restoration strategies for promoting forest regeneration.
... RF, for example, has been a popular ML method for understanding the important variables driving post-fire regeneration (João, João, Bruno, & João, 2018;Vijayakumar et al., 2016). Burn severity (a measure of above and below ground biomass loss due to fire) is an important metric for understanding the impacts of wildfire on vegetation and post-fire regeneration, soils, and potential successional shifts in forest composition, and as such, has been included in many ML studies in this section, including (Barrett, McGuire, Hoy, & Kasischke, 2011;Cai, Yang, Liu, Hu, & Weisberg, 2013;Cardil, Mola-Yudego, Blázquez-Casado, & González-Olabarria, 2019;Chapin, Hollingsworth, & Hewitt, 2014;Divya & Vijayalakshmi, 2016;Fairman, Bennett, Tupper, & Nitschke, 2017;Han, Shen, Ying, Li, & Chen, 2015;Johnstone, Hollingsworth, Chapin, & Mack, 2010;Martín-Alcón & Coll, 2016;Sherrill & Romme, 2012; J. R. Thompson & Spies, 2010). For instance, Cardil et al. (2019) used BRT to demonstrate that remotely-sensed data (i.e., Relative Differenced Normalized Burn Ratio index; RdNBR) can provide an acceptable assessment of fireinduced impacts (i.e., burn severity) on forest vegetation, while (Fairman et al., 2017) used RF to identify the variables most important in explaining plot-level mortality and regeneration of Eucalyptus pauciflora in Victoria, Australia, affected by high-severity wildfires and subsequent re-burns. ...
Artificial intelligence has been applied in wildfire science and management since the 1990s, with early applications including neural networks and expert systems. Since then the field has rapidly progressed congruently with the wide adoption of machine learning (ML) in the environmental sciences. Here, we present a scoping review of ML in wildfire science and management. Our objective is to improve awareness of ML among wildfire scientists and managers, as well as illustrate the challenging range of problems in wildfire science available to data scientists. We first present an overview of popular ML approaches used in wildfire science to date, and then review their use in wildfire science within six problem domains: 1) fuels characterization, fire detection, and mapping; 2) fire weather and climate change; 3) fire occurrence, susceptibility, and risk; 4) fire behavior prediction; 5) fire effects; and 6) fire management. We also discuss the advantages and limitations of various ML approaches and identify opportunities for future advances in wildfire science and management within a data science context. We identified 298 relevant publications, where the most frequently used ML methods included random forests, MaxEnt, artificial neural networks, decision trees, support vector machines, and genetic algorithms. There exists opportunities to apply more current ML methods (e.g., deep learning and agent based learning) in wildfire science. However, despite the ability of ML models to learn on their own, expertise in wildfire science is necessary to ensure realistic modelling of fire processes across multiple scales, while the complexity of some ML methods requires sophisticated knowledge for their application. Finally, we stress that the wildfire research and management community plays an active role in providing relevant, high quality data for use by practitioners of ML methods.
... In old fields, assemblies of shrubs and pines without oaks prevail under the current fire regime Pausas & Lloret, 2007;L opez-Poma et al., 2014), with pine disappearing under repeated fires (Daskalakou & Thanos, 1996;Eugenio & Lloret, 2004). However, direct observations also show that fires can transform pine forests into oak forests if the latter are present in the understory (Retana et al., 2002;Torres et al., 2016;Vayreda et al., 2016;Mart ın-Alc on & Coll, 2016). The present model results also reinforced state-of-the-art restoration findings, showing that the planting of resprouting oaks in shrublands significantly redirects and accelerates the transition towards late-successional oak communities (Santana et al., 2018). ...
Recent observations suggest that repeated fires could drive Mediterranean forests to shrublands, hosting flammable vegetation that regrows quickly after fire. This feedback supposedly favours shrubland persistence and may be strengthened in the future by predicted increased aridity. An assessment was made of how fires and aridity in combination modulated the dynamics of Mediterranean ecosystems and whether the feedback could be strong enough to maintain shrubland as an alternative stable state to forest.
A model was developed for vegetation dynamics, including stochastic fires and different plant fire‐responses. Parameters were calibrated using observational data from a period up to 100 yr ago, from 77 sites with and without fires in Southeast Spain and Southern France.
The forest state was resilient to the separate impact of fires and increased aridity. However, water stress could convert forests into open shrublands by hampering post‐fire recovery, with a possible tipping point at intermediate aridity.
Projected increases in aridity may reduce the resilience of Mediterranean forests against fires and drive post‐fire ecosystem dynamics toward open shrubland. The main effect of increased aridity is the limitation of post‐fire recovery. Including plant fire‐responses is thus fundamental when modelling the fate of Mediterranean‐type vegetation under climate‐change scenarios.
... This pattern has been observed in some southwestern ponderosa pine forests Strom and Fulé, 2007) and in forests that are taxonomically related to ponderosa pine with similar adaptations to frequent fire (P. arizonica, P. durangensis, P. engelmannii and P. nigra) (McCune, 1988;Fulé and Covington, 1998;Martín-Alcón and Coll, 2016). However, it is unclear whether or not regenerating ponderosa pines in large, high-severity burn patches will exhibit random associations, attraction (implying facilitation or similar habitat preferences) or repulsion (implying a negative interaction like competition, or different habitat preferences) with sprouting tree species (Luo et al., 2012). ...
... However, the most diverse stages also showed higher response capacity to wildfires. Previous studies have reported a positive relationship between species diversity and resilience since a larger number of species are more likely to contribute with different response traits (Martín-Alcón and Coll, 2016;Sánchez-Pinillos et al., 2016). Just like pine-dominated forests presenting resilient shrubs in the understory, in case of a severe wildfire, a given community will not necessarily recover following the dynamical patterns identified. ...
Understanding ecosystem vulnerability is essential in risk management to anticipate disasters. While valuable efforts have been made to characterize vulnerability components (exposure, sensitivity, and response capacity) at particular ecosystem stages, there is still a lack of context-specific studies accounting for the temporal dimension of vulnerability. In this study, we developed a procedure to identify the main natural dynamics of monospecific and mixed forests and to assess the variations of sensitivity and response capacity to fire along successional dynamics. In the procedure, we generated forest chronosequences by summarizing the dynamics between consecutive surveys of permanent plots into a set of longer successional trajectories represented in a multidimensional space. Then, we calculated several variables of sensitivity and response capacity to fire of forest stages associated with each trajectory and we assessed their variation along succession. The procedure was applied to Mediterranean forests in Spain dominated by a pine species poorly adapted to severe crown fires. We found that forest vulnerability components varied differently among successional trajectories, which depended on the composition and structure of their initial stages and the environmental context in which they occurred. Autosuccessional dynamics of pine forests showed relatively low sensitivity to fire along trajectories. However, their response capacity was related to the changes in shrub cover. In contrast, diversifying dynamics showed an increasing sensitivity to fire, but also a higher response capacity the greater the functional diversity along succession. These results highlight the need for considering the temporal dimension of vulnerability in risk management and the importance of assessing sensitivity and response capacity as independent components of vulnerability that can be modified through management at critical forest stages.
... When no seed sources of another tree species are present, creating mixed forests in pure stands could also be achieved by underplanting (i.e., enrichment plantations) or direct seeding beneath the canopy of pure stands ( Paquette et al. 2006;Ammer et al. 2008;Martín-Alcón and Coll 2016) (Fig. 4.2b). When conducting such practices (see below in Sect. ...
Mixed forests have been proposed as a tool for more flexible wood production that simultaneously improves conditions for biodiversity and various social demands. Therefore, regeneration of mixed forests has become an important topic of practical concern throughout the world. Here, we briefly review important ecological processes in the early phases of stand development. In addition, we review the various regeneration techniques that can be used, i.e. natural and artificial regeneration of mixtures. Our paper highlights some important knowledge gaps for improved management of young mixed-species stands in Europe. For example, few studies have addressed the specific seed production conditions in mixed forests. Thus, even if some management recommendations can be given for mixed-species regeneration, predicting natural regeneration in mixed stands is problematic. Generally, it is more complicated to formulate rules for young mixed stand development than for monocultures. Much species-specific knowledge is still lacking regarding responses to interactions, although from a management perspective it seems easier to manage mixtures group-wise rather than stem-wise. Finally, we highlight high deer populations as perhaps the greatest challenge for mixed forest regeneration. More knowledge in the field and greater cooperation between researchers and different stakeholder groups is needed to solve this problem.
... When no seed sources of another tree species are present, creating mixed forests in pure stands could also be achieved by underplanting (i.e., enrichment plantations) or direct seeding beneath the canopy of pure stands ( Paquette et al. 2006;Ammer et al. 2008;Martín-Alcón and Coll 2016) (Fig. 4.2b). When conducting such practices (see below in Sect. ...
Mixed forests have been proposed as a tool for more flexible wood production that simultaneously improves conditions for biodiversity and various social demands. Therefore, regeneration of mixed forests has become an important topic of practical concern throughout the world. Here, we briefly review important ecological processes in the early phases of stand development. In addition, we review the various regeneration techniques that can be used, i.e., natural and artificial regeneration of mixtures. Our paper highlights some important knowledge gaps for improved management of young mixed-species stands in Europe. For example, few studies have addressed the specific seed production conditions in mixed forests. Thus, even if some management recommendations can be given for mixed-species regeneration, predicting natural regeneration in mixed stands is problematic. Generally, it is more complicated to formulate rules for young mixed stand development than for monocultures. Much species-specific knowledge is still lacking regarding responses to interactions, although from a management perspective, it seems easier to manage mixtures groupwise rather than stem-wise. Finally, we highlight high deer populations as perhaps the greatest challenge for mixed forest regeneration. More knowledge in the field and greater cooperation between researchers and different stakeholder groups are needed to solve this problem.
... For instance, endemic black pine old growth forests in central areas and pre-Pyrenees of Catalonia represent a good example of well adapted species to frequent surface fires (Fulé et al., 2008;Tíscar and Lucas-Borja, 2016). However, fire exclusion policies, poor forest-management practices (i.e., diametric cuts by just thinning the largest and the suitable trees for electric poles), and depletion of livestock transformed those forests into laddered fuel dense structures where high severity stand-replacing fires caused very substantial losses on past events (Martín-Alcón and Coll, 2016;Ordóñez et al., 2005). Thus, previous mechanical treatments and prescribed fires might be required to favor the resistance of remaining dominant seed trees before re-introducing the lightning fires. ...
Southern European countries rely largely on fire suppression and ignition prevention to manage a growing wildfire problem. We explored a more wholistic, long-term approach based on priority maps for the implementation of diverse management options aimed at creating fire resilient landscapes, restoring cultural fire regimes, facilitating safe and efficient fire response, and creating fire-adapted communities. To illustrate this new comprehensive strategy for fire-prone Mediterranean areas, we developed and implemented the framework in Catalonia (northeastern Spain). We first used advanced simulation modeling methods to assess various wildfire exposure metrics across spatially changing fire-regime conditions, and these outputs were then combined with land use maps and historical fire occurrence data to prioritize different fuel and fire management options at the municipality level. Priority sites for fuel management programs concentrated in the central and northeastern high-hazard forestlands. The suitable areas for reintroducing fires in natural ecosystems located in scattered municipalities with ample lightning ignitions and minimal human presence. Priority areas for ignition prevention programs were mapped to populated coastal municipalities and main transportation corridors. Landscapes where fire suppression is the principal long-term strategy concentrated in agricultural plains with a high density of ignitions. Localized programs to build defensible space and improve self-protection on communities could be emphasized in the coastal wildland-urban interface and inner intermix areas from Barcelona and Gerona. We discuss how the results of this study can facilitate collaborative landscape planning and identify the constraints that prevent a longer term and more effective solution to better coexist with fire in southern European regions.
... The persistence of this species is often threatened by its weak response to wildfires (Gracia et al., 2002;Ordoñez García, 2004;Retana et al., 2002;Rubiales et al., 2010), which could be due to its adaptive strategies, such as its non-serotinous cones (Lanner, 1998;Martín-Alcón and Coll, 2016) and the intolerance of the seeds to high temperatures (Escudero et al., 1997;Habrouk et al., 1999). We also assumed that treatments that included heavy thinning would have better natural regeneration than the ones that included light thinning. ...
Global change threatens the persistence of native forest ecosystems mainly by limiting the conditions for natural regeneration but also inducing tree mortality and increasing the risk of large wildfires. In this context, understanding the biotic and biotic factors that ultimately determine tree recruitment is of pivotal importance to implement adaptive
forest management strategies. In this study we assess how multipurpose management strategies, including combinations of thinning intensities and prescribed burning, affect the seed emergence and seedling survival of Pinus nigra Arn. subsp. salzmannii in two different forest sites in NE Spain. We tested four overstorey and fuel treatments that combined heavy and light intensity thinnings from below with understorey clearing and two different treatments of the resulting slash: prescribed burning and lop and scatter. The results showed: (1) a lack of regeneration in control units, probably caused by the high density of canopy and understorey; (2) greater seedling recruitment in units treated
with slash burning than in units treated with slash lop and scatter, probably due to the effects of prescribed burning on the herbaceous layer, soil organic layer, nutrient pools, and understorey; and (3) a different regeneration response between sites for treatments that included prescribed burning, probably due to microclimatic conditions during the
experiment and differences in the characteristics of the prescribed burns. These findings indicate the potential effectiveness of combined treatments of thinning and slash burning in the context of the implementation of multipurpose management actions in endangered ecosystems adapted to low intensity fires.
... More recently, object-based approaches to image processing that consider not only spectral data but also object size, shape and texture in relation to other objects in the image have shown strong potential for mapping burned-area extent (Dragozi et al. 2014;Lohberger et al. 2017). Object-based approaches could also be used to classify post-fire recovery, but are only starting to be developed (Mitri and Gitas 2013;Martín-Alcón and Coll 2016). ...
Interpretations of post-fire condition and rates of vegetation recovery can influence management priorities, actions and perception of latent risks from landslides and floods. In this study, we used the Waldo Canyon fire (2012, Colorado Springs, Colorado, USA) as a case study to explore how a time series (2011–2016) of high-resolution images can be used to delineate burn extent and severity, as well as quantify post-fire vegetation recovery. We applied an object-based approach to map burn severity and vegetation recovery using Worldview-2, Worldview-3 and QuickBird-2 imagery. The burned area was classified as 51% high, 20% moderate and 29% low burn-severity. Across the burn extent, the shrub cover class showed a rapid recovery, resprouting vigorously within 1 year, whereas 4 years post-fire, areas previously dominated by conifers were divided approximately equally between being classified as dominated by quaking aspen saplings with herbaceous species in the understorey or minimally recovered. Relative to using a pixel-based Normalised Difference Vegetation Index (NDVI), our object-based approach showed higher rates of revegetation. High-resolution imagery can provide an effective means to monitor post-fire site conditions and complement more prevalent efforts with moderate- and coarse-resolution sensors.
... Second, warmer and drier events would intensify neighborhood competition on pine performance, increasing the likelihood of competitive exclusion by oaks. As a consequence, the failure of direct regeneration and the negative effect of resprouters on late-established pines are expected to limit its ability to reach and overtop the resprouter-dominated canopy and thus, decrease the distribution of nonserotinous pines in the landscape at the expense of the overall expansion of resprouters (Martín-Alcón and Coll, 2016;Retana et al., 2002;Rodrigo et al., 2004). This will reduce forest functional diversity, and therefore their resistance and resilience to future combined disturbances (Sánchez-Pinillos et al., 2016). ...
The persistence of non-serotinous pines in Mediterranean forests can be threatened by climate-mediated changes in fire regimes that may favor the dominance of resprouters or other fire-adapted species. Recovery of non-serotinous pines after large wildfires is often determined by their ability to grow under the canopy of promptly established resprouters. Mechanisms of facilitation or competition between resprouters and pines will thus have a profound effect on forest dynamics. We examined here the effect of neighboring oak resprouts on Pinus nigra Arn. ssp. salzmannii saplings 18 years after a wildfire. We determined the net outcome of interactions between oaks and pines and how they vary with the life stage and size of the interacting plants or the environmental conditions. We did not find any net facilitative effects of oaks on pine sapling growth. The sensitivity of pines to neighbors varied markedly with pine size, and to a lesser extent, with water availability during the growing season. Our findings suggest a self-reinforcing hierarchical process by which early-dispersed seedlings growing in low-competitive microsites can grow faster, mitigating neighboring competition in the later stage of canopy closure. These results entail a potentially critical role of management practices to promote post-fire recovery of non-serotinous pines under expected changing conditions of disturbance regimes.
Context
Forest fires are key ecological factors affecting pine forests globally. Understanding impacts of varying fire intensities on forest ecosystem components is crucial for predicting recovery and informing management.
Objectives
This study aimed to assess effects of different surface fire intensities on structural components of pine forests, including tree canopy, herbaceous layer, and surface soil horizons, and identify relationships between fire intensity and ecosystem parameters.
Methods
The study examined three areas with different fire intensities (severe, moderate, mild) 1 year after a surface fire in Ukraine's Volyn-Polissia region, using vegetation surveys, soil analyses, and statistical methods.
Results
Fire intensity significantly influenced tree mortality and the vitality structure of Pinus sylvestris stands. Scorch height correlated strongly with stem diameter in mild and moderate intensity zones (P < 0.0001). Herbaceous layer composition showed significant variations in all life-form traits across different fire intensities. Species diversity, dominance, and evenness indices varied with fire intensity, as did species distribution by ecological strategies. Soil physicochemical properties, including surface layer density, ash content, moisture capacity, and pH, also changed. Correlations were found between the condition index of P. sylvestris and soil pH, as well as between herbaceous cover dominance/evenness indices and P2O5 content in surface soil layers. Weaker associations were identified between herbaceous cover diversity and soil density/hygroscopic moisture. The study was conducted over a 1-year period following the fire event, focusing on the short-term responses of vegetation and soil properties.
Conclusions
Surface fires of varying intensities alter multiple forest ecosystem components. Severely damaged areas may require restoration efforts, including active interventions such as artificial reforestation or other measures to accelerate recovery processes. Moderately and mildly affected zones, on the other hand, show potential for natural self-regulation. These findings have important implications for post-fire forest management strategies.
Ecosystem services (ES) in Mediterranean regions are critically affected by forest fires, which pose significant threats to human reliance on these services. This study delves into the post-fire dynamics of ES, emphasising the distinct recovery processes in seeders dominated and resprouters dominated systems. By integrating an ecosystem service capacity matrix with transition matrices, we analysed the temporal recovery patterns of ES after fire disturbances under conditions corresponding to southern France Mediterranean-Type Ecosystems. In seeders dominated environments, recovery is gradual, with services like carbon sequestration and soil quality taking up to 87 years to regain 90% of their capacity post-high-intensity fires. Conversely, resprouters dominated systems show rapid regrowth, with carbon sequestration recovering in as little as 23 years following similar disturbances. Our findings highlight the variable recovery timelines across different ES. Pollination and wild plants display remarkable resilience, with recovery times not exceeding 2 years regardless of fire severity. However, provisioning services such as game provision exhibit lower resilience, requiring up to 67 years for recovery. Cultural services, reflecting emblematic and symbolic values, demonstrate greater resilience, with recovery spanning 3 to 51 years. This study underscores the importance of understanding vegetation types and succession patterns in predicting ES recovery post-fire, offering insights into ecosystem recovery and resilience in fire-prone Mediterranean landscapes.
Background
Climate change is altering the fire regime and compromising the post-fire recovery of vegetation worldwide. To understand the factors influencing post-fire vegetation cover restoration, we calculated the recovery of vegetation in 200,000 hectares of western Mediterranean forest burned by 268 wildfires over a 27-year period (1988–2015). We used time series of the Tasseled Cap Transformation Brightness (TCTB) spectral transformation over Landsat imagery to calculate vegetation recovery. Then, we quantified the importance of the main drivers of post-fire vegetation recovery (climate, fire severity, and topography) along an aridity gradient (semi-arid, sub-humid, and humid) using Random Forest models.
Results
In most models (99.7%), drought duration was the most important factor, negatively affecting post-fire recovery especially in the extremes of the aridity gradient. Fire severity was the second most important factor for vegetation cover recovery, with its effect varying along the aridity gradient: there was a positive relationship between fire severity and recovery in sub-humid and humid areas, while semi-arid areas showed the opposite pattern. Topographic variables were the least important driver and had a marginal effect on post-fire recovery. Additionally, semi-arid areas exhibited a low mean recovery rate, indicating limitations in the short-term recovery after a fire.
Conclusions
Our study highlights the key role that drought duration plays in the recovery of vegetation after wildfires in the Mediterranean basin and, particularly, in forests located in climatically extreme areas. The results suggest that the predicted increase in drought duration coupled with a higher frequency and intensity of large fires may modify the structure and composition of Mediterranean forest ecosystems. Our analysis provides relevant information to evaluate and design adaptive management strategies in post-fire recovery hotspots of Mediterranean forest ecosystems.
La dinámica que siguen la estructura y diversidad de la vegetación en un sitio después de sufrir un disturbio es un indicador de la resiliencia del ecosistema afectado. En este estudio se analizaron la composición florística y los cambios en la sucesión vegetal de acuerdo con la cronosecuencia de diferentes disturbios, en un bosque de pino-encino del Sur de Oaxaca, México. Se usó un muestreo selectivo estableciendo 28 sitios de muestreo de 400 m2, en los cuales se realizó un censo de todos los individuos vasculares durante las temporadas de estiaje y lluvias de 2018. Se estimaron y analizaron la diversidad alfa y la beta, así como la estructura vertical y horizontal en todas las cronosecuencias: 1) incendios (IF) ocurridos hace un año (IF-1), cinco años (IF-5) y seis años (IF-6); 2) tierras de cultivo con descanso agrícola (DA) de ocho años (DA-8) y 20 años (DA-20); 3) libre pastoreo (PA) y 4) una zona de referencia, sin intervención (C1). La mayor riqueza (89) se registró durante la temporada de lluvias (F = 0.0154) en un área con descanso agrícola durante 20 años. En el área con incendio ocurrido un año antes se observó la diversidad más baja: Shannon = 1.26 y Shannon = 1.60 en ambas temporadas. El índice de valor de importancia más alto (86.55%) fue calculado para Pinus lawsonii Roezl en el área con incendio ocurrido seis años atrás. El disturbio ocasionado por fuego fue el que causó mayor daño a la estructura y diversidad de la vegetación, sin embargo, también fue en el que la vegetación reapareció en menor tiempo. La composición florística varió de acuerdo con el tipo, severidad y tiempo transcurrido después del disturbio, mientras que la riqueza de especies se relacionó con la estructura vegetal en el sitio, que determina las condiciones microambientales. Los resultados son útiles para la aplicación de medidas de restauración y conservación.
El proyecto LIFE ADAPT-ALEPPO (2021-2025), tiene como principal objetivo el desarrollo de nuevas herramientas para la adaptación de los bosques ibéricos de pino carrasco (subtipo 42.841 del Hábitat 9540 de la Directiva Hábitats, Anexo I) al cambio climático, así como su aplicación demostrativa. Estas herramientas se centrarán en la detección temprana de los procesos de decaimiento y en la mejora de la resiliencia de este ecosistema mediante el aumento de su vigor, su capacidad de adaptación a la aridificación climática y la capacidad de recuperar sus funciones tras las perturbaciones naturales. El alcance geográfico del proyecto abarca el área potencial de distribución del subtipo en la Península Ibérica, incluyendo las vertientes mediterráneas de las montañas catalanas y del Sistema Ibérico, la cuenca del Ebro y las cordilleras prebéticas. En este trabajo se describen las principales acciones a ejecutar en el proyecto LIFE.
Balzan MV, Hassoun AER, Aroua N, Baldy V, Bou Dagher M, Branquinho C, Dutay J-C, El Bour M, Médail F, Mojtahid M, Morán-Ordóñez A, Roggero PP, Rossi Heras S, Schatz B, Vogiatzakis IN, Zaimes GN, Ziveri P 2020 Ecosystems. In: Climate and Environmental Change in the Mediterranean Basin – Current Situation and Risks for the Future. First Mediterranean Assessment Report [Cramer W, Guiot J, Marini K (eds.)] Union for the Mediterranean, Plan Bleu, UNEP/MAP, Marseille, France, pp. 323-468.
Pine species are dominant in a large part of the western Mediterranean landscapes where they provide a wide range of goods and services. At present, the different components of global change threaten the delicate equilibrium between the current structure and functioning of most of these pinewoods and the future provision of ecosystem services required by human societies. In this chapter, we briefly review the origin of these systems and the main biotic and abiotic drivers of their current dynamics. We put particular emphasis on the factors modulating survival and growth at early growth stages, which are the most vulnerable to environmental uncertainty. In addition, we highlight the importance of natural diversification processes for the resilience of these systems to natural disturbances and we revise the main silvicultural models and treatments that are applied for the execution of different management objectives. Finally, we underline the need to move towards management schemes oriented to the enhancement of the adaptive capacity of these forests to climate change.
A long history of human influence, including large-scale afforestation with pines and changes in land-management and conservation priorities, have strongly affected the formation of Mediterranean landscapes with contiguous patches of pine stands and oak woodlands. Consequently, this pine-oak mosaic creates opportunities for cross-colonization of both species and the formation of mixed pine-oak forests. These processes are homologous to classical secondary succession in which abandoned agricultural land is colonized by early-successional pines, which allow the establishment of late-successional oaks. We used the frameworks of forest succession and gap dynamics to explore the evidence for pine and oak regeneration within mixed pine-oak forests, and evaluate the fate of these Mediterranean mixed forests. Our analysis highlights selection towards enhanced oak regeneration and recruitment and lowered survival and recruitment for pines within mixed pine-oak forests, which is expected to drive succession from the intermediate mixed stage towards late-successional oak-dominated forest. However, studies have proposed persistence mechanisms for the maintenance of mixed pine-oak forests as a long-term stable stage, in which gaps form in the mixed forest of pines and oaks, allowing the recruitment of both species. Alternatively, scenarios of novel climates or fire regimes have projected a deterioration of developed forests to vegetation formations dominated by non-tree forms.
We discuss the environmental, social, and technological trends that will influence fire science and management in the coming decades. We begin by discussing the influence of global change, including climate and social changes, on how fires burn, our perceptions of wildland fire, and how we respond to fires. We highlight several of these challenges using the exceptional 2019–2020 wildfire season in Australia. Next, we discuss technological trends related to data collection, data analysis, and simulation that are transforming fire science and management. We end the chapter by discussing the integration of fire science with management, and the training and education of current and future fire professionals. As this is the last chapter of our book, Fire Science from Chemistry to Landscape Management, we hope that the concepts, ideas, and trends discussed provide the foundation for groundbreaking research and sustainable fire management that will guide us into the future.
Despite covering only 0.82% of the ocean’s surface, the Mediterranean Sea supports up to 18% of all known marine species, with 21% being listed as vulnerable and 11% as endangered. The acceler- ated spread of tropical non-indigenous species is leading to the “tropicalization” of Mediterranean fauna and flora as a result of warming and extreme heat waves since the 1990s. The acidification rate in the Mediterranean waters has ranged between 0.055 and 0.156 pH units since the pre-industrial period, affecting the marine trophic chain, from its primary producers (i.e., coccolithophores and fo- raminifera) to corals and coralline red algae.
Projections for high emission scenarios show that endemic assemblages will be modified with numerous species becoming extinct in the mid 21st century and changes to the natural habitats of commercially valuable species, which would have many repercussions on marine ecosystem services such as tourism, fisheries, climate regulation, and ultimately on human health.
Adaptation strategies to reduce environmental change impacts need effective mitigation policies and actions. They require anticipatory planning to enable them to tackle problems while they are still manageable. Given the diversity of each Mediterranean sub-basin, wider monitoring coverage is needed to strengthen our knowledge about the different adaptation processes that characterize and best suit each geographical zone. Adaptation implies the implementation of more sustainable fishing practices as well as reducing pollution from agricultural activity, sustainable tourism or developing more effective waste management. Marine protected areas can potentially have an insurance role if they are established in locations not particularly vulnerable to ocean acidification and climate change.
Post-fire environmental conditions can heavily influence the natural regeneration of pine species in Mediterranean forests. Therefore, enhancing post-fire recovery of pine species is fundamental for effective ecological restoration of Mediterranean forests. In this study, the effects of a post-fire restoration treatment on the seedling emergence and survival of Spanish black pine (Pinus nigra Arn. ssp salzmannii) were investigated under a treatment consisting of manual cut of burnt tree canopies placed on the soil surface with their tree branches, following contour lines (contour-felled log debris, CFD) in comparison with a control site at plot scale. Both CFD and control plots were tested on three slope gradients and two experimental conditions, i.e. protected vs. non protected seeds. The initial seedling recruitment of Spanish black pine was improved by CFD treatment and seed protection, specifically through increased survival of emergent seedlings by about ten and fifteen times, respectively, compared to control. Seedling emergence was not significantly different between the treatments or controls; however, the highest seedling emergence in the study (18.9 ± 14.9%) was recorded under the least severe drought conditions. The study demonstrates that post-fire CFD and seed protection treatments can be favourable for supporting ecological restoration of these pine forests. However, the environmental conditions are important drivers for the success of these strategies. Since droughts are expected to be more frequent in the upcoming years, post-fire management strategies that include treatments like CFD and seed protection can be useful in the ecological restoration of Mediterranean pine forests.
Keywords: Seedling emergence; seedling survival; wildfire; Mediterranean forest;
post-fire ecological restoration; contour-felled log debris.
Mediterranean Ecosystem report on Climate and Global changes.
Balzan MV, Hassoun AER, Aroua N, Baldy V, Bou Dagher M, Branquinho C, Dutay
J-C, El Bour M, Médail F, Mojtahid M, Morán-Ordóñez A, Roggero PP, Rossi Heras S, Schatz B, Vogiatzakis IN, Zaimes GN, Ziveri P 2020 Ecosystems. In: Climate and Environmental Change in the Mediterranean Basin – Current Situation and Risks for the Future. First Mediterranean Assessment Report [Cramer W, Guiot J, Marini K (eds.)] Union for the Mediterranean, Plan Bleu, UNEP/MAP, Marseille, France, 151pp, in press
Marine ecosystems:
Despite covering only 0.82% of the ocean’s surface, the Mediterranean Sea supports up to 18% of all known marine species, with 21% being listed as vulnerable and 11% as endangered. The accelerated spread of tropical non-indigenous species is leading to the “tropicalization” of Mediterranean fauna and flora as a result of warming and extreme heat waves since the 1990s. The acidification rate in the Mediterranean waters has ranged between 0.055 and 0.156 pH units since the pre-industrial period, affecting the marine trophic chain, from its primary producers (i.e., coccolithophores and foraminifera) to corals and coralline red algae. Projections for high emission scenarios show that endemic assemblages will be modified with numerous species becoming extinct in the mid 21st century and changes to the natural habitats of commercially valuable species, which would have many repercussions on marine ecosystem services such as tourism, fisheries, climate regulation, and ultimately on human health. Adaptation strategies to reduce environmental change impacts need effective mitigation policies and actions. They require anticipatory planning to enable them to tackle problems while they are still manageable. Given the diversity of each Mediterranean sub-basin, wider monitoring coverage is needed to strengthen our knowledge about the different adaptation processes that characterize and best suit each geographical zone. Adaptation implies the implementation of more sustainable fishing practices as well as reducing pollution from agricultural activity, sustainable tourism or developing more effective waste management. Marine protected areas can potentially have an insurance role if they are established in locations not particularly vulnerable to ocean acidification and climate change.
Coastal ecosystems:
The coastal zone, i.e. the area in which the interaction between marine systems and the land dominate ecological and resource systems, is a hotspot of risks, especially in the south-eastern Mediterranean region. Alterations to coastal ecosystems (lagoons, deltas, salt marshes, etc.) due to climate change and human activities affect the flow of nutrients to the sea, the magnitude, timing and composition of potentially harmful/toxic plankton blooms. They also significantly increase the number and frequency of jellyfish outbreaks, and could have negative impacts on fisheries. 1.2 to 5% of seagrass meadows in the Mediterranean Sea, which represent 5 to 17% of the worldwide seagrass habitat, are lost each year. Among them, almost half of the surveyed Posidonia oceanica sites have suffered net density losses of over 20% in 10 years. As for fish, non-indigenous species and climate change cause local extinction. Projected temperature increases combined with a decrease in nutrient replenishment and ocean acidification, are expected to cause changes in plankton communities, negative impacts on fish, corals, seagrass meadows and propagation of non-indigenous species. Projected sea level rise will impact coastal wetlands deltas and lagoons. Extensive urbanization added to climate change is also expected to threaten coastal ecosystems, human health and well-being. A nexus approach is required when trying to establish adaptation methods for the entire Mediterranean, while taking into account ecosystem-based management, synergies and conflicts, integrating local knowledge and institutions. Suitable adaptation policies include reducing pollution runoff, both from agriculture and industry and waste management, and policies to limit or prevent acidification. Conservation planning and management should focus on cross-cutting approaches and building resilience between structural and functional connectivities of various fields.
Terrestrial ecosystems:
Biodiversity changes in the Mediterranean over the past 40 years have occurred more quickly and been more significant than in other regions of the world. Urbanization and the loss of grasslands are key factors of ecosystem degradation across the region. Since 1990, agricultural abandonment has led to a general increase in forest areas in the northern Mediterranean, while in the southern Mediterranean, ecosystems are still at risk of fragmentation or disappearance due to human pressure from clearing and cultivation, overexploitation of firewood and overgrazing. Drylands have significant biodiversity value, with many of the plants and animals highly adapted to water-limited conditions. They are undergoing an overall increase in response to climate change and extensive land abandonment. 48% of Mediterranean wetlands were lost between 1970 and 2013, with 36% of wetland-dependent animals in the Mediterranean threatened with extinction. Because of the reduction in river flows, 40% of fish species in Mediterranean rivers are endangered. Projections for the 21st century indicate drier climate and increased human pressure, with negative impacts on terrestrial biodiversity, forest productivity, burned areas, freshwater ecosystems and agrosystems. Future projections indicate that burnt areas can increase across the region by up to 40% in a 1.5°C warming scenario and up to 100% from current levels for 3°C warming at the end of the century. Mediterranean drylands will become drier and their extent is expected to increase across the region. Projections suggest decreased hydrological connectivity, increased concentration of pollutants during droughts, changes in biological communities as a result of harsher environmental conditions, and a decrease in biological processes such as nutrient uptake, primary production, and decomposition. Promotion of ‘climate-wise connectivity’ through permeability of the landscape matrix, dispersal corridors and habitat networks are key to facilitating upward the migration of lowland species to mountains in order to adapt to new climate change conditions. Promotion of mixedspecies forest stands and sylvicultural practices such as thinning, and management of understory can promote the adaption of Mediterranean forests to climate change. Promotion of the spatial heterogeneity of the landscape matrix can help reduce fire impacts. The preservation of the natural flow variability of Mediterranean rivers and streams and wide riparian areas, along with reductions in water demand are key to the adaptation of freshwater ecosystems to future climate change.
Wildfires trigger changes in vegetation dynamics if the existing community does not resist the fire and succumbs. However, the same vegetation state may still occur if populations show post-fire resilience, that is, if they are able to regenerate after fire. Such regeneration will be a function of interactions between propagule availability (aerial or soil seed banks or other seed sources nearby), its establishment success (dependent on soil resources, dormancy break, herbivores, and microsite conditions), fire recurrence, and mycorrhizal networks. When pre-fire species fail to survive and regenerate after the fire, changes in the vegetation state may lead to either a forested or a deforested state, depending on legacies from the previously established community, climatic conditions and water balance, and other processes. Climate change may compromise post-fire state changes when newly established communities cannot survive under the novel environmental conditions expected for the end of this century. Here we review overall post-fire vegetation changes, with a particular emphasis on Mediterranean environments.
Wildfires play a major role in driving vegetation changes and can cause important environmental and economic losses in Mediterranean forests, especially where the dominant species lacks efficient postfire regeneration mechanisms. In these areas, postdisturbance vegetation management strategies need to be based on detailed, spatially continuous inventories of the burned area. Here, we present a methodology in which we combine airborne LiDAR and multispectral imagery to assess postfire regeneration types in a spatially continuous way, using a Mediterranean black pine (Pinus nigra Arn ssp. salzmannii) forest that burned in 1998 as a case study. Five postfire regeneration types were obtained by clustering field-plot data using Ward’s method. Two of the five regeneration types presented high tree cover (one clearly dominated by hardwoods and the other dominated by pines), a third type presented low to moderate tree cover, being dominated by hardwoods, and the remaining two types matched to areas dominated by soil–herbaceous or shrub layers with very low or no tree cover (i.e., very low to no tree species regeneration). These five types of regeneration were used to conduct a supervised classification of remote sensing data using a nonparametric supervised classification technique. Compared with independent field validation points, the remote sensing based assessment method resulted in a global classification accuracy of 82.7%. Proportions of regeneration types in the study area indicated a general shift from the former pine-dominated forest toward hardwood dominance and showed no serious problems of regeneration failure. Our methodological approach appears to be appropriate for informing postdisturbance vegetation management strategies over large areas.
This study relates the spatial variability in tree regeneration generated by fire with topography and pre-fire vegetation composition, and analyses how the pattern of fire severities determines post-fire regeneration of the dominant tree species (Pinus halepensis and Quercus ilex) in a large fire that occurred in north-eastern Spain in summer 1994. At the fire level, the proportion of the different fire severities in the burned area was characteristic of large fires that burn with high severity. At the level of plot, the variability of fire severity in the study site depended on two topographic characteristics: elevation and aspect. Plots burned with high fire severity were distributed at higher altitude than less severely burned plots, which were mainly distributed in south- and east-facing slopes. Fire severity also increased with Q. ilex density in the stand. The mosaic of fire severities determined both plant mortality and seedling regeneration. Mortality of stems caused by fire was very high in both species, but many Q. ilex individuals resprouted after fire. Seedling regeneration of P. halepensis showed large differences among plots in the burned area, reflecting large spatial variability due to the elevation gradient, the variation in density of adult pine trees, and the spatial variability created by fire.
Tree recruitment is a key process underlying stand dynamics and sustainability in managed forests. Woody plant cover is known to affect the regeneration success of Pinus nigra, suggesting the existence of facilitative plant-plant interactions. The regeneration patterns of this Mediterranean pine were analyzed across its distribution area, using data from 3226 plots of the Spanish National Forest Inventory. We aimed to test the hypothesis that seedlings establishment occurs under higher values of either canopy or shrub cover in the driest populations, as predicted by the stress-gradient hypothesis. Data were analyzed by means of Generalized Linear Models and multivariate methods. Results revealed that regeneration failure occurs on a regional scale, and that regeneration is facilitated by tree canopy cover of 55%–80%. A non-linear pattern of interaction along an aridity gradient was identified, with competition at the wettest site, high facilitation at the mid-dry sites, and low facilitation at the driest site. Evidence suggests that some shrub species may facilitate recruitment in the harsher areas. Collectively, our results reduce the possibilities of adapting forest management to drying climates by the application of alternative silvicultural prescriptions involving canopy cover.
Most of the world's plantations were established on previously disturbed sites with an intensive land-use history. Our general hypothesis was that native forest regeneration within forest plantations depends largely on in situ biological legacies as a source of propagules. To test this hypothesis, we analyzed native oak regeneration in 168 pine plantation plots in southern Spain in relation to land use in 1956, oak patch proximity, and pine tree density. Historical land-use patterns were determined from aerial photography from 1956, and these were compared with inventory data from 2004-2005 and additional orthophoto images. Our results indicate that oak forest regeneration in pine plantations depends largely on land-use legacies, although nearby, well-conserved areas can provide propagules for colonization from outside the plantation, and pine tree density also affected oak recruit density. More intense land uses in the past meant fewer biological legacies and, therefore, lower likelihood of regenerating native forest. That is, oak recruit density was lower when land use in 1956 was croplands (0.004 +/- 0.002 recruits/m2 [mean +/- SE]) or pasture (0.081 +/- 0.054 recruits/m2) instead of shrubland (0.098 +/- 0.031 recruits/m2) or oak formations (0.314 +/- 0.080 recruits/m2). Our study shows that land use in the past was more important than propagule source distance or pine tree density in explaining levels of native forest regeneration in plantations. Thus, strategies for restoring native oak forests in pine plantations may benefit from considering land-use legacies as well as distance to propagule sources and pine density.
Introduction
Pinus is a diverse genus of trees widely distributed throughout the Northern Hemisphere. Understanding pine life history is critical to both conservation and fire management.
Objectives
Here I lay out the different pathways of pine life history adaptation and a brief overview of pine evolution and the very significant role that fire has played.
Results
Pinus originated ~150 Ma in the mid-Mesozoic Era and radiated across the northern continent of Laurasia during the Cretaceous Period. Pines have followed two evolutionary strategies interpreted as responses to competition by the newly emerging angiosperms. The Strobus lineage mostly has radiated into stressful sites of low nutrient soils and extremes in cold or heat. The Pinus (subgenus) lineage has radiated into fire-prone landscapes with diverse fire regimes. Examination of life history traits illustrates syndromes associated with fire-avoider, fire-tolerater, fire-embracer, and fire-refuge strategies.
Conclusion
Understanding the current pattern of pine distribution requires interpreting their evolution in terms of climate, geology, and fire. All three of these factors have played a role since the Mesozoic origin of the genus. All are important to the appropriate management of these resources.
Quercus forest regeneration is limited by different factors, post-dispersal predation being one of the most critical stages. We analysed seed removal of four coexisting Quercus species (Q. ilex, Q. suber, Q. faginea and Q. pyrenaica) in a Mediterranean forest located in Southern Spain. Marked and weighed acorns from each of the species were placed in experimental units with or without exclusion of large herbivores and in two microhabitat types (Q. ilex shade or open). Acorn removal was monitored for 120 days in order to test the effect of exclusion of large herbivore and microhabitat type on seed removal rates and species selection. Interestingly, the results of microhabitat and species selection differed depending on the presence of large herbivores. Removal was faster in sites without exclusion, where most seeds (≈85%) disappeared during the first 9 days. In these sites, no differences in seed removal were found between different microhabitats, but seeds of two species, those with higher seed mass (Q. suber and Q. pyrenaica) were most preferred. However, under exclusion of large herbivores, seed removal was affected by the microhabitat, this being greater in Q. ilex shaded microhabitats, which showed a higher structural diversity. Also, species selection was completely different under exclusion of large herbivores, and seeds of Q. ilex and Q. faginea were removed faster. These results highlight the importance of large herbivore activity on seed removal and its effect on microhabitat and species selection. Therefore, specific selection by seed consumers may modify seedling recruitment and may have an important influence on the relative abundance of coexisting Quercus species.
For millennia, mankind has shaped landscapes, particularly through agriculture. In Europe, the age-old interaction between humans and ecosystems strongly influenced the cultural heritage. Yet European farmland is now being abandoned, especially in remote areas. The loss of the traditional agricultural landscapes and its consequences for biodiversity and ecosystem services is generating concerns in both the scientific community and the public. Here we ask to what extent farmland abandonment can be considered as an opportunity for rewilding ecosystems. We analyze the perceptions of traditional agriculture in Europe and their influence in land management policies. We argue that, contrary to the common perception, traditional agriculture practices were not environmentally friendly and that the standards of living of rural populations were low. We suggest that current policies to maintain extensive farming landscapes underestimate the human labor needed to sustain these landscapes and the recent and future dynamics of the socio-economic drivers behind abandonment. We examine the potential benefits for ecosystems and people from rewilding. We identify species that could benefit from land abandonment and forest regeneration and the ecosystem services that could be provided such as carbon sequestration and recreation. Finally, we discuss the challenges associated with rewilding, including the need to maintain open areas, the fire risks, and the conflicts between people and wildlife. Despite these challenges, we argue that rewilding should be recognized by policy-makers as one of the possible land management options in Europe, particularly on marginal areas.
Regeneration of ponderosa pine after fire depends on the patterns of seed availability and the environmental conditions that define safe sites for seedling establishment. A transect approach was applied in 2002 to determine the spatial distribution of regeneration from unburned to burned areas within the landscape impacted by the Jasper Fire of 2000 in the Black Hills of South Dakota (USA). Canopy conditions alone, reflecting seed availability, at the stand level were not correlated with regeneration success. However, canopy conditions in combination with ground conditions ex- plained patterns of regeneration success at the plot level ( 2m×6m scale), and ground conditions explained these pat- terns at the quadrat level (0. 2m×0 .2 ms cale).Only at the finer level of the quadrat could environmental factors explain seedling survival. Safe sites were characterized, in part, by the presence of scorched needle litter on blackened mineral soil. Areas with high understory cover restricted regeneration in the undisturbed forest and reduced seedling survival in the burned areas. The description of environmental conditions that favor and discourage ponderosa pine regeneration success will improve our understanding of how environmental heterogeneity within burned areas will contribute to the future forested landscape.
Aim of the study: The aim of the research is to analyse the role of Quercus ilex advance regeneration in the stand regeneration of pine plantations after small-sized canopy openings, and to assess the influence of the forest stand and the canopy opening. The performance of the advance regeneration under the pine plantation is also examined.
Area of study: A Pinus nigra plantation in dry Continental Mediterranean climate in eastern Spain.
Materials and Methods: The tree regeneration of ten canopy openings of 0.17-0.43 ha was monitored during five years after treatment. It was also sampled in 0.12 ha-plots in the non-treated pine plantation surrounding the openings.
Main results: An important increase in the height of Q. ilex regeneration was observed in the openings, unlike what was found in the intact pine plantation. In the pine plantation, stand density showed a moderate positive influence on the density of Q. ilex regeneration, whereas in the canopy gaps Q. ilex height was negatively influenced by stand density before the opening.
Research highlights: The canopy opening triggered a response in Q. ilex advance regeneration, although height growth rates seemed to reduce over time. The results support the view that promoting Q. ilex in pine plantations may require different management strategies depending on the characteristics of the pine overstorey and on the density and size of the advance regeneration.
ABSTRACT Understanding the processes of tree population recruitment and their limitations, is the scientific basis to assure the forest natural regeneration, and to improve techniques of restoration and afforestation. We present here preliminary,results of a collaborative project (HETEROMED). The environmental heterogeneity,of Mediterranean forests was related to natural,patterns,of seedling,establishment. Factorial design experiments,of seed,addition,were carried out and,the resulting emergence,and survival were related to the conditions of light and,soil moisture. The fieldwork,was,carried out at two natural areas in South Spain: Sierra Nevada,NationalPark (higher mountains,on the Southeast) and Los Alcornocales Natural Park (lower mountains in Sierra del Aljibe range, on the southern tip of the Iberian Peninsula). The experiments were focussed in seven target species - Quercus suber, Quercus canariensis, Quercus ilex, Quercus pyrenaica, Pinus sylvestris, Acer granatense and Sorbus aria. In addition, a glasshouse factorial experiment,investigated,the differential response,of the four Quercusspecies,to the combined,effects of shade and drought. In both field sites (Sierra Nevada and Sierra del Aljibe) seedling emergence differed among species, but was not significantly affected by habitat (light availability). In Sierra Nevada, seedling survival after dry summer was statistically different betweentree species, habitat type and irrigation treatment. Summer drought was the main cause of seedling,mortality. Survival was,higher,in deep shade,habitats,than,in open stands. Irrigation boosted survival in open areas (full light) and under shrublands (medium shade), but had scant effect inside woodland stands (deep shade). In Sierra del Aljibe, there were significant differences in seedling survival of Quercus suberbetween habitat types. Most surviving,seedlings after the dry summer,were,in habitats with medium,shade,(under tree canopy), rather than in full light (open areas) or deep shade (closed forest) habitats. In the glasshouse study, the seedling mass (after six months of growth) was statistically different between species, and between light and water treatments. In the deep,shade treatment,seedling mass was,not affected by stopping,irrigation (simulating seasonal drought), unlike in the full light. Acomparison,of field,and,glasshouse,results is carried out. A conflict,between,components,of regeneration
Land cover mapping obtained from photointerpretation of aerial photographs and orthophotographs was used to quantify land cover changes between 1957 and 1996 in a Mediterranean middle mountain area. Expansion of forested area is clearly the main land cover change caused by the abandonment of traditional agricultural activities and by the use of other materials and energy sources instead of forest resources. As a result, about 64% of the area was covered by forest by 1996, whereas in 1957 forests accounted for only 40% of the land cover. Spontaneous afforestation of abandoned fields with Scots pine (Pinus sylvestris L.) in terraced areas and areas of sparse scrub vegetation, coupled with an increase in the density of forest canopies, has been responsible for this expansion of woodland. The influence of physiographic factors in land cover change processes in the terraced areas of the catchment was also considered. The results demonstrate that within the terraced areas, north-facing and more elevated steeper slopes are more intensely afforested. However, an accurate analysis of the role played by these factors in land cover change cannot be carried out because the pattern of land abandonment is not independent of these physiographic characteristics. Furthermore, field observations at the terrace scale are evidence of the relevant influence of local topography in afforestation dynamics.
Succession of chaparral shrubs was studied for the first 4 years after fire on the four major slope faces at three elevations in southern California. Although total cover fluctuated from year to year, shrub cover increased annually through the third year. There was little or no increase in shrub cover between the third and fourth years. Four years after fire the shrubs covered 55% ground surface at the highest elevation site but only 28% at the lowest elevation site. Shrub cover was similar between slope faces with one exception; at the lowest elevation site shrub cover was twice as great on the north and east-facing slopes as on the south and west-facing slopes. Post-fire recovery of shrubs was by seedlings and/or resprouts. Yucca whipplei was an exception in that it did not resprout once the aboveground parts were killed nor did seedlings establish after fire, however the aboveground parts of many Y. whipplei survived the fire. Species which reproduced entirely by seed did so in the first post-fire year from soil-stored seed with the exception of Ceanothus greggii at the highest elevation site. This species was entirely absent the first year after fire but abundant in the second year. Species producing both resprouts and seedlings varied from site to site in the proportion of resprouts:seedlings. Between 83–100% of the post-fire populations of Cercocarpus betuloides, Arctostaphylos glandulosa, and Xylococcus bicolor were resprouts whereas 12–13% of Ceanothus tomentosus were resprouts. For Adenostoma fasciculatum, resprouts constituted 27–54% of the population at the lowest elevation and 65–94% at the highest elevation; whereas, the Quercus dumosa population was 100% resprouts at the lowest elevation and 31–67% resprouts at the highest elevation. Data are presented on the height of resprouts and seedlings for all species at the end of the first post-fire year.
This study presents a silvogenetic typology of single-species stands of Pinus nigra in Catalonia (NE of Spain) based on the information supplied by the Second National Forest Inventory. Results of factor analysis applied to dendrometric variables show nine different stand types, identified mainly from variables related to diameter distribution and stand stocking. The character of uneven-aged stands, present in five of the groups though with different features, was analyzed using a truncated Weibull distribution. The typology, which is managed by computing regeneration levels and diametric classes, encompasses different developmental stages and allows the diagnosis of compromised situations in terms of stand persistence caused by low or high stocking.
This chapter analyzes the post-fire management of non serotinous pine forests. These pine species do not regenerate after fire and depend on the arrival of seeds from the unburned vegetation to recover after wildfires. The chapter starts with an overview of the ecological context of these forests, from their distribution, vegetation composition and importance to their response after fire. Then it introduces the main issues and alternatives of post-fire management, and concludes with two case studies, one in the western and the other in the eastern Mediterranean Basin.
Pinus nigra subsp. salzmannii is a pine species that regenerates quite well under its own canopy but has difficulty regenerating after fire. This study analyzes, by means of greenhouse and field experiments, the pattern of seed germination and seedling establishment of P. nigra in a gradient of post-fire environmental conditions. The results obtained in the controlled conditions experiment of cover effects in the absence of vegetation interference indicate that seed germination and seedling survival and growth of P. nigra attained their maximum values under high cover levels. In the field, seed germination and seedling survival of P. nigra were considerably lower than in the experiment outdoors but also followed to a large extent the cover gradient. However, there were differences among microhabitats depending on the type of vegetation present. In general, the behaviour of P. nigra is more similar to that of shade-tolerant species, such as oaks, than to low-altitude Mediterranean pines, because the establishment of P. nigra seedlings is improved under high cover conditions. As these conditions are usually lacking in recently burned areas, the regeneration of this species is strongly limited after fire. The difficulty in recovering after fire of P. nigra forests confirms that they require specific conservation measures to prevent their disappearance in the short term.
Fire has favored pines throughout their natural range in environments subject to continuous disturbances, such as the Mediterranean Basin. However, recovery of pine species after large fires is not always successful. In this study, we analyze the post-fire regeneration pattern of Pinus halepensis, P. nigra and P. sylvestris three years after fire, in an area affected by a large wildfire in 1994. Moreover, we develop a model of succession to predict medium-term changes in forest composition 30 years after fire from the regeneration monitored during the first years after fire. The results show that, although the three pine species regenerate quite well in the absence of fire, their post-fire regeneration is very different: P. halepensis shows high seedling density after fire, but P, nigra and P, sylvestris almost dissapear from burned plots. The model simulations of the future forest composition 30 years after fire indicate that 77-93% of plots dominated by these two pines change after fire to communities dominated by oaks (Quercus ilex, Q. cerrioides). There is also a considerable number (7-16%) of these burned pine plots that change to shrublands. Thus, these observational and modelling results suggest that large fire events, which have increased considerably in the Mediterranean region in the last decades, may decrease the overall distribution of these pine species, especially that of P, nigra and P, sylvestris.
A major challenge for foresters in the future will be issues related to global change. Global change expresses itself in a variety of ways, depending on regional vegetation and climate patterns, small-scale topographic differences, tree species, and stand development stages. Using silviculture as an example, the variety of steps linking global change-as a general concept-and actual management decisions is explored. The first task is to relate global change aspects to silviculturally relevant scales. Second, silvicultural responses must reflect the wide variety of changes, including their interactions. A number of management recommendations have been proposed from the global scale to the application of specific silvicultural treatments. These recommendations are mostly focused on increasing the resistance of forests to perturbations. Increasing ecosystem adaptability and resilience through silvicultural practices may benefit from developments in other scientific fields. Recent advances in the complexity and ecosystem sciences may provide approaches that are better suited for a future with increased variability and uncertainty in ecological and social conditions. Specifically, managing forests as complex adaptive systems may provide a conceptual framework that can be useful for silviculture, even though much work still must be done to fully explore the implications of such a new framework for silvicultural decisionmaking.
Resprouting, i.e. the production of sprouts from buds on pre-existing plant organs, is one of the most important mechanisms of plant regeneration under natural and anthropogenic disturbances. This response has been widely observed in many plant communities around the world, but it is probably in Mediterranean regions that it has received most attention (Keeley and Zedler 1978). In fact, the resprouting ability of many Mediterranean shrubs and trees has been one of the most important keystones to building up the paradigm of the resilience (sensu Westman 1986) and autosuccessional nature (Hanes 1971) of these communities after disturbances. However, the evolutionary meaning and the selection forces that lead to the resprouting habit have been the focus of a long controversy. Since fire is one of the most typical disturbances in Mediterranean areas, and resprouting is a common response to fire, early studies pointed out that it was an adaptation, a trait selected by fire (Naveh 1974). Recent reviews have criticized this concept arguing that: (1) resprouting is an old and widespread trait among many angiosperm species, present in taxa not regularly exposed to fire (Axelrod 1989); and (2) other selective factors, such as grazing or drought, may also lead to a re-sprouting habit (James 1984; Keeley 1986). Thus, resprouting should be considered as an attribute evolved in response to multiple possible selective forces, a sort of reiteration by which a plant reverts to a juvenile state after damage.
Bagging predictors is a method for generating multiple versions of a predictor and using these to get an aggregated predictor. The aggregation averages over the versions when predicting a numerical outcome and does a plurality vote when predicting a class. The multiple versions are formed by making bootstrap replicates of the learning set and using these as new learning sets. Tests on real and simulated data sets using classification and regression trees and subset selection in linear regression show that bagging can give substantial gains in accuracy. The vital element is the instability of the prediction method. If perturbing the learning set can cause significant changes in the predictor constructed, then bagging can improve accuracy.
Macroevolutionary studies of the genus Pinus provide the oldest current evidence of fire as an evolutionary pressure on plants and date back to ca. 125 million years ago (Ma). Microevolutionary studies show that fire traits are variable within and among populations, especially among those subject to different fire regimes. In addition, there is increasing evidence of an inherited genetic basis to variability in fire traits. Added together, pines provide compelling evidence that fire can exert an evolutionary pressure on plants and, thus, shape biodiversity. In addition, evolutionary fire ecology is providing insights to improve the management of pine forests under changing conditions. The lessons learned from pines may guide research on the evolutionary ecology of other taxa.
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In 1976-1977, 284 gaps (canopy-opening sizes 1-1490 m^2) were sampled (age, size, species composition) from old-growth mesic forests in Great Smoky Mountains National Park, Joyce Kilmer Wilderness Area and Walker Cove Research Natural Area. In 1983, the woody vegetation (stems @>1 cm dbh) of 273 of these gaps was resampled, rates of gap closure by canopy tree branch growth and sapling height growth were estimated, and incidences of disturbances occurring since 1976-1977 were noted. The average yearly crown extension growth rate was 18 cm/yr, with much variation among species and individuals. Some individual crowns grew into the canopy opening as much as 4 m in the 7 yr. Saplings grew an average of 30 cm/yr in height, again with much variation. Overall, taller saplings grew somewhat faster than smaller ones and saplings in large gaps grew faster than those in small gaps. These two rates of gap closure together suggest that most saplings will require two or more gap episodes to reach the forest canopy. For woody vegetation, basal area per unit gap area was originally highest in small gaps, though it increased between sampling dates most in large gaps. Stem density had been highest in small old gaps, but decreased the most in old gaps. Tsuga canadensis, Fagus grandifolia, Acer saccharum, and Halesia carolina were the most important species in the gaps studied. Most species did not change in relative density or dominance between the two sampling dates and showed no significant correlations between those parameters and gap size and age. Overall, Tsuga and Fagus decreased and Acer saccharum increased in importance. High rates of repeat disturbance favor species able to grow in intermediate light levels and to survive several periods of suppression before reaching the canopy.
Statistical approaches to overdispersion, correlated errors, shrinkage estimation, and smoothing of regression relationships may be encompassed within the framework of the generalized linear mixed model (GLMM). Given an unobserved vector of random effects, observations are assumed to be conditionally independent with means that depend on the linear predictor through a specified link function and conditional variances that are specified by a variance function, known prior weights and a scale factor. The random effects are assumed to be normally distributed with mean zero and dispersion matrix depending on unknown variance components. For problems involving time series, spatial aggregation and smoothing, the dispersion may be specified in terms of a rank deficient inverse covariance matrix. Approximation of the marginal quasi-likelihood using Laplace's method leads eventually to estimating equations based on penalized quasilikelihood or PQL for the mean parameters and pseudo-likelihood for the variances. Implementation involves repeated calls to normal theory procedures for REML estimation in variance components problems. By means of informal mathematical arguments, simulations and a series of worked examples, we conclude that PQL is of practical value for approximate inference on parameters and realizations of random effects in the hierarchical model. The applications cover overdispersion in binomial proportions of seed germination; longitudinal analysis of attack rates in epilepsy patients; smoothing of birth cohort effects in an age-cohort model of breast cancer incidence; evaluation of curvature of birth cohort effects in a case-control study of childhood cancer and obstetric radiation; spatial aggregation of lip cancer rates in Scottish counties; and the success of salamander matings in a complicated experiment involving crossing of male and female effects. PQL tends to underestimate somewhat the variance components and (in absolute value) fixed effects when applied to clustered binary data, but the situation improves rapidly for binomial observations having denominators greater than one.
There are two broad mechanisms by which plant populations persist under recurrent disturbances: resprouting from surviving tissues, and seedling recruitment. Species can have one of these mechanisms or both. However, a coherent framework explaining the differential evolutionary pressures driving these regeneration mechanisms is lacking. We propose a bottom-up approach in addressing this question that considers the relative survivorship of adults and juveniles in an evolutionary context, based on two assumptions. First, resprouting and seeding can be interpreted by analogy with annual versus perennial life histories; that is, if we consider disturbance cycles to be analogous to annual cycles, then resprouting species are analogous to the perennial life history with iteroparous reproduction, and obligate seeding species that survive disturbances solely through seed banks are analogous to the annual life history with semelparous reproduction. Secondly, changes in the selective regimes differentially modify the survival rates of adults and juveniles and thus the relative costs and benefits of resprouting versus seeding. Our approach provides a framework for understanding temporal and spatial variation in resprouting and seeding under crown-fire regimes. It accounts for patterns of coexistence and environmental changes that contribute to the evolution of seeding from resprouting ancestors.
Aim: Forest ecosystems dominated by fire-sensitive species could suffer shifts in composition under altered crown fire regimes mediated by climate change. The aims of this study were to: (1) study the spatio-temporal patterns and the climatic distribution of fires in Scots pine (Pinus sylvestris) forests during the last 31 years in north-eastern Spain, (2) evaluate the climatic vulnerability to fire of these forests in Spain, (3) analyse the regeneration of Scots pine after fire, and (4) predict the mid-term maintenance or replacement of Scots pine in burned areas. Location: Catalonia (north-eastern Spain): the southern distribution limit of Scots pine. Methods: We characterized the spatio-temporal and the climatic distribution of fires that occurred in Catalonia between 1979 and 2009. We used a generalized linear model to characterize the climatic vulnerability to fire of Scots pine in the whole of Spain. We assessed the regeneration of the species after crown fires in nine burned areas in Catalonia. The resulting data were integrated into a stochastic matrix model to predict the mid-term maintenance or replacement of Scots pine in burned areas. Results: During the last three decades, Scots pine forests distributed in dry sites were most affected by fire. Our assessment of the vulnerability to fire of Scots pine forests in Spain as a whole, based on climatic and topographical variables, showed that 32% of these forests are vulnerable to fire, and that this proportion could increase to 66% under a conservative climate change scenario. Field data showed almost no regeneration of Scots pine after crown fires, and a limited capacity to recolonize from unburned edges, even in relatively old fires, with 90% of recruits located in the first 25 m from the edge. This process could be delayed by the elapsed time for new recruits to achieve reproductive maturity, which we estimated to be c. 15 years. Finally, our matrix model predicted the replacement of burned Scots pine forests by oak (Quercus sp.) forests, shrublands or mixed resprouter forests. Main conclusions: Increased vulnerability to fire of Scots pine forests under future, warmer conditions may result in vegetation shifts at the southern edge of the distribution of the species.
Aim Forest ecosystems dominated by fire‐sensitive species could suffer shifts in composition under altered crown fire regimes mediated by climate change. The aims of this study were to: (1) study the spatio‐temporal patterns and the climatic distribution of fires in Scots pine ( Pinus sylvestris ) forests during the last 31 years in north‐eastern Spain, (2) evaluate the climatic vulnerability to fire of these forests in Spain, (3) analyse the regeneration of Scots pine after fire, and (4) predict the mid‐term maintenance or replacement of Scots pine in burned areas.
Location Catalonia (north‐eastern Spain): the southern distribution limit of Scots pine.
Methods We characterized the spatio‐temporal and the climatic distribution of fires that occurred in Catalonia between 1979 and 2009. We used a generalized linear model to characterize the climatic vulnerability to fire of Scots pine in the whole of Spain. We assessed the regeneration of the species after crown fires in nine burned areas in Catalonia. The resulting data were integrated into a stochastic matrix model to predict the mid‐term maintenance or replacement of Scots pine in burned areas.
Results During the last three decades, Scots pine forests distributed in dry sites were most affected by fire. Our assessment of the vulnerability to fire of Scots pine forests in Spain as a whole, based on climatic and topographical variables, showed that 32% of these forests are vulnerable to fire, and that this proportion could increase to 66% under a conservative climate change scenario. Field data showed almost no regeneration of Scots pine after crown fires, and a limited capacity to recolonize from unburned edges, even in relatively old fires, with 90% of recruits located in the first 25 m from the edge. This process could be delayed by the elapsed time for new recruits to achieve reproductive maturity, which we estimated to be c. 15 years. Finally, our matrix model predicted the replacement of burned Scots pine forests by oak ( Quercus sp.) forests, shrublands or mixed resprouter forests.
Main conclusions Increased vulnerability to fire of Scots pine forests under future, warmer conditions may result in vegetation shifts at the southern edge of the distribution of the species.
Our study aimed to identify and explore the main factors that influence tree recruitment of multiple species at a regional scale across peninsular Spain, an understanding of which is essential for predicting future forest species composition in the face of ongoing environmental change. The study focused on the dynamics of the key transition phase from saplings to adult trees.
The forests of peninsular Spain.
We used the extensive network of plots sampled in two consecutive Spanish national forest inventories (> 30,000 plots) to identify the factors that determine regeneration patterns of the 10 most abundant forest species of Spain at relatively large temporal (c. 10 years) and spatial scales (across Spain): five coniferous species of Pinus (pines) and five broadleaved species of the genera Fagus and Quercus. We fitted separate generalized linear models for the pine species and the broadleaved species to assess the response of sapling abundance and ingrowth rate to the spatial variability of climate (temperature, water availability and recent warming), forest structure (tree density, understorey and overstorey canopy cover, and basal area change) and disturbances (previous forest logging, wildfires and grazing).
Mean sapling abundance was four times higher for broadleaved species than for pines, while mean annual ingrowth was twice as high. Sapling abundance and ingrowth rate were mainly determined by stand structure, both in pines and broadleaved trees. The direct effects of disturbances and climate were comparatively smaller, and there was no detectable effect of recent warming.
The higher values of ingrowth rate of broadleaved species can be explained by their ability to maintain a higher sapling bank due to their greater shade tolerance. This differential response of pines and broadleaved species to canopy closure suggests a probable increase in broadleaved species at the expense of pines. This transition could occur earlier in stands with faster canopy closure dynamics. Spatially explicit, mixed-species demographic models incorporating both the ingrowth and the tree mortality components are needed for predicting the composition of future forests.
In this chapter, we show that Mediterranean forests can be considered complex adaptive systems and thus be understood and managed according to the principles of complexity science. First, we examine the profound impact of the long history of human use on Mediterranean forest ecosystems and how this human impact has created a unique set of conditions not commonly found elsewhere in the world.
Then we define management strategies that increase the resilience and adaptive capacity of Mediterranean forests facing rapidly changing conditions.
Regeneration of non fire-adapted conifers following crown fires on the European Alps is often delayed or unsuccessful. Fire may limit establishment by eliminating seed trees, altering soil properties, or modifying microsite and soil conditions via disturbance legacies. However, the effect of soil legacies on post-fire establishment has rarely been discussed. We analyzed the abundance of Scots pine regeneration in a 257ha wildfire in an inner-alpine forest. Our aims were (1) to model fire intensity at the soil surface and topsoil heating along a gradient of increasing fire severities; (2) to assess the differences in soil properties along the fire severity gradient; (3) to model the effect of disturbance and soil legacies on the density of pine seedlings. We reconstructed fire behavior and soil heating with the First Order Fire Effects Model (FOFEM), tested the effect of fire severity on soils by nonparametric distributional tests, and modeled seedling density as a function of site, disturbance and soil legacies by fitting a GLM following a variable selection procedure. Topsoil heating differed markedly between the moderate and high severity fires, reaching temperatures high enough to strongly and permanently alter soil properties only in the latter. High fire severity resulted in decreased soil consistency and wet aggregate stability. Burned soils had lower organic matter and cations than those unburned. Pine seedlings favored low-fertility, eroded, and chemically poor sites. Establishment was facilitated by the presence of coarse woody debris, but hampered by increasing distance from the seed source. These results suggest that in dry, inner-alpine valleys, fire residuals and soil legacies interact in determining the success of Scots pine re-establishment. High severity fire can promote favorable soil conditions, but distance from the seed source and high evaporation rates of bare soils must be mitigated in order to ensure a successful restoration.
Random forests are a combination of tree predictors such that each tree depends on the values of a random vector sampled independently and with the same distribution for all trees in the forest. The generalization error for forests converges a.s. to a limit as the number of trees in the forest becomes large. The generalization error of a forest of tree classifiers depends on the strength of the individual trees in the forest and the correlation between them. Using a random selection of features to split each node yields error rates that compare favorably to Adaboost (Y. Freund & R. Schapire, Machine Learning: Proceedings of the Thirteenth International conference, ***, 148–156), but are more robust with respect to noise. Internal estimates monitor error, strength, and correlation and these are used to show the response to increasing the number of features used in the splitting. Internal estimates are also used to measure variable importance. These ideas are also applicable to regression.
Summary
1. Tree recruitment in Mediterranean ecosystems is strongly limited at the seedling stage by drought. Increasing evidence shows the critical positive role of the canopy nurse effect on seedling survival which results from direct and indirect, positive and negative, interactions between species.
2. Most studies, however, have only focused on the effects of tree canopy on water and light, ignoring other critical factors affecting seedling regeneration, such as canopy effects on high temperatures and the competing herb biomass.
3. Here, we evaluate how tree canopy cover and removal of herbs affect the survival and growth of seedlings of two dominant Mediterranean Quercus species during a three-year study. We use an integrated model that combines several data sets to quantify and predict regeneration dynamics along environmental gradients of soil moisture, temperature and light.
4. Low soil moisture, increased soil temperature and herb biomass negatively affected seedling survival of both Quercus species. Seedling growth was positively associated with increasing soil moisture and light.
5. Although tree canopy cover directly facilitated seedling survival in both Quercus species, it also negatively affected herb biomass and thus indirectly facilitated the survival of Q. suber, but not of Q. ilex seedlings at low levels of soil moisture.
6. Overall, tree canopies increased seedling survival but not growth during the establishment phase, mainly by ameliorating the effects of low soil moisture and high temperatures. Tree canopy indirectly facilitated survival of Quercus suber seedlings by negatively affecting the competing herb layer.
7. Synthesis and applications. To improve tree recruitment and conserve Mediterranean Quercus woodlands, the removal of herbs should be integrated into management plans for dry habitats. Interactions between abiotic and biotic factors may also effect the regeneration of these tree species. In particular, a healthy tree canopy will become important for providing conditions to facilitate seedling establishment if these habitats become drier and warmer, as predicted by some climate change scenarios.
Aim There is increasing concern regarding sustainable management and restoration of planted forests, particularly in the Mediterranean Basin where pine species have been widely used. The aim of this study was to analyse the environmental and structural characteristics of Mediterranean planted pine forests in relation to natural pine forests. Specifically, we assessed recruitment and woody species richness along climatic, structural and perturbation gradients to aid in developing restoration guidelines.
Location Continental Spain.
Methods We conducted a multivariate comparison of ecological characteristics in planted and natural stands of main Iberian native pine species ( Pinus halepensis , Pinus pinea , Pinus pinaster , Pinus nigra and Pinus sylvestris ). We fitted species‐specific statistical models of recruitment and woody species richness and analysed the response of natural and planted stands along ecological gradients.
Results Planted pine forests occurred on average on poorer soils and experienced higher anthropic disturbance rates (fire frequency and anthropic mortality) than natural pine forests. Planted pine forests had lower regeneration and diversity levels than natural pine forests, and these differences were more pronounced in mountain pine stands. The largest differences in recruitment – chiefly oak seedling abundance – and species richness between planted and natural stands occurred at low‐medium values of annual precipitation, stand tree density, distance to Quercus forests and fire frequency, whereas differences usually disappeared in the upper part of the gradients.
Main conclusions Structural characteristics and patterns of recruitment and species richness differ in pine planted forests compared to natural pine ecosystems in the Mediterranean, especially for mountain pines. However, management options exist that would reduce differences between these forest types, where restoration towards more natural conditions is feasible. To increase recruitment and diversity, vertical and horizontal heterogeneity could be promoted by thinning in high‐density and homogeneous stands, while enrichment planting would be desirable in mesic and medium‐density planted forests.
A precise knowledge of forest demographic gradients in the Mediterranean area is essential to assess future impacts of climate change and extreme drought events. Here we studied the geographical patterns of forest demography variables (tree recruitment, growth and mortality) of the main species in Spain and assessed their multiple ecological drivers (climate, topography, soil, forest stand attributes and tree-specific traits) as well as the geographical variability of their effects and interactions. Quantile modeling analyses allowed a synthetic description of the gradients of multiple covariates influencing forest demography in this area. These multivariate effect gradients showed significantly stronger interactions at the extremes of the rainfall gradient. Remarkably, in all demographic variables, qualitatively different levels of effects and interactions were observed across tree-size classes. In addition, significant differences in demographic responses and effect gradients were also evident between the dominant genus Quercus and Pinus. Quercus species presented significantly higher percentage of plots colonized by new recruits, whereas in Pinus recruitment limitation was significantly higher. Contrasting positive and negative growth responses to temperature were also observed in Quercus and Pinus, respectively. Overall, our results synthesize forest demographic responses across climatic gradients in Spain, and unveil the interactions between driving factors operating in the drier and wetter edges.
We carried out a systematic review and meta-analysis of the effects of forest thinning and burning treatments on restoring fire behavior attributes in western USA pine forests. Ponderosa pine (Pinus ponderosa) and Jeffrey pine (Pinus jeffreyi), with co-occurring species, are adapted to a disturbance regime of frequent surface fires, but extended fire exclusion and other factors have led to historically uncharacteristically dense stands and high fuel loadings, supporting high-severity fires. Treatments to begin to reverse these changes and reduce fuel hazards have been tested experimentally and observations of wildfire behavior in treated stands have also been reported. Using a systematic review methodology, we found 54 studies with quantitative data suitable for meta-analysis. Combined treatments (thinning + burning) tended to have the greatest effect on reducing surface fuels and stand density, and raising modeled crowning and torching indices, as compared to burning or thinning alone. However, changes in canopy base height and canopy bulk density were not consistently related to treatment intensity, as measured by basal area reduction. There are a number of qualifications to the findings. First, because it is not feasible to subject treated areas to severe fire experimentally, inferences about potential fire behavior rely on imperfect modeling techniques. Second, research has not been carried uniformly over the ranges of the pine forests, although we found no significant differences in treatment effects between regions or forest types. Overall, however, meta-analysis of the literature to date strongly indicates that thinning and/or burning treatments do have effects consistent with the restoration of low-severity fire behavior.
Plant colonization studies usually address density-dependent processes in the narrow sense of recruitment constraints due to negative density-dependent seed and seedling mortality. However, complex density-dependent effects may be involved in additional stages of the recruitment process. We hypothesized that seed arrival and seedling establishment are influenced by density dependence acting at small scales at the site of colonization, and at larger scales as a function of the colonizing species' landscape abundance. These hypotheses were tested in a study of colonization of pine forests by oaks in a heterogeneous Mediterranean landscape. Maximum-likelihood models show that density effects switch from positive to negative along the range of landscape-scale oak seed source abundance. Contrary to expectations, high seed source densities limited oak recruitment, suggesting a landscape-scale Janzen-Connell effect. We propose a range of mechanisms that generate positive or negative density dependence during colonization, resulting in nonlinear density-dependent feedbacks that can generate unexpected colonization patterns.
ABSTRACT
Aim: Large-scale patterns of limitations in tree recruitment remain poorly described in the Mediterranean Basin, and this information is required to assess the impacts of global warming on forests. Here we unveil the existence of opposite trends of recruitment limitation between the dominant genera Quercus and Pinus on a large scale and identify the key ecological drivers of these diverging trends.
Location: Spain.
Methods: We gathered data from the Spanish National Forest inventory to assess recruitment trends for the dominant species (Pinus halepensis, P. pinea, P. pinaster, P. nigra, P. sylvestris, P. uncinata, Quercus suber, Q. ilex, Q. petraea, Q. robur, Q. faginea and Q. pyrenaica). We assessed the direct and indirect drivers of recruitment by applying Bayesian structural equation modeling techniques.
Results: Severe limitations in recruitment were observed across extensive areas in all Pinus species studied, with recruitment failure affecting 54-71% of the surveyed plots. In striking contrast, Quercus species expanded into 41% of the plots surveyed versus only 10% for Pinus and had a lower local recruitment failure (29% of Quercus localities compared to 63% for Pinus species). Bayesian structural equation models highlighted the key role of the presence of Q. ilex saplings and the increase in the basal area of Q. ilex in limiting Pinus recruitment in five Pinus species. The recruitment of P. sylvestris and P. nigra showed the most negative trends and was negatively associated with the impacts of fire.
Main conclusions: This study identified Q. ilex, the most widespread species in this area, as a key driver of recruitment shifts on a large scale, negatively affecting most pine species with the advance of forest succession. These results highlight that the future expansion/contraction of Q. ilex stands with ongoing climate change will be a key process indirectly controlling the demographic responses of Pinus species in the Mediterranean Basin.
It is widely accepted that the postfire recovery in Mediterranean plant com- munities is carried out by direct regeneration, i.e., the fast recovery of a plant community with the same species pool that it had immediately prior to disturbance. However, there is evidence that not all plant species in the Mediterranean basin survive fire in all situations, suggesting that the direct regeneration process might not apply to all situations. We analyze whether the main combinations of forest tree species (up to 16) of the western Mediterranean basin exhibit a postfire direct regeneration process. Based on data from field surveys, we have developed a stochastic model to predict the medium-term forest dynamics. In general, Quercus species (resprouters) and the pines Pinus halepensis and P. pinaster (seeders that produce abundant seedlings) showed direct regeneration patterns. In contrast, forests of P. nigra, P. sylvestris, and P. pinea (seeders that produce few seedlings) changed to other situations after fire. This outcome was validated by additional data from plots with known fire history. These results did not support completely the direct regeneration model, since only half of the combinations of tree species analyzed exhibited a .50% probability of recovering the original prefire situation after fire. This partial failure of direct regeneration evidences the need for reconsidering restoration and conservation plans for Mediterranean ecosystems after fire.
Changes in climate may reduce the success of natural regeneration and hence require adjustments to silvicultural practices. Special attention is required for species such as Spanish black pine (Pinus nigra Arn. ssp salzmannii) because of impediments to achieve successful natural regeneration. Spanish black pine seed germination was studied under field conditions at a normal altitude for the species and at the upper altitude limit of its distribution in the Cuenca Mountains (southeastern Spain). The aim was to assess the effect of location, overstory density, soil treatment, sowing date and climatic characteristics on regeneration success. ANOVA results indicated a significant interaction of location by overstory density on germination rates. A logistic model containing the temperature variable TemminAc, the light radiation effect (Rad variable) and the interaction term between soil treatment (Soil Treat) and radiation (Soil Treat×Rad) correctly predicted the germination success in 94% of cases. Moreover, two Poisson regression models (one for each experimental site) showed that the number of germinated seeds depends on stand basal area (G), soil treatment (Soil Treat) and sowing date (Seed Season). Conservation management could increase initial seedling recruitment by promoting soil preparation and higher basal area levels. The populations at higher altitudes are particularly endangered due to the unfavourable environmental conditions for the development of this species, which seriously affect seed rain density and germination rates.
A two-level multifactor experimental approach was used to compare seed germination and seedling performance of two Mediterranean tree species: the early successional Aleppo pine (Pinus halepensis Mill.) and the late successional holm oak (Quercus ilex L.). In a first experiment germination rate was evaluated under the combined effects of shade, nitrogen availability, and pine or holm oak leaf litter. In a second experiment we tested for the effects of shade, nutrient availability, and litter type on seedling survival, growth and biomass allocation. Holm oak showed higher germination rates under shaded than under unshaded conditions, while Aleppo pine showed no differences between shaded and unshaded conditions. Nitrogen availability and litter type had no significant effect on germination of either species. Both species showed increased RGR, but also higher mortality rates, when grown in an enriched nutrient environment. While Aleppo pine showed no differences in RGR and mortality rate under different shading levels, RGR decreased and mortality increased for holm oak in full light. Increased radiation decreased LAR, SLA and height:diameter ratio, and increased RWR and R/S in both species, although Aleppo pine showed more pronounced changes. Unlike Aleppo pine, holm oak responded to increased nutrient availability by decreasing R/S and increasing LAR. From these results, no seed-seedling conflicts were found in either species, but a trade-off does seem to exist for holm oak between biomass allocation traits deployed in response to increased nutrient availability and radiation. Aleppo pine outperformed holm oak under most environmental conditions tested and showed a wider regeneration niche.