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Diversifying sub-Mediterranean pinewoods with oak species in a context of assisted migration: Responses to local climate and light environment
Abstract
Questions
How do thermal migration distance and extreme cold events affect seedling emergence and survival in assisted migration schemes in the sub‐Mediterranean context? What role does plant provenance play? Can biotic interactions such as nurse effect of the overstorey and shrub layer buffer the negative responses to plant translocation? Are any of these effects species‐specific?
Location
Three pinewoods in the Catalan Pre‐Pyrenees, northeast Iberian Peninsula.
Methods
We used a replicated field trial to test the early years establishment of two contrasted provenances of four Quercus species ( Q. coccifera , Q. ilex , Q. faginea and Q. pubescens ) that were sown and planted along gradients of elevation and understorey microsite conditions in sub‐Mediterranean pinewoods. Seedling responses to translocation were evaluated through seedling emergence, seedling survival and re‐sprouting after dieback events according to seedling provenance, thermal migration distance, extreme cold events and microenvironment.
Results
The study reports high success of both the planting (with an overall 76.3% of initial 3‐yr survival) and sowing (with an overall 50% of seedling emergence) experiments. The results show that: (1) the thermal migration distance and the occurrence of extreme cold events have strong effects on the responses of the translocated species (particularly the evergreen oaks); (2) the forest overstorey plays an important role in attenuating the negative effects of thermal migration distance on seedling survival; and (3) these responses are species‐specific. The evergreen Quercus species showed more evidence of high ecotypic differentiation in terms of cold tolerance, enabling local provenances to respond better to translocation. In contrast, marcescent species, showed high phenotypic plasticity that led to a better overall establishment success.
Conclusion
The implementation of assisted migration is a feasible option to increase the diversity and resilience of the sub‐Mediterranean pinewoods. Assisted migration programmes should manage risks by thoroughly considering thermal migration distances and the occurrence of extreme cold events when selecting species and seed sources, since Mediterranean tree species show different strategies regarding adaptation to cold. Programme managers should also consider the advantage of planting/sowing under relatively closed canopy to buffer some of the negative responses associated with translocation.
... By choosing to focus on a critical life history stage for trees, the regeneration niche, they provide results that are highly useful and informative to vegetation scientists interested in learning more from provenance experiments that consider climate change adaptation strategies. Martin-Alcόn et al. (2016) found high survival across most of their trials and strong correlates of extreme cold events to explain failure. They conclude by recommending managing risk of planting failure through consideration of 'thermal migration distance', focusing on extreme weather events, rather than mean temperature and precipitation envelopes. ...
... A third, and critical vector of risk that remains unaddressed in the work of Martin-Alcόn et al. (2016) is that of social acceptance. Early work in assisted migration has highlighted the outcome that society may or may not accept an assisted migration action as a socially acceptable management solution to a conservation challenge (Schwartz et al. 2012). ...
... If prevailing opinion on the impact of climate change on biodiversity is correct (Javeline et al. 2015), then society faces tragic choices, balancing extinction risk reduction against the risk of creating an invasive species problem and the certainty of reducing our sense of the natural. Getting out ahead of the issue through maturing our biological understanding through carefully controlled experiments such as those described by Martin-Alcόn et al. (2016) is critical. Fig. 1. ...
Assisted colonization is a proposed climate change adaptation strategy. Martin-Alcοn et al. (Applied Vegetation Science, this issue) report an experiment to evaluate the efficacy of assisted colonization and identify thermal distance as a critical consideration. By extension, we should consider the role that ecological distance and socio-political distance play within any plan to reduce extinction risk through assisted colonization.
... Early in the growing season, the rapid recovery of the systems with increased φP0 and PIabs values towards the evening and higher values during the night (Fig. 1S) speaks for a dynamic protection process. This could be achieved either by dynamic photoinhibition including resynthesis of the D1 protein (Krause et al. 1995) or by a temporary downregulation mechanism of PSII like an increase in dissipation of excitation energy as heat (Epron et al. 1992, Long et al. 1994. Brüggemann et al. (2009) also found dynamic photoinhibition during the day in different oak species indicating that the light-harvesting capacity exceeded both, the capacity to utilize energy through photosynthesis and the ability of heat dissipation. ...
... These differential regimes affected PSII efficiency and resulted in lower chlorophyll a fluorescence values in the southern vs. the northern common garden ( Fig. 2A,D), attributed to an efficient strategy for light acclimation Demmig-Adams 2004, Pollastrini et al. 2016) in the former and the favorable effect of partial shading (Flores and Jurado 2003, Valladares et al. 2008, Caldeira et al. 2014, Martín-Alcón et al. 2016) which reduces leaf temperatures, water evaporative demand, and photoinhibition in the latter. By disassembling the predawn values of PI abs into its components, not only φP0 but also RC/ABS and ψE0 were enhanced (Fig. 1S) in the SWA common garden, consistent with the results of Bantis et al. (2020). ...
Keywords: assisted migration; chlorophyll fluorescence; diurnal variation; gas exchange; Quercus frainetto; Quercus pubescens. Abbreviations: DOY-day of the year; gs-stomatal conductance; OLY-Olympiada/Greece; PIabs-performance index on absorption basis; PNmax-light-saturated net photosynthetic rate; RC/ABS-active reaction centers on absorption base; SWA-Schwanheim/ Germany; WUE-water-use efficiency; φP0-Fv/Fm-maximum quantum efficiency of the reduction of QA; ψE0-the probability that an absorbed photon leads to a reduction further than QA. Oaks may contribute to the stabilization of European forests under climate change. We utilized two common gardens established in contrasting growth regimes, in Greece (Olympiada) and Germany (Schwanheim), to compare the diurnal photosynthetic performance of a Greek and an Italian provenance of two Mediterranean oaks (Quercus pubescens and Q. frainetto) during the 2019 growing season. Although the higher radiation in the southern common garden led to a strong midday depression of chlorophyll a fluorescence parameters (maximum quantum efficiency of PSII, performance index on absorption basis), comparable light-saturated net photosynthetic rates were achieved in both study areas. Moreover, both species and provenances exhibited analogous responses. Q. pubescens had enhanced chlorophyll a fluorescence traits but similar photosynthetic rates compared to Q. frainetto, whereas the provenances did not differ. These findings indicate the high photosynthetic efficiency of both oaks under the current climate in Central Europe and their suitability for assisted migration schemes. Highlights • High radiation led to strong photoinhibition of both oaks at the southern site • At both sites, only small differences were observed between species and provenances • Both oak species show high potential for assisted migration to Central Europe
... One of the most important practices to increase species richness is the choice of regeneration cut or the silvicultural system, respectively. Here, the future species composition of the forest can actively be changed by replacing tree species and/or tree individuals sensitive to climate change with trees of native or introduced species and/or species' provenances that are potentially better adapted to future climate conditions (called active adaptation; Martín-Alcón et al. 2016;Bolte et al. 2009). Examples for this strategy are the ongoing conversion of pure Norway spruce stands into mixed stands or silvicultural measures aiming at replacing species such as Norway spruce by other species of comparable economic value (e.g., Douglas fir). ...
... Climate change will cause many tree species to lose a part of their current habitat but will also enable them to colonize new habitats (e.g., del Río et al. 2018). As natural migration is often slow, forest managers are examining the option of assisted migration (Martín-Alcón et al. 2016;Gömöry et al. 2020). A main premise of SFM is that silviculture based on patterns and processes found in old-growth forests will maintain the provision of important habitats for biodiversity (Schütz et al. 2016). ...
Mountain forests in Europe have to face recently speeding-up phenomena related to climate change, reflected not only by the increases in the mean global temperature but also by frequent extreme events, that can cause a lot of various damages threatening forest stability. The crucial task of management is to adapt forests to environmental uncertainties using various strategies that should be undertaken to enhance forest resistance and resilience, as well as to maintain forest biodiversity and provision of ecosystem services at requested levels. Forests can play an important role in the mitigation of climate change. The stand features that increase forest climate smartness could be improved by applying appropriate silvicultural measures, which are powerful tools to modify forests. The chapter provides information on the importance of selected stand features in the face of climate change and silvicultural prescriptions on stand level focusing to achieve the required level of climate smartness. The selection of silvicultural prescriptions should be also supported by the application of simulation models. The sets of the various treatments and management alternatives should be an inherent part of adaptive forest management that is a leading approach in changing environmental conditions.
... D'autres études mettent en avant une augmentation de la mortalité de plantules de chêne avec la lumière (Matías et al. 2011, Pérez-Ramos et al. 2013a, Martín-Alcón et al. 2016, contrairement à ce qui est observé à St Mitre. Or, Matías et al. (2011) étudient un site où l'humidité du sol est plus forte en forêt qu'en découvert. ...
... Les éclaircies trop fortes -ou les coupes rases -peuvent par contre laisser craindre un risque de mortalité plus fort par dessication (Matías et al. 2011, Martín-Alcón et al. 2016) ou un blocage de la croissance des espèces décidues par photoinhibition (chapitre 1). À Barbentane, les plantules de chêne ont eu des taux de survie très bas sous un couvert de pin d'Alep de 10m 2 /ha. ...
Installation d’espèces feuillues en forêt de pin d’Alep : interactions avec les strates arborées et arbustives. L’installation de plantules est une phase critique fortement influencée par les interactions avec la végétation établie - compétition ou facilitation. Dans cette thèse, nous montrons que l’effet du pin d’Alep ou d'arbustes sur l’installation d’espèces feuillues dépend de la densité du couvert, de la stratégie des espèces cibles et nurses et des conditions locales. Sous couverts très denses, la survie et la croissance des plantules sont drastiquement limitées par compétition lumineuse et hydrique, le stress hydrique des plantules étant renforcé par une faible allocation de biomasse vers les racines. À l’autre extrémité du gradient, en milieu ouvert, la photoinhibition et la concurrence avec les herbacées peuvent limiter l'installation des plantules. Les espèces sclérophylles sempervirentes sont peu sensibles aux fortes irradiances, températures et demandes évaporatives et peuvent profiter de conditions favorables momentanées par polycyclisme. L’effet d’un couvert végétal sur ces espèces est donc principalement compétitif, tandis que les espèces décidues à fort SLA bénéficient d’un couvert modéré qui tamponne les extrêmes. En pépinière, la litière des principales espèces ligneuses modifie les propriétés physico-chimiques et microbiologiques du sol sous-jacent mais sans effet sur des plantules de chêne au bout de 2 ans, montrant un faible effet allélopathique. L’éclaircie des peuplements de pin d’Alep denses est une stratégie pour faciliter l’installation d’espèces feuillues et ainsi améliorer la diversité et la résilience au feu des forêts. L’optimum de couvert semble se déplacer vers des couverts plus denses dans des sites à conditions climatiques ou édaphiques plus sévères et pour les espèces décidues.
... The initial adaptation of the non-native species to their new habitat seemed thus best on the OLD experimental site, which has the smallest climatic distance to the area of origin of the seed sources. Similarly, testing early establishment of four Quercus species, Martín-Alcón et al. (2016) found lower summer mortality in the provenances which came from drier sites, possibly due to their more conservative water-use behaviour. The highest late mortality, but also the highest survival rate of the native relative to the nonnative species, were recorded in BRU (Table 4). ...
... The survival of these shade-tolerant tree species generally improved with time, but H lat still remained high relative to the native species three to 4 years after planting. One explanation for the continuing seedling mortality of these shade-tolerant tree species might be the complete lack of a forest overstory, which can play an essential role during the establishment phase as it protects seedlings from direct exposure to light and thus reduces their evaporative demand (Martín-Alcón et al. 2016). In support of this, Tabari et al. (2005) reported higher survival rates of F. orientalis seedlings from northern Iran in small gaps (50 m 2 ) than in larger gaps (600 m 2 ) with more light intensity. ...
Climate projections indicate large increases in temperature, requiring tree species to adapt or migrate faster than observed historic rates. In Central Europe, discussion in forest management has increasingly focused on how humans can assist these adaptation/migration processes, especially when important forest ecosystem services are at risk. One option is to introduce non-native tree species to help forest ecosystems adapt to climate change. We established a long-term experiment in autumn 2012 on five study sites in climatically different regions of Central Europe. The performance of five non-native tree species from warmer climates (Abies bornmuelleriana Mattf., Cedrus libani A. Rich., Fagus orientalis Lipsky, Tilia tomentosa Moench and Tsuga heterophylla Sarg.) was compared to that of one local species native to each site. We monitored sapling survival during the first 4 years after planting. Small differences in timing of inventory campaigns were overcome by fitting a Weibull function to survival curves and analysing time-harmonized estimates for equal biannual periods. Sapling mortality decreased over time, but early after planting, it differed between species. The native and the two non-native broadleaved species showed higher survival than the non-native coniferous species. Moreover, the site conditions of the open areas seemed to initially hamper the growth of shade-tolerant species. All species performed reasonably well during the relatively short observation period. Any differences between hazard rates almost vanished 4 years after planting, which suggests that all species tested are likely to thrive under current climate conditions. Long-term observations are, however, needed to corroborate these results.
... La elección del gradiente de elevación se basó en el gradiente observado del promedio anual de las temperaturas mínimas diarias (Tmin), considerando que este es uno de los atributos climáticos que más pueden condicionar la adaptación de las especies en actuaciones de migración asistida. De esta manera, se eligió el nivel altitudinal superior con el objetivo de superar ligeramente el rango de Tmin observado a lo largo del área de distribución actual de la procedencia local de las 3 especies, y el nivel altitudinal inferior para que se encontrara dentro pero aún en el extremo inferior del rango de Tmin observado a lo largo de la actual área de distribución de las procedencias termófilas (MARTÍN-ALCÓN, et al. 2016). En cada elevación de cada monte se establecieron dos parcelas de 12 x 12 metros: una de las parcelas se ubicó bajo dosel continuo de pinar y la otra se colocó bajo un pequeño hueco del dosel, con el fin de abarcar un gradiente de condiciones lumínicas y de protección del arbolado. ...
... Las tres especies pueden encontrarse creciendo naturalmente en la zona de estudio, no tanto en forma de bosques puros de frondosas, sino más frecuentemente en forma de individuos dispersos o pequeños grupos, siendo algunas de las principales especies protagonistas de la progresiva diversificación espontánea de estos pinares (MARTÍN-ALCÓN, et al. 2015, NAVARRO-GONZÁLEZ, et al. 2013, VAYREDA, et al. 2013. Las tres especies pueden clasificarse en relación a su tolerancia a la sequía como Qi> Qf> Qp, y en el orden opuesto en relación a su tolerancia al frío (MARTÍN-ALCÓN, et al. 2016). Todas ellas pueden ser definidas como poco tolerantes, o de tolerancia intermedia a la sombra (NIINEMETS y VALLADARES 2006), aunque se ven favorecidas por el sombreado moderado a alto durante la fase de establecimiento de las plántulas (GÓMEZ-APARICIO, et al. 2008. ...
... Surprisingly, none of the decision rules proposed the intuitive solution of translocating from the south to northern locations in any of the target zones. This can be explained by the fact that southern populations present generally lower height potential than northern ones (our example is supporting this hypothesis, showing that the Northwest provenance was almost always the preferable option) and it is in line with the potential downsides of planting trees from southern provenances because of the risks of extreme frost events in these southern populations as have already occurred for some translocations (Benito-Garzón et al. 2013a;Benito-Garzón et al. 2013b;Martín-Alcón et al. 2016;Bucharova et al. 2016;Montwé et al. 2016). For instance, populations from the south of the range of Pinus contorta in North America and four perennial plants in Germany did not perform better than the local populations under extreme heat events (Bucharova et al. 2016;Montwé et al. 2016). ...
... Likewise, Pinus pinaster populations from southern Europe planted in northern locations suffered from high mortality after a frost event, whereas the mortality was lower for the local provenances (Benito- Garzón et al. 2013a). Other Mediterranean trees such as Quercus coccifera, Q. ilex, Q. faginea and Q. pubescens showed similar sensitivity to extreme cold events in recent translocations (Martín-Alcón et al. 2016). These examples show that moving populations from the south to the north is more complex than what is intuitively thought and it was not detected as a good choice by our decision framework based on the decision rules, probably because climate change brings non-analog climates that are probably too differentiated in north-south gradients and less differentiated between colder and warmer areas at similar latitudes (Benito- Garzón et al. 2014). ...
The adaptation of social-ecological systems such as managed forests depends largely on decisions taken by forest managers who must choose among a wide range of possible futures to spread risks. We used robust decision theory to guide management decisions on the translocation of tree populations to compensate for climate change. We calibrated machine learning correlational models using tree height data collected from five common garden tests in France where Abies alba provenances from 11 European countries are planted. Resulting models were used to simulate tree height in the planting sites under current and 2050 climates (regional concentration pathway scenarios (RCPs) 2.6, 4.5, 6.0 and 8.5). Our results suggest an overall increase in tree height by 2050, but with large variation among the predictions depending on the provenance and the RCPs. We applied maximin, maximax and minimax decision rules to address outcomes under five uncertain states of the world represented by the four RCPs and the present climate (baseline). The maximin rule indicated that for 2050, the best translocation option for maximising tree height would be the use of provenances from Northwest France into all target zones. The maximax and minimax regret rules pointed out the same result for all target zones except for the ‘Les Chauvets’ trial, where the East provenance was selected. Our results show that decision theory can help management by reducing the number of options if most decision rules converge. Interestingly, the commonly suggested recommendation of using multiple provenances to mitigate long-term maladaptation risks or from ‘pre-adapted’ populations from the south was not supported by our approach.
... For some species, studies have found that seeding or planting trees from source locations that are several degrees Celsius warmer than the translocation site may mitigate the negative impacts of climate change on tree growth and survival (Martin-Alcon et al. 2016, Carbajal-Navarro et al. 2019, Frischbier et al. 2019, Saenz-Romero et al. 2021. Gustafson et al. (2023) showed that under slight changes in climate, assisted migration may indeed increase biomass production through longer growing seasons and CO 2 fertilization. ...
Assisted tree migration has been proposed as a conceptual solution to mitigate lags in biotic responses to anthropogenic climate change. The rationale behind this concept is that tree species currently growing under warmer and drier climates will be more resistant and resilient to the new climatic conditions than tree species naturally growing in currently wetter and colder climates. However, we hypothesize that, by being more stress-tolerant to warmer and drier conditions, translocated species should exhibit different functional attributes, which could induce important ecological and societal costs and overcome the desired benefits of maintaining wood production and other ecosystem services. We used principal component analysis (PCA) to analyze variation in seven traits of 106 tree and tall shrub species from contrasting latitudinal distributions in western North America and Europe to predict the potential functional changes of forest ecosystems due to the translocation of tree species from low to high latitudes. We show that species from both continents differed primarily by their position on the leaf economy spectrum (LES) and their size traits. Even though, in Europe, differences in LES were significantly correlated to species southern latitudinal positions, in both continents differences in size traits were significantly correlated to latitude. These results suggest that assisted migration by translocating more conservative species of shorter stature in currently cooler climates should decrease the buffering capacity of forest canopies, decrease facilitation for understory species, and increase wildfire risks, whose effects have the potential to accelerate climate warming through negative atmospheric feedback processes. As an alternative solution to assisted migration that may accelerate rather than mitigate climate change, we recommend that foresters gradually diversify the vertical structure and layering of the existing forest canopy to maintain a sustainable water cycle and energy balance between the soil, the tree and the atmosphere without increasing the wildfire risk.
... Twardek et al. Biological Conservation xxx (xxxx) 109932 many more assisted migrations have occurred experimentally (e.g., Evans et al., 2016;Martín-Alcón et al., 2016) and many translocations have happened inadvertently that allow researchers to gain insights into assisted migration (e.g., St. Clair et al., 2020;Steiner et al., 2021). Although we did not quantify or validate the outcomes of this conservation tactic, as this was a mapping exercise only, overall, the outcomes of assisted migration on target species were generally considered positive by study authors. ...
Assisted migration entails the human assisted movement of individuals to more climatically-suitable areas within or outside of their current species range to help species respond to climate change. To better understand the potential for assisted migration to benefit species threatened by climate change, we conducted an evidence synthesis to map examples where assisted migration has been implemented around the world. With this mapping exercise, we collate and describe the quantity and key characteristics of the available evidence base, including the taxa, species conservation status, locations, and contexts relating to the use of this conservation tactic. Findings from this exercise highlight that assisted migration has been implemented very few times as a conservation tactic, though assisted migration has been conducted experimentally (for research purposes) and inadvertently (e.g., for reforestation) much more frequently. Assisted migration was most common for plants (particularly trees), followed by birds, and was rarely implemented for other taxa. Our review highlights the need for more research on assisted migration, with particular emphasis on understanding the population- and community-level outcomes of these actions. Our discussion focuses on the potential for assisted migration of Canadian species but will be informative to those considering assisted migration in other jurisdictions.
... Assisting the introduction of genetic material from populations that are already adapted to probable future climate and fire conditions may help a subset of a site's current suite of species to persist longer into the future [239][240][241]. Where there is uncertainty in future climate and fire regimes, diversifying the sources of plant materials to include a range of possible future conditions may help hedge bets [242,243]. This approach may require expanding the acceptable geographic range of plant materials used in revegetation [244]. ...
As the effects of climate change accumulate and intensify, resource managers juggle existing goals and new mandates to operationalize adaptation. Fire managers contend with the direct effects of climate change on resources in addition to climate-induced disruptions to fire regimes and subsequent ecosystem effects. In systems stressed by warming and drying, increased fire activity amplifies the pace of change and scale of severe disturbance events, heightening the urgency for management action. Fire managers are asked to integrate information on climate impacts with their professional expertise to determine how to achieve management objectives in a changing climate with altered fire regimes. This is a difficult task, and managers need support as they incorporate climate adaptation into planning and operations. We present a list of adaptation strategies and approaches specific to fire and climate based on co-produced knowledge from a science–management partnership and pilot-tested in a two-day workshop with natural resource managers and regional stakeholders. This “menu” is a flexible and useful tool for fire managers who need to connect the dots between fire ecology, climate science, adaptation intent, and management implementation. It was created and tested as part of an adaptation framework used widely across the United States and should be applicable and useful in many fire-prone forest ecosystems.
... The availability of tools turning into practice the principle of theoretical decision frameworks available in the literature (Abeli et al., 2014;Hoegh-Guldberg et al., 2008;Schwartz et al., 2012) and the increasing reliability of SDMs will likely boost the applicability of this type of actions and drive experimental trials (e.g. Martín-Alcón et al., 2016). Setting AC goals to aim at is important for planning effective actions in the long term and evaluate feasibility. ...
Effects of climate change are particularly important in the Mediterranean Biodiversity hotspot where rising temperatures and drought are negatively affecting several plant taxa, including endemic species. Assisted colonisation (AC) represents a useful tool for reducing the effect of climate change on endemic plant species threatened by climate change.
We combined species distribution models (SDMs) for 188 taxa endemic to Italy with the IUCN red listing range loss threshold under criterion A (30%) to define: (a) the number of AC (measured as 2 × 2 km grid cells that should be occupied by new populations, i.e. grid cells = new populations) required to fully compensate for predicted range loss and to halt the decline below the 30% of range loss; (b) The number of cells necessary to compensate for range loss was calculated as the number of currently occupied cells lost under future climate due to unsuitable conditions. We used two representative concentration pathways, +2.6 and +8.5 W/m², optimistic and pessimistic scenarios respectively. Availability of suitable areas for AC was also assessed within the current species distribution and within protected areas.
Under the optimistic scenario, no taxa would lose more than 30% of their range and AC would not be required. Under the pessimistic scenario, roughly the 90% of taxa showed a cell loss higher than 30%. Eight taxa were predicted to lose >95% of their range. For these species, AC was required from 13 to 16 new populations (=13–16 grid cells) per taxon to cap the range loss at 30%. For currently VU or EN species, an average number of 32–35 AC attempts would be necessary to fully compensate their range loss under a pessimistic scenario. Suitable recipient sites within protected areas falling in their projected range were identified, allowing for short‐distance AC.
Synthesis. Combining species distribution models and red listing thresholds under Criterion A has enabled the strategic planning of multiple species assisted colonisation minimising the effort in terms of new populations to be created and maximising the conservation benefit in terms of range loss compensation.
... As the climate warms, increasing numbers of populations are located at the extreme ends of abiotic gradients (i.e., outside conditions they previously experienced), and the role of biotic interactions in determining realized distribution limits is gaining increased attention (e.g., HilleRisLambers et al. 2013;Brown and Vellend 2014;Hargreaves et al. 2014). Assisted translocation, the practice of moving members of threatened populations from less to more favorable environments to reduce extinction risk, is already occurring (e.g., Martín-Alcón et al. 2016). In studies of climate adaptation figure 4 (the scenario without adaptation is not shown, since no fitness differences exist). ...
The outcomes of many species interactions are conditional on the environments in which they occur. A common pattern is that outcomes grade from being more positive under stressful conditions to more antagonistic or neutral under benign conditions. The evolutionary implications of conditionality in interactions have received much less attention than the documentation of conditionality itself, with a few notable exceptions. Here, we predict patterns of adaptation and co-adaptation between partners along abiotic gradients, positing that when interactions become more positive in stressful environments, fitness outcomes for mutations affecting interactions align across partners and selection should favor greater mutualistic adap-tation and co-adaptation between interacting species. As a corollary, in benign environments, if interactions are strongly antagonistic, we predict antagonistic co-adaptation resulting in Red Queen or arms-race dynamics, or reduction of antagonism through character displacement and niche partitioning. We predict no adaptation if interactions are more neutral. We call this the CoCoA hypothesis: ( Co )-adaptation and Co nditionality across A biotic gradients. We describe experimental designs and statistical models that allow testing predictions of CoCoA, with a focus on positive interactions. While only one study has included all the elements to test CoCoA, we briefly review the literature and summarize study findings relevant to CoCoA and highlight opportunities to test CoCoA further.
... En les àrees amb episodis intensos de baixes temperatures cal evitar emprar espècies i procedències massa sensibles al fred. Per exemple, en el cas dels roures mediterranis, les espècies marcescents (per exemple, roure de fulla petita) tenen una més alta capacitat de tolerar condicions amb temperatures molt baixes que les espècies de fulla perenne, com ara l'alzina (Martín-Alcón et al., 2016). ...
Esteu llegint el recull de continguts de les vuit jornades del que ha estat la
XXXVI edició de les Jornades Tècniques Silvícoles Emili Garolera, que organitza
el Consorci Forestal de Catalunya.
Aquestes jornades, són trobades pràctiques a bosc, nascudes de la inquietud
de propietaris i gestors forestals per conèixer noves experiències de gestió
forestal, pensades per a esdevenir una finestra de coneixement aplicat i executades
per facilitar l’intercanvi d’experiències de gestió. A partir de la seva XIX
edició l’any 2001, es va apostar per a la seva tecnificació, organitzant jornades
amb un fort contingut tècnic però sense oblidar que aquesta tecnificació ha
d’estar al servei i disponible per als propietaris i gestors forestals. Amb els anys,
les Jornades han anat evolucionant en continguts i en participants. Cada any
intentem organitzar jornades que incorporin tècniques innovadores de gestió
i continguts d’actualitat amb el sector. Amb els anys, hem tingut èpoques on
bàsicament els participants eren propietaris i gestors forestals, altres èpoques
on s’hi afegien tècnics i enginyers forestals i durant uns anys vam estar
acompanyats d’estudiants dels diferents centres de formació forestal. Hi ha
hagut anys de més participació i anys de menys, com també hi ha jornades
amb més o menys participants i fins i tot, jornades que hem hagut de repetir
per donar resposta a la demanda d’assistència. L’any 2002 es va començar a
editar el recull de continguts de les diferents jornades proposades en cada
edició amb l’objectiu de consolidar en un llibre els continguts: primer en format
paper i a partir de l’any 2012 en format digital. En qualsevol cas, des de
l’organització de les Jornades Tècniques, sempre hem planificat les Jornades
com una activitat de formació pràctica (però amb un fons tecnificat) basada
en l’intercanvi i debat d’experiències, fet que ha portat aquesta iniciativa de
formació fins a esdevenir un reconegut referent pel que fa a promoció i divulgació
de silvicultura i gestió forestal aplicada a casa nostra.
I finalment i per acabar, sense que el fet de deixar-ho pel final impliqui menys
importància, arriben els agraïments. A les entitats i empreses que hi participen
i a les que hi col·laboren: la seva participació enriqueix els continguts
de les Jornades. Als ponents i coordinadors de les diferents Jornades: la
seva implicació garanteix els continguts tècnics. Als participants (propietaris
i gestors forestals, estudiants, tècnics independents, d’empreses privades i de
l’administració): sense tots ells les Jornades serien buides de contingut humà.
En aquest punt, cal un merescut reconeixement als propietaris forestals que
hi participen i hi col·laboren tot compartint el seu coneixement i experiència,
explicant i posant a debat la seva gestió davant d’un públic especialitzat.
Esperem que gaudiu de la lectura dels diferents articles que recullen l’expressió
escrita del coneixement i experiència divulgada en les diferents edicions i
Jornades, i que en un futur, us siguin d’utilitat per a la necessària gestió dels
boscos per assolir l’objectiu de la seva conservació i millora.
... Other studies found that the temporal changes in stand structure and plant composition in a forest ecosystem varied with the succession stage [96,97], and this change regulates the heterogeneity of light conditions through canopy closure [98,99] and edaphic features (e.g., the soil moisture content, pH, temperature, and nutrient availability) under the forest canopy [22,31,57,[100][101][102]. An uneven forest overstory weakens the adverse effects of seedling survival [103]. Individuals at different stages of development have different energy requirements, so a layered vertical structure can maximize the energy use at different heights, thus increasing species richness. ...
Climate, topography, and tree structure have different effects on plant diversity that vary with spatial scale. In this study, we assessed the contribution of these drivers and how they affect the vascular plant richness of different functional groups in a temperate forest ecosystem in Northeast China. We investigated about 0.986 million plants from 3160 sites to quantify the impact of annual mean temperature, sunshine duration, annual precipitation, standard deviation of diameter at breast height, and forest type on richness of vascular plants (total species, tree, treelet, shrub, and herb, separately) using the gradient boosting model. The results show that annual mean temperature had the strongest impact on plant richness. The tree richness peaked at intermediate annual mean temperature and sunshine duration and increased with annual precipitation. The Shannon diversity index and Simpson dominance index increased with annual precipitation and standard deviation of diameter at breast height, decreased with sunshine duration, and peaked at intermediate annual mean temperature and forest type. The total richness and understory richness increased with annual mean temperature and standard deviation of diameter at breast height and peaked at intermediate sunshine duration and annual precipitation. A comprehensive mechanism was found to regulate the plant diversity in forest ecosystems. The relationship between tree richness and annual mean temperature with latitudinal effect could be affected by the differences in number and size of tree individuals, indicating that plant diversity varies with the utilization of energy. The force driving plant richness varied with the functional group due to the different environmental resource requirements and the life history strategies of plants layers.
... En les àrees amb episodis intensos de baixes temperatures cal evitar emprar espècies i procedències massa sensibles al fred. Per exemple, en el cas dels roures mediterranis, les espècies marcescents (per exemple, roure de fulla petita) tenen una més alta capacitat de tolerar condicions amb temperatures molt baixes que les espècies de fulla perenne, com ara l'alzina (Martín-Alcón et al., 2016). ...
Aquest article presenta i discuteix l’interès de les plantacions d’enriquiment per fomentar
la sostenibilitat tècnica (persistència), econòmica i ambiental de les masses forestals.
Aquestes plantacions consisteixen a introduir o incrementar la proporció d’una o més
espècies en una forest preexistent. Aquesta mesura té tres objectius principals, compatibles
entre si: afavorir l’adaptació al canvi climàtic i a les pertorbacions associades,
diversificar i valoritzar els productes forestals i promoure la biodiversitat. Aquestes plantacions
són especialment interessants en àrees forestals homogènies de gran extensió
(regenerats naturals després d’incendi o d’abandonament agrícola/ramader, repoblacions
pures, etc), boscos de baix vigor, àrees amb (micro)estacions d’alta qualitat però
baixa presència d’espècies amb alt valor productiu, així com a boscos amb problemes
de regeneració natural, entre d’altres. Aquest article presenta una sèrie de condicionants
per implementar aquestes plantacions i es fan recomanacions pràctiques per al
seu disseny, execució i manteniment. Per últim, es presenten casos reals de plantacions
d’enriquiment en pinedes de pi blanc i pinassa a l’Anoia i el Penedès
... Strategies aimed at promoting changes in forest composition towards species or genotypes better adapted to the conditions forecasted under future climates. These strategies can include actions in-situ by using extant species or exsitu by using assisted-migration(Martín-Alcón et al., 2016;Mason and Connolly, 2014 ...
As global climate becomes warmer, the maintenance of the structure and function of Mediterranean forests constitutes a key challenge to forest managers. Despite the need for forest adaptation, an overall evaluation of the efficacy of current management strategies is lacking. Here we describe a theoretical framework for classifying management strategies, explicitly recognizing trade-offs with other, untargeted ecosystem components. We then use this framework to provide a quantitative synthesis of the efficacy of management strategies in the Mediterranean basin. Our review shows that research has focused on strategies aimed at decreasing risk and promoting resistance in the short-term, rather than enhancing long-term resilience. In addition, management strategies aiming at short-term benefits frequently have unintended consequences on other adaptation objectives and untargeted ecosystem components. Novel empirical studies and experiments focusing both on adaptation objectives and multiple responses and processes at the ecosystem level are needed. Such progress is essential to improve the scientific basis of forest management strategies and support forest adaptation in the Mediterranean basin.
... Nonetheless, the support for assisted migration by such studies is as inconsistent as that found for the definitive tests above (e.g. Lu et al. 2014;Grady et al. 2015;Benomar et al. 2016;Martín-Alcón et al. 2016;Taïbi et al. 2016) In summary, while there are good reasons to expect strong and possibly negative effects of assisted migration on biotic interactions, there is little evidence that such actions will actually improve plant performance and enhance ecosystem services. Despite the lack of clear evidence, journals keep publishing reviews and perspective papers where authors state that assisted migration is a promising and possibly necessary approach (Aitken & Whitlock 2013;Gallagher et al. 2015;Klenk 2015;Koralewski et al. 2015;Aitken & Bemmels 2016;Breed et al. 2016;Christmas et al. 2016), leading to propagation among practitioners and incorporation into guidelines (McDonald et al. 2016;Sansilvestri et al. 2016). ...
In the context of climate change, many plant species may have problems adapting or dispersing rapidly enough to keep pace with changing environmental conditions. Given these potential problems, some experts argue against using local plant ecotypes for ecosystem restoration. Instead, they propose to use foreign ecotypes that are adapted to the predicted climate in an approach called assisted migration within species range or predictive provenancing. I argue that such actions may cause a mismatch in biotic interactions and have negative effects on other organisms. As such, assisted migration should only be considered in cases when the local ecotypes would fail to ensure ecosystem services. In fact, there is little experimental evidence on the assisted migration approach so far, and what little there is does not seem to support its use. Even in altered climates, local ecotypes mostly performed equally well or better than foreign ones selected for their adaptations to these climates. The reason is that even if adaptation to climate plays a role, this factor may be overridden by other drivers of local adaptation, such as soil or biotic interactions. Despite assisted migration being a popular concept that is repeatedly commended in scientific literature and propagated among practitioners, it should not be considered a universal tool to improve restoration outcomes during climate change. Given the lack of hard experimental data, I call for large-scale multispecies experimental studies that will provide the necessary evidence to derive general guidelines and recommendations for management of ecosystems during climate change.
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.
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.
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.
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.
Given projected rates of climate change, species with limited dispersal may be unable to migrate at the pace necessary to maintain their current climate niches. This could lead to increased risk of extirpation or extinction, especially for locally range-restricted species within fragmented landscapes. Assisted migration has been suggested as a proactive conservation tool to mitigate these risks. We tested assisted migration for Liatris ligulistylis and Houstonia longifolia, two perennial forbs considered ‘vulnerable’ and ‘imperilled’ respectively, in Alberta, Canada, where they are at their northern and western range limits. Both mature plants and seeds were translocated to replicate sites at four geographic locations along a north-south gradient representing the current ranges of the species (central) and areas south (warmer) and north (cooler) of their current range. L. ligulistylis adult plants thrived ∼500 km north of the species current range with survival, growth, and flowering similar to or exceeding performance in the current range, the influence of soil was also tested by comparing the performance of transplanted mature plants in soil from the source location versus the translocation (recipient) site. Plants planted into soil from the source location had increased flower bud production at all sites. Seedling establishment was significantly higher at sites north of the current range, but much lower in the southern locations. These results suggest that L. ligulistylis is in climate disequilibrium, potentially due to migration lags, and that it might be vulnerable to near-future climate vulnerability. For H. longifolia, the influence of flower morph type and location were tested. Only 8 out 130 translocated adult plants survived, five with thrum flowers and three with pin flowers; no seedling establishment was observed in the first growing season, which experienced drier than normal conditions. Among the eight adult plants, seven survived in the central location and one in the north demonstrating specific habitat requirements and conditions that may make this species difficult for translocation and establishment. Overall, locally rare and range-restricted plants with limited dispersal demonstrate climate sensitivity to current conditions and potential for assisted migration, yet species-by-species testing is needed to understand vulnerability and efficacy of this approach.
The outcomes of many species interactions are conditional on the environments in which they occur. Often, interactions grade from being more positive under stressful or low-resource conditions to more antagonistic or neutral under benign conditions. Here, we take predictions about two well-supported ecological theories on conditionality-limiting resource models and the stress-gradient hypothesis-and combine them with those from the geographic mosaic theory of coevolution (GMTC) to generate predictions for systematic patterns of adaptation and coadaptation between partners along abiotic gradients. When interactions become more positive in stressful environments, mutations that increase fitness in one partner may also increase fitness in the other; because fitnesses are aligned, selection should favor greater mutualistic adaptation and coadaptation between interacting species in stressful ends of environmental gradients. As a corollary, in benign environments antagonistic coadaptation could result in Red Queen or arms-race dynamics or the reduction of antagonism through character displacement and niche partitioning. Here, we distinguish between generally mutualistic or antagonistic adaptation (i.e., mutations in one partner that have similar effects across multiple populations of the other) and specific adaptations to sympatric partners (local adaptation), which can occur either alone or simultaneously. We then outline the kinds of data required to test these predictions, develop experimental designs and statistical methods, and demonstrate these using simulations based on GMTC models. Our methods can be applied to a range of conditional outcomes and may also be useful in assisted translocation approaches in the face of climate change.
Over the past 15 years, 3 million hectares of forests have been converted into shrublands or grasslands in the Mediterranean countries of the European Union. Fire and drought are the main drivers underlying this deforestation. Here we present a conceptual framework for the process of fire-induced deforestation based on the interactive effects of fire and drought across three hierarchical scales: resistance in individuals, resilience in populations, and transitions to a new state. At the individual plant level, we review the traits that confer structural and physiological resistance, as well as allow for resprouting capacity: deforestation can be initiated when established individuals succumb to fire. After individuals perish, the second step toward deforestation requires a limited resilience from the population, that is, a reduced ability of that species to regenerate after fire. If individuals die after fire and the population fails to recover, then a transition to a new state will occur. We document trade-offs between drought survival and fire survival, as embolism resistance is negatively correlated with fire tolerance in conifers and leaf shedding or drought deciduousness, a process that decreases water consumption at the peak of the dry season, temporally increases crown flammability. Propagule availability and establishment control resilience after mortality, but different hypotheses make contrasting predictions on the drivers of post-fire establishment. Mycorrhizae play an additional role in modulating the response by favoring recovery through amelioration of the nutritional and water status of resprouts and new germinants. So far, resprouter species such as oaks have provided a buffer against deforestation in forests dominated by obligate seeder trees, when present in high enough density in the understory. While diversifying stands with resprouters is often reported as advantageous for building resilience, important knowledge gaps exist on how floristic composition interacts with stand flammability and on the "resprouter exhaustion syndrome," a condition where pre-fire drought stress, or short fire return intervals, seriously restrict post-fire resprouting. Additional attention should be paid to the onset of novel fire environments in previously fire-free environments, such as high altitude forests, and management actions need to accommodate this complexity to sustain Mediterranean forests under a changing climate.
Over the past 15 years, 3 million hectares of forests have been converted into shrublands or grasslands in the Mediterranean countries of the European Union. Fire and drought are the main drivers underlying this deforestation. Here we present a conceptual framework for the process of fire-induced deforestation based on the interactive effects of fire and drought across three hierarchical scales: resistance in individuals, resilience in populations, and transitions to a new state. At the individual plant level, we review the traits that confer structural and physiological resistance, as well as allow for resprouting capacity: deforestation can be initiated when established individuals succumb to fire. After individuals perish, the second step toward deforestation requires a limited resilience from the population, that is, a reduced ability of that species to regenerate after fire. If individuals die after fire and the population fails to recover, then a transition to a new state will occur. We document trade-offs between drought survival and fire survival, as embolism resistance is negatively correlated with fire tolerance in conifers and leaf shedding or drought deciduousness, a process that decreases water consumption at the peak of the dry season, temporally increases crown flammability. Propagule availability and establishment control resilience after mortality, but different hypotheses make contrasting predictions on the drivers of post-fire establishment. Mycorrhizae play an additional role in modulating the response by favoring recovery through amelioration of the nutritional and water status of resprouts and new germinants. So far, resprouter species such as oaks have provided a buffer against deforestation in forests dominated by obligate seeder trees, when present in high enough density in the understory. While diversifying stands with resprouters is often reported as advantageous for building resilience, important knowledge gaps exist on how floristic composition interacts with stand flammability and on the “resprouter exhaustion syndrome,” a condition where pre-fire drought stress, or short fire return intervals, seriously restrict post-fire resprouting. Additional attention should be paid to the onset of novel fire environments in previously fire-free environments, such as high altitude forests, and management actions need to accommodate this complexity to sustain Mediterranean forests under a changing climate.
Reforestation is common to restore degraded ecosystems, but tree-species choice often neglects ongoing environmental changes. We evaluated the performance of planted seedlings of two oak species at two sites in a Mediterranean mountain (Sierra Nevada, SE Spain): one located within the current altitudinal forest range (1,600–1,760 m), and one above the upper forest limit (1,970–2,120 m). The forest service planted 1,350 seedlings of the deciduous Pyrenean oak and the evergreen Holm oak in a postfire successional shrubland. After 2 years, seedlings were monitored for survival, and a subset of 110 Pyrenean oaks and 185 Holm oaks were harvested for analyses of biomass and foliar nutrient status, í µí¼¹ 13 C, and í µí¼¹ 18 O. Both species showed the highest survival and leaf N status above the upper forest limit, and survival increased with altitude within each plot. The deciduous oak benefited most from planting at higher altitude, and it also had greater biomass at the higher site. Correlations between foliar N, í µí¼¹ 18 O, and í µí¼¹ 13 C across elevations indicate tighter stomatal control of water loss and greater water-use efficiency with increasing plant N status at higher altitude, which may represent a so-far overlooked positive feedback mechanism that could foster uphill range shifts in water-limited mountain regions. Given ongoing trends and future projections of increasing temperature and aridity throughout the Mediterranean region, tree-species selection for forest restoration should target forecasted climatic conditions rather than those prevailing in the past. This study highlights that ecosystem restoration provides an opportunity to assist species range shifts under rapidly changing climate.
One approach to compensating for rapid climate change and protecting biodiversity is assisted migration (AM) of key tree species. However, tools for evaluating the sensitivity of target sites and identifying potential sources have not yet been developed. We used the National Forest Inventories of Spain and France to design scenarios for AM between and within both countries. We characterized sensitivity to climate change as the expected changes in volume and mortality of Pinus halepensis Miller and Pinus pinaster Aiton between the present and 2050. Target zones were selected from provenances with high sensitivity and seed zones from provenances with low sensitivity to climate change; the latter can be considered ''seed refugia'' as the climate changes. Three plausible scenarios for translocation to the target zone were developed on the basis of volume simulations calibrated with different planting strategies: (1) seeds only from foreign provenances; (2) foreign provenances plus local seeds; and (3) only local seeds. The results for both species show that models based on foreign ''top-three'' provenances always increased the standing volume of the target zone. Models run with only local seeds predicted increased volume for P. halepensis but not for P. pinaster. Our results suggest that volume and mortality trends are not always correlated with seed sources and targets, that projected provenances mortality do not follow always a southern–northern pattern and that seed
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.
Temperate climates are defined by distinct temperature seasonality with large and often unpredictable weather during any of the four seasons. To thrive in such climates, trees have to withstand a cold winter and the stochastic occurrence of freeze events during any time of the year. The physiological mechanisms trees adopt to escape, avoid, and tolerate freezing temperatures include a cold acclimation in autumn, a dormancy period during winter (leafless in deciduous trees), and the maintenance of a certain freezing tolerance during dehardening in early spring. The change from one phase to the next is mediated by complex interactions between temperature and photoperiod. This review aims at providing an overview of the interplay between phenology of leaves and species-specific freezing resistance. First, we address the long-term evolutionary responses that enabled temperate trees to tolerate certain low temperature extremes. We provide evidence that short term acclimation of freezing resistance plays a crucial role both in dormant and active buds, including re-acclimation to cold conditions following warm spells. This ability declines to almost zero during leaf emergence. Second, we show that the risk that native temperate trees encounter freeze injuries is low and is confined to spring and underline that this risk might be altered by climate warming depending on species-specific phenological responses to environmental cues.
Background and aims:
Several studies show apparently contradictory findings about the functional convergence within the Mediterranean woody flora. In this context, this study evaluates the variability of functional traits within holm oak (Quercus ilex) to elucidate whether provenances corresponding to different morphotypes represent different ecotypes locally adapted to the prevaling stress levels.
Methods:
Several morphological and physiological traits were measured at leaf and shoot levels in 9-year-old seedlings of seven Q. ilex provenances including all recognized morphotypes. Plants were grown in a common garden for 9 years under the same environmental conditions to avoid possible biases due to site-specific characteristics.
Key results:
Leaf morphometry clearly separates holm oak provenances into 'ilex' (more elongated leaves with low vein density) and 'rotundifolia' (short and rounded leaves with high vein density) morphotypes. Moreover, these morphotypes represent two consistent and very contrasting functional types in response to dry climates, mainly in terms of leaf area, major vein density, leaf specific conductivity, resistance to drought-induced cavitation and turgor loss point.
Conclusions:
The 'ilex' and 'rotundifolia' morphotypes correspond to different ecotypes as inferred from their contrasting functional traits. To the best of our knowledge, this is the first time that the combined use of morphological and physiological traits has provided support for the concept of these two holm oak morphotypes being regarded as two different species.
In the context of climatic changes, the adaptive potential of organisms toward new environmental challenges is becoming of central interest in modern ecology. Here we investigate the response of growth haracteristics and survival in juveniles of four European provenances (Bulgaria, Germany, Hungary and Italy) of Quercus pubescens Willd. to extreme drought and warming in a full factorial common garden experiment. Our results show that extreme durations of drought exceed the tolerance of Quercus pubescens of all provenances. Plants of Italian provenance showed the highest capacity of whole-individual survival, and those of Bulgarian
provenance showed the highest maintenance of the apex under extreme drought. Bud bank characteristics showed no general differences among provenances but responded to warming manipulations. The warming effect resulted in a reduction of collar buds and biomass. In Italian individuals it caused an increase of the apical budbank. This is suggestive of a better adaptation for height growth under warming. Our results imply that significant local adaptation of growth characteristics and survival occurs in Quercus pubescens. However, our findings do not support the idea that southern provenances are a general predictor of better plant performance.
Assisted migration (AM) id often presented as a strategy to save species that are imminently threatened by rapid climate change. This conception of AM, which has generated considerable controversy, typically proposes the movement of narrowly distributed, threatened species to suitable sites beyond their current range limits. However, existing North American forestry operations present an opportunity to practice AM on a larger scale, across millions of hectares, with a focus on moving populations of widely distributed, nonthreatened tree species within their current range limits. Despite these differences (and many others detailed herein), these two conceptions of AM have not been clearly distinguished in the literature, which has added confusion to recent dialogue and debate. Here, we aim to facilitate clearer communication on this topic by detailing this distinction and encouraging a more nuanced view of AM.
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.
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.
Restoration programs need to increasingly address both the restitution of biodiversity and ecosystem services and the preparation of habitats for future climate change. One option to adapt habitats to climate change in the temperate zone is the translocation of southern populations to com-pensate for climate change effects—an option known as assisted migration (AM). Although AM is widely criticized for endangered species, forest managers are more confi-dent that tree populations can be translocated with suc-cess because of previous experiences within native ranges. Here, we contend that translocations of tree populations are also subject to uncertainties, and we extract lessons for future programs of AM within species ranges from a well-documented failed case of population translocation of Pinus pinaster Ait. in Europe. The failure of these translocations originated from the unawareness of several unpredictable ecological and social events: cryptic mal-adaptation of the introduced populations, underestimation of climate variability differences between the source and target sites, and complexity in the management schemes, postponing decisions that could have been undertaken ear-lier. Under the no-analog conditions that are expected with climate change, management decisions need to be made with incomplete data, implying that a certain degree of maladaptation should always be expected when restoring plant populations from local or external seed sources.
Encroachment of trees into low-productivity grasslands is a serious threat to grassland biodiversity throughout Europe. Although the rate of encroachment of trees into grassland is variable and poorly understood, it is thought to result from variation in tree seedling recruitment, which is limited mainly by the availability of safe sites and the dispersal distances of propagules. In this study, we established spatially explicit models of seedling recruitment for two major sub-Mediterranean trees: Quercus pubescens Willd. and Fagus sylvatica L. We quantified the spatial distribution of Q. pubescens and F. sylvatica seedlings up to 20 years old at three grassland sites. We also quantified the spatial distribution and size of mature trees and of the two dominant species of shrubs, Buxus sempervirens L. and Juniperus communis L., at each of the three sites. Ninety-eight percent of the regeneration took place under shrub canopy. Quercus pubescens seedlings showed higher seedling production per unit of canopy area and longer mean effective dispersal distances than did F. sylvatica seedlings. Quercus pubescens seedlings also had a large advantage over F. sylvatica seedlings for establishment in open areas. Juniperus shrubs were better safe sites for the establishment of Q. pubescens and F. sylvatica seedlings than were Buxus shrubs. We calculated indices of seedling dispersal limitation and safe site availability for recruitment for four dates. In the dolomitic Causse grasslands examined in this study, the availability of safe sites for germination and survival was far more important than seedling dispersal limitation for recruitment of both tree species.
Ecological processes within forests provide vital ecosystem services to society, most of which depend on the persistence of tree cover that can be altered after the impact of a disturbance. The aim of the present study was to examine the role of seed dispersal and resprouting that mediate resilience to large fires and evaluate the economic costs that these ecological functions provide. We used field data from 412 plots of the Spanish National Forest Inventory providing information on pre- and post-fire conditions of Mediterranean Pinus spp. and Quercus spp.-dominated forests. Then, we determined the need for restoration (N
Rest) and estimated the minimum pre-fire densities needed to ensure adequate post-fire cover. Economic valuations were assessed through three different scenarios (Sc) of possible human-management actions aimed at ensuring proper post-fire tree cover: Sc. 1) a pre-fire management scenario evaluating the costs of planting Quercus spp. seedlings in the understory, mimicking the whole dispersal function; Sc. 2) a pre-fire scenario in which enrichment plantations increased the densities of natural oaks; and Sc. 3) a post-fire scenario where the restoration is done through planting pines within the burned area. Approximately 90% of the burned area (371 out of 412 plots) was able to recover after fire supporting the view that Mediterranean forests are resilient to fire. This resilience was primarily mediated by biotic seed dispersal and posterior resprouting of tree species. These ecological functions saved between 626 and 1,326 €/ha compared to the human-management actions. Ensuring key ecological processes within forests increases forest resilience and recovery after fire leading to a generally significant saving of economic resources. In a perspective of increased future impact of disturbances and decrease availability of economic resources for forest management, the implications of the present study can be far reaching and extended to other forest planning exercises.
Spatial heterogeneity of abiotic factors influences patterns of seedling establishment at different scales. In stress-prone ecosystems such as Mediterranean ones, heterogeneity generated by shrubs has been shown to facilitate the establishment of tree species. However, how this facilitation is affected by spatial scale remains poorly understood. We have experimentally analysed the consequences of the abiotic heterogeneity generated by pioneer shrubs on survival, growth and physiology of seedlings of three important tree species from Mediterranean mountains (Acer opalus ssp. granatense, Quercus pyrenaica and Quercus ilex). Patterns of abiotic heterogeneity and seedling performance were studied at two scales differing in grain: 1) the microhabitat scale, by using open interspaces as controls of the effect of different shrub species, and 2) the microsite scale, analysing the effects of fine-grain heterogeneity (within-microhabitat heterogeneity). Results showed that, at the microhabitat scale, seedling establishment of the three tree species significantly benefited from the modification of the abiotic environment by nurse shrubs. However, we found shrub-seedling interactions to be species-specific, due to differential modification of both aboveground (light availability) and belowground (soil compaction, water content, and fertility) abiotic factors by nurse shrub species. Heterogeneity at the within-microhabitat scale was rather high, although it did not significantly affect seedling performance of any of the tree species. The study demonstrates that the effects of the abiotic heterogeneity generated by shrubs are not consistent across the range of spatial scales considered. The regeneration niche of tree species becomes very complex at fine spatial scales, and thereby estimators of abiotic heterogeneity are valuable descriptors of spatial patterns of seedling establishment only when microsite "noise" is averaged out at greater scales.
Mediterranean forest plantations are currently under an intense debate related to their ecological function, sustainability and future performance. In several Mediterranean countries, efforts are directed to convert pine plantations into mixed and more diverse forests. This research aims to evaluate the effect of the spatial configuration of pine plantations on regeneration and plant diversity in order to facilitate plantation management towards more diversified stands. Spatial characteristics of plantations (proximity to different vegetation types, fragmentation and internal patch structure) were related to abundance of seedlings of an ecologically important broadleaved species, Holm Oak (Quercus ilex L.), and the Shannon diversity index of the community. Q. ilex seedling abundance and plant diversity in pine plantation patches are favoured by the proximity to oak patches located uphill. Fragmentation affected only plant diversity, with smaller patches having more diversity. The internal structure of the pine patch influenced both regeneration of Q. ilex and diversity. Pine patches with lower pine tree density were characterized by higher diversity and less Q. ilex regeneration confirming that internal structure affects species differently. From a management perspective, the process of conversion of Mediterranean pine plantations to mixed oak–pine forests could be facilitated by (1) having the seed source uphill from the plantation, (2) increasing the fragmentation of plantations and (3) promoting the internal heterogeneity of plantations to create a diverse range of light environments matching the different requirements of species.
Despite evidences that Holm oak has a high plasticity and great adaptability, there is limited or contradictory knowledge of the morphological and physiological variability of this species. Holm oak has been widely used for reforestation projects in Mediterranean areas, but has frequently shown poor field performance. We hypothesized that Holm oak has inter-population differences in physiological responses to abiotic stressors that could affect reforestation success. The influence of nursery culture on the characteristics of Holm oaks from different provenances has not been explored in depth. Thus, we studied the effect of nursery autumn fertilization on morphological traits, frost tolerance, root growth potential, and nutritional status of two Spanish provenances of Holm oak, La Alcarria (a region with inland Mediterranean climate) and Sierra Morena Occidental (a region with a warm coastal Mediterranean climate). There were significant differences between the provenances in frost tolerance, biomass allocation, and leaf nutrient content, suggesting a role of genetic factors. The leaves of seedlings from La Alcarria had less visual damage at -12ºC than seedlings from the warmer provenance (45% vs 92%). Seedlings from La Alcarria, compared to those from Sierra Morena, had higher leaf P concentration (0.17% vs 0.15%), greater stem diameter (3.1 mm vs 2.7 mm), lower shoot-to-root dry mass ratio (0.46 vs 0.53), and lower slenderness (4.03 vs 5.31). For both provenances, N autumn fertilization improved growth, root growth potential, cold hardiness, and nutritional status of seedlings. We suggest that forest reforestation programs should consider to a greater extent Holm oak provenances and their tolerances to different abiotic stressors.
A broad-scale analysis of the structure and understory composition of Pyrenean mountain pine (Pinus uncinata Ram.) stands was performed using data from the Spanish National Forest Inventory. Twelve structure-based forest typologies were defined from variables related to tree size, stand density, vertical structure and standing deadwood, using cluster
analysis techniques. These typologies were adequately classified (accuracy >75 per cent) by a dichotomous key obtained from classification and regression trees. Multiple regression models were then used to analyse relationships between the main stand structural variables and a set of climatic and physiographic factors. The models showed significant correlations between winter temperature, slope and continentality (among other variables) and the current structure of mountain pine stands. The relationships between the understory composition of mountain pine forests and different environmental and structural overstory factors were found to be driven by an elevation-pH gradient and a stand
density-soil stoniness gradient. The results of this study can be directly used for forest planning at different scales and could help forest managers to establish strategies designed to facilitate a given habitat for species of conservation interest.
Common garden testing of populations of different origin started with forest trees more than two hundred years ago. Since then, so-called provenance tests have been established with most commercially important species. Beyond the strictly silvicultural goals, the tests offer excellent opportunities to study intraspecific genetic variation patterns and represent probably the most powerful available tool for testing hypotheses of climatic adaptation in trees.
Analysis of adaptive traits (mostly juvenile height growth) in provenance experiments indicate the existence of very effective constraints on adaptedness. The performance of populations plotted against an ecological-climatic factor exhibits a characteristic pattern and can be described by response functions. The population average of a fitness-related trait for a locally adapted population is often significantly lower than that of populations from other environments; usually the ones from milder climate perform better. The phenomenon is interpreted as adaptation lag. Suboptimal adaptation is compensated by a high level of genetic diversity. Molecular genetic studies confirm the high level of allelic and individual genetic diversity in forest trees. A consequence of individual homeostasis, phenotypic stability of populations is usually also high; the sensitivity to environmental changes is generally moderate. Phenotypically stable populations are valuable not only because of a wider range of potential cultivation but specifically because of a greater ability to adjust to unexpected changes. This trait should receive more attention in the future for obvious reasons.
The maintenance of a high within-population genetic variance is favored by the genetic system of the investigated species (effective gene flow, outbreeding, high genetic load, etc.). Random events and long-lasting biotic interactions are further effects impairing the efficiency of natural selection.
In view of expected climate instability, genetic adaptability of forest trees causes serious concern due to their long lifespan compared to the rapidity of expected changes in environmental conditions. The potential of provenance tests to interpret long-term adaptational processes should be utilized to analyze, model and predict response of trees to climate change. Although seldomly appreciated, provenance research might be among the most important contributions of forestry to biological sciences.
Introduction
The limited ability of Quercus species to regenerate naturally in Mediterranean forests has led to the development of various artificial regeneration methods; however, there is no general consensus as to what specific method is the best one for this purpose.
Material and methods
In this work, we assessed morphology, growth and survival of two Quercus species (Quercus ilex ssp. ballota and Quercus suber) using two different methods of artificial regeneration (viz. direct seeding and planting) and two seedling ages (1-year-old seedlings and 3-year-old seedlings) in southern Spain.
Results and discussion
The 1-year-old seedlings of both species were found to exhibit the highest survival percentages and direct-seeded plants intermediate survival values. For direct-seeded plants, seed mass was found to have a significantly positive effect on the establishment success in both species. No clear-cut trend in survival was detected in the 3-year-old seedlings. The survival of the 3-year-old Q. suber seedlings and the direct-seeded plants was similar, but not in Q. ilex, where the survival of the 3-year-old seedlings was the lowest. The latter result may have been a consequence of cultivation in smaller containers leading to root deformation and limiting plant access to water. Differences in survival could not be ascribed to morphological and growth variables or stomatal conductance.
Conclusion
Based on the results, all three artificial regeneration methods can be similarly effective provided appropriate nursery cultivation conditions are used and seeds are protected against predators, the best choice in each case being dictated by the particular restoration goals.
The goal of this study was to develop management strategies favouring establishment and survival of holm oak (Quercus ilex L.) and downy oak (Quercus pubescens Willd.)—two species co-occurring in Southern France—in mature Allepo pine forests (Pinus halepensis Mill subsp. halepensis). An experimental design was assessed in a partially cut mature stand of Aleppo pine in which five soil and vegetation treatments—chopping,
chopping followed by scarification in one or two directions, prescribed burning, control—and two slash treatments (presence/absence)
were applied. A total of 1,600 sowing points, each composed of 3 Q. ilex or Q. pubescens acorns, were installed in the different treatments in November of two consecutive years at 6 and 18months, after the end
of treatments. Survival was monitored 3 and 2years after sowing, soil surface at the sowing points was characterized at different
dates, and predawn leaf water potentials were measured during the dry season. High mortality occurred after the first summer,
but survival after 1year was 2.3–5.2 higher in Q. ilex than in Q. pubescens, confirming that Q. ilex was better adapted to the drier parts of the Mediterranean area. Survival was significantly influenced by the treatments,
but there was a variable response between the two sowing years under most of the treatments. Only intense fire proved the
most beneficial treatment for seedling survival in both years. The micro-local soil cover conditions induced by the treatments
played a major role in explaining oak survival. In particular, grass cover (mainly Brachypodium retusum) proved to be largely unfavourable to seedling survival and growth, and this detrimental effect was also confirmed by lower
predawn leaf water potential values with increasing grass cover. Acorn introduction designed to diversify mature Aleppo pine
forest after soil and vegetation treatments therefore has to be considered for treatments that most efficiently impair the
pre-existing competing grass cover such as prescribed high-intensity fire treatment.
KeywordsMediterranean oaks-Seedling survival-Seedling growth-Prescribed burning-Stand regeneration-Vegetation control
This is a book for statistical practitioners, particularly those who design and analyze studies for survival and event history data. Its goal is to extend the toolkit beyond the basic triad provided by most statistical packages: the Kaplan-Meier estimator, log-rank test, and Cox regression model. Building on recent developments motivated by counting process and martingale theory, it shows the reader how to extend the Cox model to analyse multiple/correlated event data using marginal and random effects (frailty) models. It covers the use of residuals and diagnostic plots to identify influential or outlying observations, assess proportional hazards and examine other aspects of goodness of fit. Other topics include time-dependent covariates and strata, discontinuous intervals of risk, multiple time scales, smoothing and regression splines, and the computation of expected survival curves. A knowledge of counting processes and martingales is not assumed as the early chapters provide an introduction to this area. The focus of the book is on actual data examples, the analysis and interpretation of the results, and computation. The methods are now readily available in SAS and S-Plus and this book gives a hands-on introduction, showing how to implement them in both packages, with worked examples for many data sets. The authors call on their extensive experience and give practical advice, including pitfalls to be avoided. Terry Therneau is Head of the Section of Biostatistics, Mayo Clinic, Rochester, Minnesota. He is actively involved in medical consulting, with emphasis in the areas of chronic liver disease, physical medicine, hematology, and laboratory medicine, and is an author on numerous papers in medical and statistical journals. He wrote two of the original SAS procedures for survival analysis (coxregr and survtest), as well as the majority of the S-Plus survival functions. Patricia Grambsch is Associate Professor in the Division of Biostatistics, School of Public Health, University of Minnesota. She has collaborated extensively with physicians and public health researchers in chronic liver disease, cancer prevention, hypertension clinical trials and psychiatric research. She is a fellow the American Statistical Association and the author of many papers in medical and statistical journals.
Processes operating during the seed, seedling and juvenile phases are crucial for understanding patterns, dynamics and succession in plant communities (Schupp 1990; Grime and Hillier 1992). Many recent studies in temperate forests have emphasized the difficulties seedlings encounter in establishing themselves and the problems hardwood tree species face for survival, in particular the species of the genus Quercus (Lorimer 1984; Ross et al. 1986; Crow 1988, 1992; Johnson 1992; Keeley 1992; Ward 1992). This apparent paradox presented by late-successional species which, while dominant in the landscape, do not regenerate easily has long been noticed (Crow 1988), but the reasons for this are still poorly understood. The reasons for failure to recruit may include many factors, such as adequacy of seed dispersal (McClanahan 1986; Willson 1992), seed predation by animals (Crawley 1992), abiotic stresses such as drought or light limitation (Pons 1992; Espelta et al. 1995), and availability of suitable microsites for seed germination and seedling establishment (Crawley 1990). Furthermore, the regeneration failure of recent oak forests has also been attributed to the fact that the distribution of oaks overlaps to a large extent zones of intense human activity and thus oak forests have suffered from human impact (Matsuda et al. 1989).
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.
Introduction.- Estimating the Survival and Hazard Functions.- The Cox Model.- Residuals.- Functional Form.- Testing Proportional Hazards.- Influence.- Multiple Events per Subject.- Frailty Models.- Expected Survival.
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.
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.
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.
This paper analyses changes in plant cover in a valley of the Spanish Central Pyrenees during the second half of the 20th century. The role played by the extensification of farming activities in this process has been examined. The method used was based on evolutionary mapping of the plant cover, application of landscape indices and spatial analysis of livestock pressure. Throughout the century the stocking rate in the valley has decreased dramatically and sheep have been replaced by cattle. Most crop areas have been abandoned, and these areas have gone through a revegetation process (involving both natural vegetation and forest plantation). Nowadays the forest is the most abundant element. The study shows that both agricultural set-aside and the stocking rate decrease have led to a more natural landscape. Finally, the positive and negative effects of extensification and the changes in vegetation patterns associated with it are debated.
Mixed-effects models have become a popular approach for the analysis of grouped data that arise in many areas as diverse as clinical trials, epidemiology, and sociology. Examples of grouped data include longitudinal data, repeated measures, and multilevel data. In the case of linear mixed-effects (LME) models, the likelihood function can be expressed in closed form, with efficient computational algorithms having been proposed for maximum likelihood and restricted maximum likelihood estimation. For nonlinear mixed-effects (NLME) models and generalized linear mixed models (GLMMs), however, the likelihood function does not have a closed form. Different likelihood approximations, with varying degrees of accuracy and computational complexity, have been proposed for these models. This article describes algorithms for one such approximation, the adaptive Gaussian quadrature (AGQ), for GLMMs which scale up efficiently to multilevel models with arbitrary number of levels. The proposed algorithms greatly reduce the computational complexity and the memory usage for approximating the multilevel GLMM likelihood, when compared to a direct application of a single-level AGQ approximation algorithm to the multilevel case. The accuracy of the associated estimates is evaluated and compared to that of estimates obtained from other approximations via simulation studies.
The analysis of censored failure times is considered. It is assumed that on each individual are available values of one or more explanatory variables. The hazard function (age-specific failure rate) is taken to be a function of the explanatory variables and unknown regression coefficients multiplied by an arbitrary and unknown function of time. A conditional likelihood is obtained, leading to inferences about the unknown regression coefficients. Some generalizations are outlined. LIFEtables are one of the oldest statistical techniques and are extensively used by medical statisticians and by actuaries. Yet relatively little has been written about their more formal statistical theory. Kaplan and Meier (1958) gave a comprehensive review of earlier work and many new results. Chiang in a series of papers has, in particular, explored the connection with birth-death processes; see, for example, Chiang (1968). The present paper is largely concerned with the extension of the results of Kaplan and Meier to the comparison of life tables and more generally to the incorporation of regression-like arguments into life-table analysis. The arguments are asymptotic but are relevant to situations where the sampling fluctuations are large enough to be of practical importance. In other words, the applications are more likely to be in industrial reliability studies and in medical statistics than in actuarial science. The procedures proposed are, especially for the two-sample problem, closely related to procedures for combining contingency tables; see Mantel and Haenzel (1959), Mantel (1963) and, especially for the application to life tables, Mantel (1966). There is also a strong connection with a paper read recently to the Society by R. and J. Peto (1972). We consider a population of individuals; for each individual we observe either the time to "failure" or the time to ccloss" or censoring. That is, for the censored individuals we know only that the time to failure is greater than the censoring time. Denote by T a random variable representing failure time; it may be discrete or continuous. Let F(t) be the survivor function, %(t) = pr (T2 t)
The analysis of censored failure times is considered. It is assumed that on each individual are available values of one or more explanatory variables. The hazard function (age‐specific failure rate) is taken to be a function of the explanatory variables and unknown regression coefficients multiplied by an arbitrary and unknown function of time. A conditional likelihood is obtained, leading to inferences about the unknown regression coefficients. Some generalizations are outlined.
Assisted colonization (AC), or the intentional transloca-tion of populations to compensate for risks related to climate change, is receiving increasing attention. It has been recently suggested by Kreyling et al. (2011) that rather than relocating endangered species, a focus should be placed on local adaptations of foundation or keystone species, and that these local ecotypes should be moved within their own range. Hence, this type of relocation could be applied with minimal risk in many restoration efforts. We think that caution is needed when consid-ering the translocation of these foundation species, even within their range. Many recent studies have shown that foundation species can influence community structure and ecosystem processes through heritable traits, which sug-gests a genetic basis for ecosystem services. Thus, the translocation of different genotypes of foundation species might lead to unexpected results of colonization and might not be as "predictable" as Kreyling et al. have argued. Here, in our response, we stress how AC of foundation species can have important evolutionary consequences that might be impossible to reverse. We propose, whenever possible, (1) to favor population mixes of the foundation species to minimize the potential negative effects of spe-cific genotypes; and (2) to collect from adjacent popu-lations along ecological clines of the foundation species to mimic natural processes of migration under climate change.
La présence simultanée de chênes décidus et de chênes à feuilles persistantes est commune dans certaines régions au climat de type méditerranéen. néanmoins, on connaît peu de choses quant à un possible chevauchement des niches de régénération de ces espèces. nous avons étudié expérimentalement, les changements dans la survie, la croissance, la répartition de la biomasse, le contenu en azote des feuilles et l'efficacité de l'utilisation de l'eau (δ13C) chez de jeunes pousses d'un chêne décidu (Quercus cerrioides) et d'un chêne à feuilles persistantes (Quercus ilex) en réponse à des variations simultanées de la lumière et de la disponibilité en eau. les plantules de Q. cerrioides présentent des racines plus longues, une surface racinaire plus grande, des feuilles avec un contenu en azote plus élevé et un δ13C moins négatif ainsi que moins de feuilles que les plantules de Q. ilex. l'interaction entre les espèces et la lumière illustrée par la surface foliaire spécifique et par le rapport racine-tige fait ressortir l'existence d'un mécanisme propre à chacune des espèces pour faire face au stress hydrique. Chez Q. ilex, les feuilles sont plus coriaces alors que chez Q. cerrioides, le rapport racine-tige est plus important. les deux espèces présentent toutefois une survie et une croissance similaires dans la majeure partie du gradient de lumière et de disponibilité en eau. Ces résultats indiquent que les plantules des deux espèces réagissent de façon semblable aux variations de lumière et de disponibilité en eau, et ce malgré des ports de feuilles complètement différents. Ces performances similaires suggèrent l'existence d'une compétition entre les deux espèces pour certains microsites pendant leur établissement plutôt qu'un partage de la niche de régénération. Nomenclature: Castroviejo et al., 1986.
Assisted colonization as an adaptation strategy to conserve or restore biodiversity in the face of climate change deservedly evokes controversy. Assisted colonization is perceived by some as a last option for conserving endangered species and by others as a risky and unwise management effort due to current gaps of knowledge. Based on the pros and cons of the recent debate, we show that the current discussion mainly focuses on the assisted colonization of rare and endangered species beyond their natural range of distribution. We suggest that a more useful approach for the conservation of endangered species could occur by focusing on the relevant foundation or keystone species, which ensure ecosystem integrity for a multitude of dependent species by governing the habitat structure and micro-climate of the site. Examples of foundation species include dominant tree species in forests or dominant corals in coral reefs. For a given conservation or restoration need (e.g. conservation of rare species), we recommend the assisted colonization of pre-adapted ecotypes of the relevant foundation species from climates similar to future expectations for the target site. This approach could lead to climate-safe habitats for endangered species with minimal adverse effects on recipient ecosystems.
In southern France, the natural invasion by Quercus humilis of calcareous grassland takes place in a mosaic of herbaceous and scrubby patches. We hypothesized that the presence of the shrubs Buxus sempervirens and Juniperus communis alter the rate and the pathway of the succession by facilitating the regeneration of Q. humilis. To infer the process of facilitation at a large scale, the spatial distribution of Q. humilis was studied in relation to acorn sources and the type of plant cover in grazed and ungrazed sites.
Abundant recruitment up to 80 m from the wood margins and from isolated oak trees in grassland shows that acorns are dispersed effectively. At the three study sites, the density of Q. humilis individuals was higher under shrubs than in grassland, suggesting that facilitation may occur. This density difference was much higher in the grazed sites than in the ungrazed site. Moreover, before grazing by livestock, the distribution of first‐year seedlings is independent of vegetation cover. Thus, shrubs improve Q. humilis regeneration by protecting individuals from grazing. The high density of individuals at the northern edge of shrubs suggests that a second facilitation mechanism may exist, probably related to improved germination conditions. Facilitation by shrubs appears to be very important for Q. humilis dynamics.
Understanding the factors that determine the distributions of understory plants is important because they represent the largest component of temperate forest diversity. In the present study, we investigate the influence of topographic gradients and overstory structure on composition and abundance of understory shrub species in Massís de l’Orri (central Pyrenees, Lleida, Spain). We established 329 plots in two opposing hills in the massif at elevations ranging from 1500 to 2200 m, where we measured understory composition, overstory structure and physiographic features. Overall richness and diversity did not vary with aspect and showed only a small decrease with elevation. However, understory composition showed drastic changes related to elevation and aspect. Most species had differences between slopes, some of them showing higher cover in south-facing plots and the others in north-facing plots. Elevation also influenced percent cover of many understory shrub species, which showed either a decrease (Arctostaphylos uva-ursi, Rosa sp.), a maximum at intermediate values (Cytisus purgans) or an increase (Rhododendron ferrugineum) with elevation. The effect of the two variables was not independent, and percent cover of the different species depended on the overall effect of aspect and elevation. The species with highest occurrence in plots, Vaccinium myrtillus, increased with elevation in south-facing slopes but showed similar values in north-facing slopes. Compared to topographic variables, the effect of overstory variables on understory was considerably smaller. Understory species richness and diversity were inversely but weakly correlated with overstory cover but not with basal area. These overstory variables only affected negatively the presence of C. purgans and Juniperus communis, two shade-intolerant species that decrease their abundance when light decreases. Overall, the results obtained suggest that topographic variables have a stronger influence on understory composition than overstory structure in the study area, which is located in the southern distribution limit of temperate forests in Europe.
Lack of information on ecological characteristics of species across different continents hinders development of general world-scale quantitative vegetation dynamic models. We constructed common scales of shade, drought, and waterlogging tolerance for 806 North American, European/West Asian, and East Asian temperate shrubs and trees representing about 40% of the extant natural Northern Hemisphere species pool. These scales were used to test the hypotheses that shade tolerance is negatively related to drought and waterlogging tolerances, and that these correlations vary among continents and plant functional types. We observed significant negative correlations among shade and drought tolerance rankings for all data pooled, and separately for every continent and plant functional type, except for evergreen angiosperms. Another significant trade-off was found for drought and waterlogging tolerance for all continents, and for evergreen and deciduous angiosperms, but not for gymnosperms. For all data pooled, for Europe and East Asia, and for evergreen and deciduous angiosperms, shade tolerance was also negatively associated with waterlogging tolerance. Quantile regressions revealed that the negative relationship between shade and drought tolerance was significant for species growing in deep to moderate shade and that the negative relationship between shade and waterlogging tolerance was significant for species growing in moderate shade to high light, explaining why all relationships between different tolerances were negative according to general regression analyses. Phylogenetic signal in the tolerance to any one of the three environmental factors studied was significant but low, with only 21–24% of cladogram nodes exhibiting significant conservatism. The inverse relationships between different tolerances were significant in phylogenetically independent analyses both for the overall pool of species and for two multispecies genera (Pinus and Quercus) for which reliable molecular phylogenies were available. Only 2.6–10.3% of the species were relatively tolerant to two environmental stresses simultaneously (tolerance value !3), and only three species were tolerant to all three stresses, supporting the existence of functional trade-offs in adjusting to multiple environmental limitations. These trade-offs represent a constraint for niche differentiation, reducing the diversity of plant responses to the many combinations of irradiance and water supply that are found in natural ecosystems.
Quercus coccifera , a slow‐growing, evergreen oak, grows in contrasting environments in the Mediterranean Basin. Habitat‐based selection may have promoted divergence between populations with respect to phenotypic plasticity and genetic variability.
We tested the hypothesis that populations of the Q. coccifera originating from a rock outcrop, a continental garrigue formation and an oceanic forest would differ in their plastic response to light intensity. Plants from these populations were grown from acorns in a common garden at 100% and 20% full sunlight. Light response analysis was based on photochemical efficiency, xanthophyll pool, nutrient allocation, growth, crown architecture and light absorption.
Light‐responsive characters ranged from the subcellular to the whole‐plant level. The greatest divergences between sun and shade phenotypes were observed in leaf size, leaf angle and leaf area ratio. However, plasticity in these traits depended on plant provenance.
Regardless of the level of organization, populations were invariably ranked in the same order of plasticity when averaged over light‐responsive features, with plants originating from the rock outcrop showing the least plasticity and those from the forest the largest. The forest population also had the greatest genetic variability with respect to the isoperoxidase polymorphism.
Among populations, plants originating from the phosphorus‐deficient rock outcrop contained 30% more P per unit dry weight. Plants from the forest population had 5% more photoprotective xanthophylls, 30% larger total leaf area, with less lobed and larger leaves and a differential plasticity in leaf azimuth.
Differences among populations suggested ecotypic differentiation towards less phenotypic plasticity in the most homogeneous light environments. The ecological breadth of the species seemed to be derived not only from its tolerance of Mediterranean conditions but also from the specialization of its populations in contrasting habitats.
European Mediterranean landscapes have undergone changes in structure in recent years as a result of widespread agricultural land abandonment and cessation of silvicultural regimes. Studies concerning the regeneration dynamics of dominant forest species have become critical to the prediction of future landscape trends in these changing forest stands. Quercus ilex (holm oak) and Q. pubescens (downy oak) are considered to be the terminal point of secondary succession in extensive areas of the Mediterranean region. Recent studies, however, have suggested the existence of recruitment bottlenecks in oak genet populations as a result of current management regimes. In this study, we present evidence of the successful establishment of Q. ilex and Q. pubescens in Pinus halepensis (Aleppo pine) woodlands. We investigate the distribution patterns and spatial relationships among oak recruits and resident pines. Established P. halepensis is randomly distributed throughout the study area. Oak seedlings are positively associated with pine trees, suggesting that P. halepensis individuals provide safe sites for oak genet recruitment. We show that spatial patterns of recruitment are in agreement with the general model of spatial segregation described for other Mediterranean plant communities, with seeder species colonizing large openings after disturbance, followed by a more aggregated recruitment of resprouter species.
Aim To assess the spatial patterns of forest expansion (encroachment and densification) for mountain pine (Pinus uncinata Ram.) during the last 50 years at a whole mountain range scale by the study of different topographic and socio-economic potential drivers in the current context of global change.
Location The study area includes the whole distributional area of mountain pine in the Catalan Pyrenees (north-east Spain). This represents more than 80 municipalities, covering a total area of 6018 km2.
Methods Forest cover was obtained by image reclassification of more than 200 pairs of aerial photographs taken in 1956 and 2006. Encroachment and densification were determined according to changes in forest cover, and were expressed as binary variables on a 150 × 150 m cell-size grid. We then used logistic regression to analyse the effects of several topographic and socio-economic variables on forest expansion.
Results In the period analysed, mountain pine increased its surface coverage by 8898 ha (an increase of more than 16%). Mean canopy cover rose from 31.0% in 1956 to 55.6% in 2006. Most of the expansion was found on north-facing slopes and at low altitudes. Socio-economic factors arose as major factors in mountain pine expansion, as encroachment rates were higher in municipalities with greater population losses or weaker primary sector development.
Main conclusions The spatial patterns of mountain pine expansion showed a good match with the main patterns of land-use change in the Pyrenees, suggesting that land-use changes have played a more important role than climate in driving forest dynamics at a landscape scale over the period studied. Further studies on forest expansion at a regional scale should incorporate patterns of land-use changes to correctly interpret drivers of forest encroachment and densification.
Question: Will the predicted climate changes affect species distribution in the Iberian Peninsula?
Location: Iberian Peninsula (Spain and Portugal).
Methods: We modelled current and future tree distributions as a function of climate, using a computational framework that made use of one machine learning technique, the random forest (RF) algorithm. This algorithm provided good predictions of the current distribution of each species, as shown by the area under the corresponding receiver operating characteristics (ROC) curves. Species turnover, richness and the change in distributions over time to 2080 under four Intergovernmental panel on climate change (IPCC) scenarios were calculated using the species map outputs.
Results and Conclusions: The results show a notable reduction in the potential distribution of the studied species under all the IPCC scenarios, particularly so for mountain conifer species such as Pinus sylvestris, P. uncinata and Abies alba. Temperate species, especially Fagus sylvatica and Quercus petraea , were also predicted to suffer a reduction in their range; also sub‐mediterranean species, especially Q. pyrenaica , were predicted to undergo notable decline. In contrast, typically Mediterranean species appeared to be generally more capable of migration, and are therefore likely to be less affected.
Understanding seedling performance across resource gradients is crucial for defining the regeneration niche of plant species under current environmental conditions and for predicting potential changes under a global change scenario. A 2-year field experiment was conducted to determine how seedling survival and growth of two evergreen and two deciduous Quercus species vary along gradients of light and soil properties in two Mediterranean forests with contrasting soils and climatic conditions. Half the seedlings were subjected to an irrigation treatment during the first year to quantify the effects on performance of an alteration in the summer drought intensity. Linear and non-linear models were parameterized and compared to identify major resources controlling seedling performance. We found both site-specific and general patterns of regeneration. Strong site-specificity was found in the identity of the best predictors of seedling survival: survival decreased linearly with increasing light (i.e. increasing desiccation risk) in the drier site, whereas it decreased logistically with increasing spring soil water content (i.e. increasing waterlogging risk) in the wetter site. We found strong empirical support for multiple resource limitation at the drier site, the response to light being modulated by the availability of soil resources (water and P). Evidence for regeneration niche partitioning among Quercus species was only found at the wetter site. However, at both sites Quercus species shared the same response to summer drought alleviation through water addition: increased first-year survival but not final survival (i.e. after two years). This suggests that extremely dry summers (i.e. the second summer in the experiment) can cancel out the positive effects of previous wetter summers. Therefore, an increase in the intensity and frequency of summer drought with climate change might cause a double negative impact on Quercus regeneration, due to a general reduction in survival probability and the annulment of the positive effects of (infrequent) ‘wet’ years. Overall, results presented in this study are a major step towards the development of a mechanistic model of Mediterranean forest dynamics that incorporates the idiosyncrasies and generalities of tree regeneration in these systems, and that allow simulation and prediction of the ecological consequences of resource level alterations due to global change.
In this paper, I analyse the interaction between the holm-oak Quercus ilex, and one of its main dispersers, the European jay Garrulus glandarius, in an heterogeneous Mediterranean landscape. I quantify the spatial dispersal pattern of the seed shadow at two spatial scales, landscape (among patches) and microhabitat (within patches), by directly tracking the movement of seeds. Two main traits of the jay-mediated dispersal of holm-oak acorns across the landscape, the spatial pattern of dissemination and the distance from the source tree, are significantly and directly influenced by jay activity. Jays moved acorns nonrandomly, avoiding one main patch type of the study area to cache acorns, the shrubland-grasslands, and moving most of the acorns to pine stands, whether afforestation or open pinewoods. Within each patch type, jays had also a strong preference for caching acorns in some microhabitats, since>95% of the acorns dispersed by jays were cached beneath pines. The distance of holm-oak acorn dispersal was long in the study site, over 250 m, with some dispersals occurring up to 1 km from the source oaks. The shape of the dispersal kernel function fitted to the dispersal pattern produced by jays differed from those quantified for many other plant species. Jay-mediated dispersal had two components, one local and another produced by long-distance dispersal. Due to the heterogeneity of these Mediterranean environments, this difference in scale overlaps with a difference in habitat composition, short distances events resulting in dispersals within the same oak stands and long distance events resulting in dispersal outside of oak stands, usually to other vegetation units. Jay activity and movement pattern can have thus dramatic effects on both the local regeneration as well as the potential for regional spread of the holm-oak populations.