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Abstract

Mixed-severity disturbance regimes are prevalent in temperate forests worldwide, but key uncertainties remain regarding the variability of disturbance-mediated structural development pathways. This study investigates the influence of disturbance history on current structure in primary, unmanaged Norway spruce (Picea abies) forests throughout the Carpathian Mountains of central and eastern Europe, where windstorms and native bark beetle outbreaks are the dominant natural disturbances. We inventoried forest structure on 453 plots (0.1 ha) spanning a large geographical gradient (\>1,000 km), coring 15–25 canopy trees per plot for disturbance history reconstruction (tree core total n = 11,309). Our specific objectives were to: (1) classify sub-hectare-scale disturbance history based on disturbance timing and severity; (2) classify current forest structure based on tree size distributions (live, dead, standing, downed); (3) characterize structural development pathways as revealed by the association between disturbance history and current forest structural complexity. We used hierarchical cluster analysis for the first two objectives and indicator analysis for the third. The disturbance-based cluster analysis yielded six groups associated with three levels of disturbance severity (low, moderate, and high canopy loss) and two levels of timing (old, recent) over the past 200 years. The structure-based cluster analysis yielded three groups along a gradient of increasing structural complexity. A large majority of plots exhibited relatively high (53\%) or very high (26\%) structural complexity, indicated by abundant large live trees, standing and downed dead trees, and spruce regeneration. Consistent with conventional models of structural development, some disturbance history groups were associated with specific structural complexity groups, particularly low-severity/recent (very high complexity) and high-severity/recent (moderate complexity) disturbances. In other cases, however, the distribution of plots among disturbance history and structural complexity groups indicated either divergent or convergent pathways. For example, multiple disturbance history groups were significantly associated with the high complexity group, demonstrating structural convergence. These results illustrate that complex forest structure – including features nominally associated with old-growth – can be associated as much with disturbance severity as it is with conventional notions of forest age. Because wind and bark beetles are natural disturbance processes that can induce relatively high levels of tree mortality while simultaneously contributing to structural complexity and heterogeneity, we suggest that forest management plans allow for the stochastic occurrence of disturbance and variable post-disturbance development trajectories. Such applications are especially appropriate in conservation areas where biodiversity and forest resilience are management objectives, particularly given projections of increasing disturbance activity under global change.

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... Capercaillie requires specific habitat elements typical of mature and old-growth stages of forest development, such as semi-open forest habitats, presence of low-branched trees, high ground vegetation cover, snags, and uprooted trees (Bollmann et al., 2005;Mikoláš et al., 2017b). Those conditions are the result of forest development driven by natural disturbances, such as windthrow and bark beetle mortality, in unmanaged forests (Meigs et al., 2017). The species cannot shift to forests with different structures (but the same tree species composition) and sustain viable populations over the long term (Grimm and Storch, 2000). ...
... Commercial/classical forest management promotes stands that lack many of these critical structural-habitat elements that such specialists rely on (e.g., semi-open forest habitats, presence of lowbranched trees, high ground vegetation cover, snags, lying dead wood, old-habitat trees, and vertically complex canopies). Such complex forest structures are an inherent component of unmanaged forests that develop under a regime of natural mortality and disturbance processes (e.g., Meigs et al., 2017;Nagel et al., 2017). ...
... A high proportion of the forest biodiversity and habitats in Romania was arguably somewhat protected due to the former inaccessibility of many forests. Historically, it was difficult to access mountain areas and therefore no management or low-intensity management resulted in forests with structurally complex habitats in the remote regions of Romania (Meigs et al., 2017). Indeed, a large proportion of forests in the remote mountains was not necessarily untouched, but most have been developing without significant human interventions for decades and centuries. ...
Article
Amidst rapid global climate change and at a time when many adaptive policies and strategies have been implemented , reductionism in forest management decisions may have detrimental effects on forest biodiversity. Stăncioiu et al. (2018) made an important contribution by assessing forest connectivity based on tree species populations in Romania. Their study concluded that current management policies and inherited guidelines from the past likely promoted the conservation of regional biodiversity. In this viewpoint paper, we present a different perspective on their conclusion. We show that current management policies are threatening biodiversity in Romania, and changes in forest management policies are urgently needed to halt the loss of habitats of protected species. Although recent management policies likely did lead to good tree species connectivity, habitats of protected species are becoming increasingly fragmented by logging. Adopting policies to protect forest habitats of protected species, limiting large-scale salvage logging within protected areas, and restricting road building to reduce forest fragmentation are crucial steps towards the long-term persistence of biodiversity hotspots in the Romanian Carpathians.
... Our definition and conceptual framework of primary forests are consistent with relatively widely accepted criteria for European old-growth forests (Wirth et al., 2009;Burrascano, 2013;Knorn et al., 2013), namely unmanaged forests with natural stand composition, broad distribution of tree ages, high proportion of old canopy trees, diversity of horizontal and vertical structure, and a significant amount and diversity of standing and downed dead trees in different stages of decomposition. However, in addition to late-successional forests, we also considered all developmental phases, including early seral stages and young forests that originated after natural disturbances and natural regeneration, and without subsequent management, as with primary forest mosaics (Swanson et al., 2011;Svoboda et al., 2014;Meigs et al., 2017). The main criteria to decide about the inclusion of primary forests into the catalogue was the historical human impact detected by the forest stand maps, historical maps, and field inventory ( Table 1). ...
... In addition, uprooted trees or snags, whose biological age was considered to be the main cause of their breakage, could also be considered as veteran trees. As large standing and downed deadwood was also considered an important criterion, we used a threshold of having at least 10 pieces of large standing and downed dead wood per ha within the primary forests (Meigs et al., 2017). Based on the forest habitat type, large standing and downed deadwood was considered to have DBH ≥30 cm for forest habitats (such as Riparian and gallery woodlands, with dominant Alnus, Betula, Populus, or Salix, Mixed riparian floodplain and gallery woodlands, Pannonian Quercus pubescens woods, Nemoral bog conifer woodlands, Alnus swamp woods) and a DBH ≥50 cm, for all other forest habitats (see Table 2). ...
... This approach can create challenges when applying simple structural criteria across variable sites. For example, deadwood volume is highly variable among sites and developmental stages, for example due to differences in disturbance histories and their legacies, stand development rates and pathways (Meigs et al., 2017). In a spruce forest 100 years after a natural disturbance, deadwood that originated from the event later decomposed, but the stilt-rooted 'standing trees' indicated past regeneration on downed logs (Svoboda et al., 2010;Meyer et al., 2017). ...
Article
Given the global intensification of forest management and climate change, protecting and studying forests that develop free of direct human intervention-also known as primary forests-are becoming increasingly important. Yet, most countries still lack data regarding primary forest distribution. Previous studies have tested remote sensing approaches as a promising tool for identifying primary forests. However, their precision is highly dependent on data quality and resolution, which vary considerably. This has led to underestimation of primary forest abundance and distribution in some regions, such as the temperate zone of Europe. Field-based inventories of primary forests and methodologies to conduct these assessments are inconsistent; incomplete or inaccurate mapping increases the vulnerability of primary forest systems to continued loss from clearing and land-use change. We developed a comprehensive methodological approach for identifying primary forests, and tested it within one of Europe's hotspots of primary forest abundance: the Carpathian Mountains. From 2009 to 2015, we conducted the first national-scale primary forest census covering the entire 49,036 km 2 area of the Slovak Republic. We analyzed primary forest distribution patterns and the representativeness of potential vegetation types within primary forest remnants. We further evaluated the conservation status and extent of primary forest loss. Remaining primary forests are small, fragmented, and often do not represent the potential natural vegetation. We identified 261 primary forest localities. However, they represent only 0.47% of the total forested area, which is 0.21% of the country's land area. The spatial pattern of primary forests was clustered. Primary forests have tended to escape anthropogenic disturbance on sites with higher elevations, steeper slopes, rugged terrain, and greater distances from roads and settlements. Primary forest stands of montane mixed and subalpine spruce forests are more abundant compared to broadleaved forests. Notably, several habitat types are completely missing within primary forests (e.g., floodplain forests). More than 30% of the remaining primary forests are not strictly protected, and harvesting occurred at 32 primary forest localities within the study period. Almost all logging of primary forests was conducted inside of protected areas, underscoring the critical status of primary forest distribution in this part of Europe. Effective conservation strategies are urgently needed to stop the rapid loss and fragmentation of the remaining primary forests. Our approach based on precise, field-based surveys is widely applicable and transferrable to other fragmented forest landscapes.
... Natural disturbances represent key drivers in forest ecosystems dynamics Stephens et al., 2013;Seidl et al., 2014). For the Carpathian Norway spruce (Picea abies) forests, mixed-severity disturbance regimes have been identified as the dominant driver (Svoboda et al., 2014;Janda et al., 2017;Meigs et al., 2017;Schurman et al., 2018). The European bark beetle (Ips typographus) can be considered one of key factors determining the dynamics of European spruce-dominated forests (Temperli et al., 2013) and together with wind, are the major disturbance factors in the Carpathians . ...
... Fungal diversity is determined by site conditions, canopy closure, age structure, microclimatic conditions and importantly, by the amount and diversity (e.g. log size, decay stage, tree species) of deadwood (Heilmann-Clausen & Christensen, 2003;Seibold et al., 2016;Pouska et al., 2017;Hilmers et al., 2018;Tomao et al., 2020), all of which are significantly driven by natural disturbances (Meigs et al., 2017). Even relatively high volumes of deadwood are not able to guarantee high diversity of fungi (Hofmeister et al., 2015) unless there is sufficient variability in the size of deadwood, including large objects. ...
... Young forests with open canopy after a high-severity fire disturbance can be highly valuable for fungal biodiversity (Kouki & Salo, 2020) and some threatened forest specialists, such as Antrodiella citrinella, were more abundant in more open stands, recently disturbed by bark beetle, which agrees with findings of Bässler et al. (2012). However, the negative effects of canopy openness may be a transitional phase (temporary) since the dead wood in gaps will eventually become sheltered by the regeneration canopy during forest development (Meigs et al., 2017). In principle, a mosaic stand structure is largely driven by natural disturbances that generate higher structural heterogeneity, volumes of deadwood and light availability, which are all key factors influencing fungal communities . ...
Article
Understanding the processes shaping the composition of assemblages at multiple spatial scales in response to disturbance events is crucial for preventing ongoing biodiversity loss and for improving current forest management policies aimed at mitigating climate change and enhancing forest resilience. Deadwood-inhabiting fungi represent an essential component of forest ecosystems through their association with deadwood decomposition and the cycling of nutrients and carbon. Although we have sufficient evidence for the fundamental role of deadwood availability and variability of decay stages for fungal species diversity, the influence of long-term natural disturbance regimes as the main driver of deadwood quantity and quality has not been sufficiently documented. We used a dendroecological approach to analyse the effect of 250-years of historical natural disturbance and structural habitat elements on local (plot-level) and regional (stand-level) species richness of deadwood-inhabiting fungi. We used data collected from 51 study plots within nine best-preserved primary spruce forest stands distributed across the Western Carpathian Mountains. Historical disturbances shaped the contemporary local and regional species richness of fungi, with contrasting impacts of disturbance regime components at different spatial scales. While local diversity of red-listed species has increased due to higher disturbance frequency, regional diversity of all species has decreased due to higher severity historical disturbances. The volume of deadwood positively influenced the species richness of deadwood-inhabiting fungi while canopy openness had a negative impact. The high number of observed rare species highlights the important role of primary forests for biodiversity conservation. From a landscape perspective, we can conclude that the distribution of species from the regional species pool is-at least to some extent-driven by past spatiotemporal patterns of disturbance events. Natural disturbances occurring at higher frequencies that create a mosaic forest structure are necessary for fungal species-especially for rare and endangered taxa. Thus, both the protection of intact forest landscapes and forest management practises that emulate natural disturbance processes are recommended to support habitats of diverse fungal communities and their associated ecosystem functions.
... Studies have increasingly highlighted the differences in diversity among stands of old-growth forests in terms of structure and composition, even within a relatively restricted landscape; this view of old-growth forests contrasts with the idea of these stands as being homogeneous (Fenton & Bergeron, 2011;Martin et al., 2018;Meigs et al., 2017). Variations in the nature, severity, and recurrence of secondary disturbances play a major role in forming these complex matrices Portier et al., 2018;Svoboda et al., 2014). ...
... Variations in the nature, severity, and recurrence of secondary disturbances play a major role in forming these complex matrices Portier et al., 2018;Svoboda et al., 2014). In particular, recent emphasis has been placed on the importance of moderate-severity disturbances, also known as intermediate-severity disturbances, on the dynamics of these ecosystems (Kuuluvainen et al., 2014;Martin et al., 2019;Meigs et al., 2017). Moderate-severity disturbances are defined as disturbances that exceeds the gap scale (death of one tree or a small group of trees) without being catastrophic (Hart & Kleinman, 2018). ...
... In some cases, recurrent and severe secondary disturbances may override stand resistance, thereby reinitiating forest succession (De Grandpré et al., 2018;Donato et al., 2012;Meigs et al., 2017). ...
... Studies have increasingly highlighted the differences in diversity among stands of old-growth forests in terms of structure and composition, even within a relatively restricted landscape; this view of old-growth forests contrasts with the idea of these stands as being homogeneous (Fenton & Bergeron, 2011;Martin et al., 2018;Meigs et al., 2017). Variations in the nature, severity, and recurrence of secondary disturbances play a major role in forming these complex matrices Portier et al., 2018;Svoboda et al., 2014). ...
... Variations in the nature, severity, and recurrence of secondary disturbances play a major role in forming these complex matrices Portier et al., 2018;Svoboda et al., 2014). In particular, recent emphasis has been placed on the importance of moderate-severity disturbances, also known as intermediate-severity disturbances, on the dynamics of these ecosystems (Kuuluvainen et al., 2014;Martin et al., 2019;Meigs et al., 2017). Moderate-severity disturbances are defined as disturbances that exceeds the gap scale (death of one tree or a small group of trees) without being catastrophic (Hart & Kleinman, 2018). ...
... In some cases, recurrent and severe secondary disturbances may override stand resistance, thereby reinitiating forest succession (De Grandpré et al., 2018;Donato et al., 2012;Meigs et al., 2017). ...
Article
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en In boreal landscapes, emphasis is currently placed on close‐to‐nature management strategies, which aim to maintain the biodiversity and ecosystem services related to old‐growth forests. The success of these strategies, however, depends on an accurate understanding of the dynamics within these forests. While moderate‐severity disturbances have recently been recognized as important drivers of boreal forests, little is known about their effects on stand structure and growth. This study therefore aimed to reconstruct the disturbance and postdisturbance dynamics in boreal old‐growth forests that are driven by recurrent moderate‐severity disturbances. We studied eight primary old‐growth forests in Québec, Canada, that have recorded recurrent and moderately severe spruce budworm (Choristoneura fumiferana [Clem.]) outbreaks over the 20th century. We applied an innovative dendrochronological approach based on the combined study of growth patterns and releases to reconstruct stand disturbance and postdisturbance dynamics. We identified nine growth patterns; they represented trees differing in age, size, and canopy layer. These patterns highlighted the ability of suppressed trees to rapidly fill gaps created by moderate‐severity disturbances through a single and significant increase in radial growth and height. Trees that are unable to attain the canopy following the disturbance tend to remain in the lower canopy layers, even if subsequent disturbances create new gaps. This combination of a low stand height typical of boreal forests, periodic disturbances, and rapid canopy closure often resulted in stands constituted mainly of dominant and codominant trees, similar to even‐aged forests. Overall, this study underscored the resistance of boreal old‐growth forests owing to their capacity to withstand repeated moderate‐severity disturbances. Moreover, the combined study of growth patterns and growth release demonstrated the efficacy of such an approach for improving the understanding of the fine‐scale dynamics of natural forests. The results of this research will thus help develop silvicultural practices that approximate the moderate‐severity disturbance dynamics observed in primary and old‐growth boreal forests. Résumé fr Dans les paysages boréaux, l'accent est désormais mis sur des stratégies de gestion proches de la nature afin de maintenir la biodiversité et les services écosystémiques liés aux vieilles forêts. Le succès de ces stratégies dépend toutefois d'une compréhension fine de la dynamique de ces forêts. Les perturbations de sévérité modérée ont ainsi été récemment reconnues comme étant d’importants moteurs de la dynamique des forêts boréales, mais l’on sait encore peu de choses de leur influence sur la structure et la croissance des peuplements. Par conséquent, l'objectif de cette étude est de reconstruire les dynamiques de perturbation et post‐perturbation dans les vieilles forêts boréales causées par des perturbations récurrentes de sévérité modérée. Nous avons étudié huit vieilles forêts primaires au Québec, Canada, ayant enregistré des épidémies de tordeuse des bourgeons de l'épinette (Choristoneura fumiferana [Clem.]) récurrentes et de sévérité modérée au cours du 20ème siècle. Nous avons utilisé une approche dendrochronologique innovante combinant l’étude des patrons et des reprises de croissance pour reconstruire la dynamique de perturbation et post‐perturbation de ces forêts. Nous avons identifié neuf patrons de croissance, observés dans des arbres d'âge, de taille ou de strate de canopée différents, indiquant des dynamiques particulières. Ces patrons ont mis en évidence la capacité des arbres opprimés à rapidement combler les trouées dans la canopée en un unique et significatif accroissement de circonférence et de hauteur. En revanche, les arbres déjà situés dans la canopée ont eu peu d'influence sur la fermeture de ces trouées. En conséquence, les arbres dominants et codominants étaient les plus fréquents dans la canopée. Les résultats de cette étude soulignent la résistance des vieilles forêts boréales aux perturbations récurrentes et de sévérité modérée, car les arbres du sous‐étage peuvent rapidement combler les trouées qui en résultent. Cependant, les arbres incapables d’atteindre le sommet de la canopée à la suite d’une perturbation resteront ensuite souvent dans les strates inférieures de la canopée, même si des perturbations subséquentes créent ensuite de nouvelles trouées. La combinaison de la faible hauteur des arbres typique des forêts boréales, des perturbations périodiques et de la rapide fermeture des trouées forme des peuplements avec une structure verticale ressemblant à celle des forêts équiennes. Globalement, cette étude souligne la résistance des vieilles forêts boréales en raison de leur capacité à supporter des perturbations répétées de sévérité modérée. De plus, l’étude combinée des patrons et des reprises de croissance démontre l’efficacité de cette approche pour reconstruire la dynamique à échelle fine des forêts naturelles. Les résultats de cette recherche contribueront ainsi à développer des pratiques sylvicoles analogues à la dynamique de perturbation de sévérité modérée observée dans les vieilles forêts primaires des paysages boréaux.
... In recent years, however, several authors have highlighted the limitations of the commonly accepted vision of old-growth forests. Indeed, this single term frequently lumps together a diversity of forests with different structures, dynamics, habitats and histories, even within the same territory (Halpin and Lorimer, 2016;Martin et al., 2021a;Meigs et al., 2017). The transition to the old-growth stage is a gradual process, where the pioneer species that appeared following the last primary disturbance (i.e., disturbance of high severity that reinitiates forest succession) disappear progressively, while the structure becomes increasingly more complex (Franklin et al., 2002;Wirth et al., 2009). ...
... The transition to the old-growth stage is a gradual process, where the pioneer species that appeared following the last primary disturbance (i.e., disturbance of high severity that reinitiates forest succession) disappear progressively, while the structure becomes increasingly more complex (Franklin et al., 2002;Wirth et al., 2009). Old-growth forest stands where the pioneer cohort has disappeared can be distinguished by their secondary disturbance history, given that the latter strongly influences forest structure and habitats (Kozák et al., 2020;Martin et al., 2021a;Meigs et al., 2017). Therefore, it is not only necessary to identify oldgrowth forests accurately but also to distinguish the different structures and composition that they can assume to ensure their sustainable management. ...
... Old-growth forests are ecosystems of high-complexityincluding those in boreal landscapesand can take many forms (Martin et al., 2018;Meigs et al., 2017;Pesklevits et al., 2011). Similarly, tiles that were inaccurately classified generally presented intermediate values for the studied indices compared to those accurately classified, and were close to those of the undisturbed old-growth/accurate pair (Fig. 5). ...
Article
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In old-growth forests, natural disturbances form a complex mosaic of structures, providing a wide diversity of habitats and functions of great importance. Old-growth forests are still often seen as a homogeneous whole and few remote-sensing approaches have been tested to identify their structural diversity, especially in boreal forests. The aim of this study is to use a combination of airborne LiDAR and satellite imagery to identify and discriminate old-growth forest structures resulting from different disturbance histories. The study area, which was located in the mixed boreal forest of Quebec (Canada), is Monts Valin National Park and adjacent managed territories. Balsam fir (Abies balsamea (L.) Mill) is the dominant species in the study area, but hardwood species such as white birch (Betula papyrifera Marsh.) and trembling aspen (Populus tremuloides Michx.) can also be abundant in the early succession stages. Four forest classes were studied: second-growth (logged between 1970 and 1980); transition old-growth (burned in 1920); undisturbed old-growth (unburned for at least 125 years); and disturbed old-growth forest (unburned for at least 125 years, but severely disturbed by an insect outbreak around 1980). A multivariate Random Forest model was used to discriminate the classes on 6466 1 ha tiles, based on 11 complementary LiDAR and satellite-derived indices describing stand vertical and horizontal structure, together with "greenness" and disturbance history over the last 30 years. This model had high predictive efficiency (AUC = 94.2), with 81.8% of the tiles accurately classified. Interestingly, undisturbed old-growth forests exhibited intermediate characteristics compared to transition and disturbed old-growth forests. This emphasizes that some structural attributes recognized as important for the classification of temperate and tropical old-growth forests, such as high vertical complexity, are of lesser relevance for boreal old-growth forests. In comparison to undisturbed old-growth forests, transition old-growth forests had a taller canopy of high "greenness" due to a greater hardwood abundance; disturbed old-growth forests had a higher gap fraction and heterogeneity in tree size; second-growth forests exhibited a lower and more even canopy. Misclassified tiles were explained by spatial variation in disturbance severity or different levels of forest resistance and resilience to disturbance. These misclassifications are also of ecological interest, as they highlight the nuances in structural diversity that are rarely identified by disturbance mapping. A reasonable combination of LiDAR and satellite indices was effective not only in discriminating old-growth forests from second-growth forests, but also identifying their different structures, which result from specific disturbance histories. This method could contribute to effective monitoring of changes in the areas and characteristics old-growth forest that are caused by anthropogenic and natural disturbances.
... 27%) [25]. Primary forests are the result of complex natural disturbance histories, and are typically highly heterogeneous, both within and among stands that include the range in seral stages as well as old-growth forest [26,27]. Their structural heterogeneity translates into high spatial variability in carbon storage and biodiversity, although primary forests generally maintain high levels of both [28]. ...
... pathways, or they may be attributable to Kortmann et al. [60] only investigating dynamics over two decades following disturbance, a limited timeframe that could correspond to shortterm post-disturbance reproductive success. The preference of capercaillies to moderately disturbed plots independently of disturbance timing as found here may also be explained by the fact that moderate severity disturbances-both recent and further in the past-generally lead to high structural complexity in the studied primary forests [26]. In general, moderate severity disturbance could result in an optimal balance, under which several forest functions can reach relatively high levels (see the overlaps in figure 2). ...
... In particular, they emphasize that accounting for long-term variation of past disturbance could improve current policies aimed at mitigating climate change and biodiversity loss. Disturbances have long-lasting effects on forest functions and post-disturbance successional pathways [26]. Clearly, accounting for long time scales and alternative post-disturbance development trajectories poses a significant challenge to designing effective conservation and mitigation strategies, particularly given projected changes in disturbance regimes. ...
Article
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With accelerating environmental change, understanding forest disturbance impacts on trade-offs between biodiversity and carbon dynamics is of high socioeconomic importance. Most studies, however, have assessed immediate or short-term effects of disturbance, while long-term impacts remain poorly understood. Using a tree-ring-based approach, we analysed the effect of 250 years of disturbances on present-day biodiversity indicators and carbon dynamics in primary forests. Disturbance legacies spanning centuries shaped contemporary forest co-benefits and trade-offs, with contrasting, local-scale effects. Disturbances enhanced carbon sequestration, reaching maximum rates within a comparatively narrow post-disturbance window (up to 50 years). Concurrently, disturbance diminished aboveground carbon storage, which gradually returned to peak levels over centuries. Temporal patterns in biodiversity potential were bimodal; the first maximum coincided with the short-term post-disturbance carbon sequestration peak, and the second occurred during periods of maximum carbon storage in complex old-growth forest. Despite fluctuating local-scale trade-offs, forest biodiversity and carbon storage remained stable across the broader study region, and our data support a positive relationship between carbon stocks and biodiversity potential. These findings underscore the interdependencies of forest processes, and highlight the necessity of large-scale conservation programmes to effectively promote both biodiversity and long-term carbon storage, particularly given the accelerating global biodiversity and climate crises.
... Second, because disturbance changes the structure of the forest, these variables can be interpreted as a rough proxy for forest structural complexity. Forests with lower severity disturbance and disturbance that happened further in the past are more likely to display higher structural complexity (Janda et al., 2017;Meigs et al., 2017). Thus, we are examining the direct effect of past disturbance on future disturbance as well as approximating an indirect effect of structure on disturbance susceptibility. ...
... Disturbance from small-scale convective storms may have only affected one plot or a few trees and could be averaged out when calculating the disturbance severity at the stand scale. However, small-scale disturbance dynamics such as those created by small-scale convective storms cannot be ignored as they create forests of high structural complexity by opening up gaps in which recruitment can diversify the age and size profile of the forest (Franklin et al., 2002;Lorimer & Halpin, 2014;Meigs et al., 2017;Tepley et al., 2013). These localized events increase forest horizontal and vertical heterogeneity by creating gaps for seedling/sapling recruitment. ...
... The fact that cyclone-induced windstorms are driving disturbance dynamics at stand scales has implications for stand structure. Large severe disturbances can reduce local structural complexity (Janda et al., 2017;Meigs et al., 2017), however, even the most severe stand level disturbance observed here would only be classified as low or possibly moderate severity in the global/European context (see predicted disturbance severities around 0.15 proportion canopy area removed in Figure 4). So, even the stand scale disturbances observed here are still increasing structural complexity of stands through gap creation and patch dynamics, only the gap sizes are likely a bit larger than those produced through convective instability. ...
Article
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Wind is the leading disturbance agent in European forests, and the magnitude of wind impacts on forest mortality has increased over recent decades. However, the atmospheric triggers behind severe winds in Western Europe (large‐scale cyclones) differ from those in Southeastern Europe (small‐scale convective instability). This geographic difference in wind drivers alters the spatial scale of resulting disturbances and potentially the sensitivity to climate change. Over the 20th century, the severity and prevalence of cyclone‐induced windstorms have increased while the prevalence of atmospheric instability has decreased and thus, the trajectory of Europe‐wide windthrow remains uncertain. To better predict forest sensitivity and trends of windthrow disturbance we used dendrochronological methods to reconstruct 140 years of disturbance history in beech‐dominated primary forests of Central and Eastern Europe. We compared generalized linear mixed models of these disturbance time series to determine whether large‐scale cyclones or small‐scale convective storms were more responsible for disturbance severity while also accounting for topography and stand character variables likely to influence windthrow susceptibility. More exposed forests, forests with a longer absence of disturbance, and forests lacking recent high severity disturbance showed increased sensitivity to both wind drivers. Large‐scale cyclone‐induced windstorms were the main driver of disturbance severity at both the plot and stand scale (0.1–∼100 ha) whereas convective instability effects were more localized (0.1 ha). Though the prevalence and severity of cyclone‐induced windstorms have increased over the 20 century, primary beech forests did not display an increase in the severity of windthrow observed over the same period.
... Radial growth patterns of increment cores were analyzed for evidence of past disturbance events within each plot. Quantitative reconstructions of disturbance histories for different regions of the larger data set used here have been published previously (Standovár & Kenderes, 2003;Svoboda et al., 2014;Trotsiuk et al., 2014;Janda et al., 2017;Meigs et al., 2017;Nagel et al., 2017;Schurman et al., 2018;Janda et al., 2019;Schurman, Babst, Björklund, et al., 2019;Čada et al., 2020;Frankovič et al., 2020), and provide detailed descriptions of dendroecological methods. We therefore only briefly summarize the methods used to reconstruct disturbance below. ...
... Disturbance history reconstruction and lifetime growth patterns of trees were used to derive several variables that may influence longevity. These included the timing and severity (i.e., percent plot canopy area killed) of the reconstructed maximum severity disturbance event on each plot (Meigs et al., 2017) (hereafter referred to as disturbance severity and disturbance year), as well as the number of release events per core. To assess the influence of growth rates on longevity, we used the average growth rate of the first 50 years following Bigler (2016) (hereafter referred to as early growth). ...
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Aims We examined differences in lifespan among the dominant tree species (spruce (Picea abies (L.) H. Karst.), fir (Abies alba Mill.), beech (Fagus sylvatica L.), and maple (Acer pseudoplatanus L.)) across primary mountain forests of Europe. We ask how disturbance history, lifetime growth patterns, and environmental factors influence lifespan. Locations Balkan mountains, Carpathian mountains, Dinaric mountains. Methods Annual ring widths from 20,600 cores from primary forests were used to estimate tree life spans, growth trends, and disturbance history metrics. Mixed models were used to examine species-specific differences in lifespan (i.e. defined as species-specific 90th percentiles of age distributions), and how metrics of radial growth, disturbance parameters, and selected environmental factors influence lifespan. Results While only a few beech trees surpassed 500 years, individuals of all four species were older than 400 years. There were significant differences in lifespan among the four species (beech > fir > spruce > maple), indicating life history differentiation in lifespan. Trees were less likely to reach old age in areas affected by more severe disturbance events, whereas individuals that experienced periods of slow growth and multiple episodes of suppression and release were more likely to reach old age. Aside from a weak but significant negative effect of vegetation season temperature on fir and maple lifespan, no other environmental factors included in the analysis influenced lifespan. Conclusions Our results indicate species-specific biological differences in lifespan, which may play a role in facilitating tree species coexistence in mixed temperate forests. Finally, natural disturbances regimes were a key driver of lifespan, which could have implications for forest dynamics if regimes shift under global change.
... In this view, shifts from density dependent to density independent mortality, caused for example by fine-scale canopy disturbances, are expected to only occur late in stand development, leading to similar forest structures before old-growth conditions develop. However, some studies have explored alternate developmental pathways that can lead to distinct differences in forest structure earlier in stand development, for example in boreal conifer forests of Canada (Harper et al., 2005;Lecomte et al., 2006;Martin et al., 2018), and in temperate western coniferous forests (Donato et al., 2012;Reilly et al., 2015), European spruce forests (Meigs et al., 2017), as well as hardwood dominated systems of the Upper Midwest (Lorimer and Halpin, 2014) (see Table S1 for more examples). Moreover, recent evidence suggests that a broader range of disturbance frequencies, severities and sizes affect forests in the northern hardwood region than recognized in earlier studies (Foster et al., 1998;Frelich and Reich, 1995;Frelich and Lorimer, 1991;Hardiman et al., 2011;North and Keeton, 2008;Seymour et al., 2002). ...
... These disturbances are caused by wind events of variable severity, including microbursts (Hanson and Lorimer, 2007;Meigs and Keeton, 2018), fire (Schulte and Mladenoff, 2005), insects (Chen et al., 2017), disease (Cale and McNulty, 2018), and ice storms (Millward and Kraft, 2004). Partial and mixed-severity disturbances can induce multiple development pathways and thus alter forest structure under comparable environmental conditions (Donato et al., 2012;Meigs et al., 2017). They can even accelerate structural development towards oldgrowth conditions in some cases (Abrams and Scott, 1989;Meigs and Keeton, 2018), for instance, by creating a heterogeneous vertical canopy structure (Keeton and Franklin, 2005) and increasing the amount of standing and lying deadwood (Keeton, 2006). ...
Article
Elements of forest structure are fundamentally associated with an array of ecosystem services and habitat characteristics. However, forest structure varies, in particular, through interactions with natural and human disturbances. Both variation in structural characteristics and associated relationships with ecosystem service outcomes have been poorly explored in mature, secondary forests redeveloped since 19th century agricultural abandonment in the eastern United States. Our study addressed this uncertainty focusing on carbon storage as an important climate regulation service. We conducted an inventory of 45 plots sharing similar land use history (i) to identify differences in forest structure, and (ii) to investigate links between stand structure and aboveground carbon storage. We derived 19 structural attributes and used these in Agglomerative Hierarchical Clustering (AHC) to categorize structurally different groups. Subsequently, we analyzed carbon density in each cluster and employed a random forest algorithm to derive partial effects of structural attributes on carbon storage. We found a distinctive disparity in forest structure inferred from two hardwood-dominated and one softwood-dominated clusters. Nine variables (cavity tree density, conifer ratio, foliage height index, gap area, live basal area, species diversity, variation in heights and diameters, and vertical shrub cover) explained significant differences between these clusters. Carbon storage varied markedly, and was highest in the softwood cluster. Structural complexity was overall positively associated with carbon storage, whereas this effect was more distinctive in hardwood compared to softwood-dominated forests. In particular, five variables exhibited a positive (conifer ratio, diameter variation, dead basal area, large live trees, and live basal area), one a negative (live tree density), and two (dead tree density and species diversity) a mixed relationship with carbon storage. Despite only moderate variation in climatic conditions across the investigated plots, we found a strong sensitivity of carbon storage to mean annual temperature. In contrast, annual precipitation and topography had no effect on carbon storage. The link between structural complexity and carbon storage suggests a high potential to actively increase forest carbon density. Based on our findings, a variety of options are available to enhance forest structure, and thus to improve carbon storage in managed forest ecosystems. These include, for instance, increasing the variability in tree dimensions and fostering large live trees which may improve niche complementarity. Increasing structural complexity in managed forest stands may thus improve buffering of potentially negative impacts of climate change on carbon stocks.
... Heterogeneity can dampen the cross-scale interactions and amplifying feedbacks that are necessary for catastrophic events and regime shifts (Peters et al. 2004). Specifically, variability in recovery can have long-lasting effects on the development of forest ecosystems (Meigs et al. 2017), and can decrease the vulnerability of forests to future disturbances by preventing synchronous exceedance of susceptibility thresholds for, e.g., bark beetle outbreaks (Seidl et al. 2016a). Hence, not only the temporal signal of recovery (i.e., recovery rate) but also its spatial pattern (i.e., variability in recovery) needs to be considered for a comprehensive quantification of forest ecosystem resilience to disturbance (Scheffer et al. 2015;Braziunas et al. 2018). ...
... We found slightly higher structural variability in unmanaged forests, especially [ 25 years post-disturbance. This finding is well in line with theoretical considerations suggesting that initial variability in recovery and pre-disturbance structural legacies lead to high structural diversity already in early stages of forest development (Donato et al. 2012;Bace et al. 2015), which can persist throughout stand development Meigs et al. 2017). Especially the higher variability in stand heights for beech-dominated forests suggests the development of a more diverse canopy structure in unmanaged forests compared to managed forests. ...
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Context Recovery from disturbances is a prominent measure of forest ecosystem resilience, with swift recovery indicating resilient systems. The forest ecosystems of Central Europe have recently been affected by unprecedented levels of natural disturbance, yet our understanding of their ability to recover from disturbances is still limited. Objectives We here integrated satellite and airborne Lidar data to (i) quantify multi-decadal post-disturbance recovery of two indicators of forest structure, and (ii) compare the recovery trajectories of forest structure among managed and un-managed forests. Methods We developed satellite-based models predicting Lidar-derived estimates of tree cover and stand height at 30 m grain across a 3100 km² landscape in the Bohemian Forest Ecosystem (Central Europe). We summarized the percentage of disturbed area that recovered to > 40% tree cover and > 5 m stand height and quantified the variability in both indicators over a 30-year period. The analyses were stratified by three management regimes (managed, protected, strictly protected) and two forest types (beech-dominated, spruce-dominated). Results We found that on average 84% of the disturbed area met our recovery threshold 30 years post-disturbance. The rate of recovery was slower in un-managed compared to managed forests. Variability in tree cover was more persistent over time in un-managed forests, while managed forests strongly converged after a few decades post-disturbance. Conclusion We conclude that current management facilitates the recovery of forest structure in Central European forest ecosystems. However, our results underline that forests recovered well from disturbances also in the absence of human intervention. Our analysis highlights the high resilience of Central European forest ecosystems to recent disturbances.
... The ability to easily and effectively identify the diversity of old-growth forest types is an important issue and not only for the boreal biomes. Several recent studies in temperate and alpine forests underline the complexity of stand structural changes under natural disturbance regimes, including when the old-growth stage is reached (Lorimer and Halpin 2014;Reilly et al. 2015;Meigs et al. 2017). In this context, the efficacy of large-scale aerial surveys should be evaluated in all territories that are facing or have faced significant erosion of natural or near-natural landscapes due to industrial-scale forest management. ...
... However, the risk of misclassifying old-growth forests because of inaccurate thresholds or indicators not only concerns Canada but also applies to all countries using large-scale aerial inventories. Old-growth forests seem to be defined by high structural diversity, independent of biome, resulting in a high diversity of old-growth forest "types" (e.g., Lorimer and Halpin 2014;Reilly et al. 2015;Meigs et al. 2017). A better recognition of the diversity of oldgrowth forests within the same territory is therefore a necessary step to ensure the development of reliable large-scale inventories. ...
Article
The erosion of old-growth forests in boreal managed landscapes is a major issue currently faced by forest managers; however, resolving this problem requires accurate surveys. The intention of our study was to determine if historic operational aerial forest surveys accurately identified boreal old-growth forests in Quebec, Canada. We first compared stand successional stages (even-aged vs. old-growth) in two aerial surveys performed in 1968 (preindustrial aerial survey) and 2007 (modern aerial survey) on the same 2200 km ² territory. Second, we evaluated the accuracy of the modern aerial survey by comparing its results with those of 74 field plots sampled in the study territory between 2014 and 2016. The two aerial surveys differed significantly; 80.8% of the undisturbed stands that were identified as “old-growth” in the preindustrial survey were classified as “even-aged” in the modern survey, and 60% of the stands identified as “old-growth” by field sampling were also erroneously identified as “even-aged” by the modern aerial survey. The scarcity of obvious old-growth attributes in boreal old-growth forests, as well as poorly adapted modern aerial survey criteria (i.e., criteria requiring high vertical stratification and significant changes in tree species composition along forest succession), were the main factors explaining these errors. It is therefore likely that most of Quebec’s boreal old-growth forests are currently not recognized as such in forest inventories, challenging the efficacy of sustainable forest management policies.
... Second, once the true old-growth stage is reached, each stand may be driven by a particular secondary disturbance regime, mixing low-and moderate-severity disturbances at different proportions and producing the structural diversity observed by Martin et al. (2018). Third, disturbances of moderate severity can create young forest structures that are neither evenaged nor old growth (Donato et al. 2012;Meigs et al. 2017;Hart and Kleinman 2018). Donato et al. (2012) qualified these stands as "born-complex" forests, i.e., young stands exhibiting a structural complexity usually attributed to old-growth forests. ...
... In addition, such complex disturbance histories are evidence of both the strong resistance and resilience of boreal old-growth forests. Yet, recent studies have emphasized how moderateseverity disturbances can, in some cases, rejuvenate mature and old-growth stands (Donato et al. 2012;Meigs et al. 2017). Therefore, managing old-growth boreal forests requires caution and a thorough knowledge of stand characteristics to ensure their sustainable management. ...
Article
Key message Both low- and moderate-severity secondary disturbances are drivers of eastern Canadian boreal old-growth forests dynamics. Moderate-severity disturbances reflect mainly spruce budworm outbreaks. Low-severity disturbances are produced by both spruce budworm outbreaks and random events such as windthrow. Each level of disturbance severity has a specific impact on stand dynamics, and both shape the diversity of boreal old-growth forests. ContextA regular succession of low-severity disturbances is seen as determining the dynamics of the old-growth stage (gap dynamics); however, recent studies suggest that moderate-severity secondary disturbances also play an important role in the dynamics of eastern Canadian boreal forests.AimsThis study aims to determine if eastern Canadian boreal old-growth forests are driven by a combination of low- and moderate-severity secondary disturbances.Methods We reconstructed the 200-year disturbance history of 20 boreal old-growth stands using dendrochronological analysis. We discriminated low- from moderate-severity disturbances based on their respective influence on mean stand growth.ResultsThe secondary disturbance regime of eastern Canadian boreal old-growth forests varies highly over time, reflected by disturbance peaks in the chronological record. Most peaks occurred during spruce budworm outbreaks related to both low- and moderate-severity disturbances. Between each peak, low-severity disturbances dominate. Each level of disturbance severity has specific consequences for stand dynamics.Conclusion Both low and moderate secondary disturbances are drivers of forest dynamics in eastern Canadian boreal old-growth stands and shape the structural diversity of these stands. The complexity of these dynamics should be recognized in management planning to ensure the efficiency of old-growth forest conservation policies.
... remnant live trees, standing and downed woody debris, advanced tree regeneration not affected by disturbance, heterogeneous seed bank) and their influence on post-disturbance forest development (Diskin, Rocca, Nelson, Aoki, & Romme, 2011;Johnstone et al., 2016;Kayes & Tinker, 2012;Seidl, Rammer, & Spies, 2014). This complexity can result in multiple successional pathways (Meigs et al., 2017;Tepley, Swanson, & Spies, 2013) creating diversity on the landscape, which, in turn, dampens future forest susceptibility to spreading disturbances, such as bark beetles (Hart, Veblen, Mietkiewicz, & Kulakowski, 2015;Honkaniemi, Rammer, & Seidl, 2020;Seidl, Donato, Raffa, & Turner, 2016). Empirical findings and simulation studies from North America suggest that past bark beetle forest structures with climatic conditions favourable for bark beetle outbreaks. ...
... We expected compositional diversity to increase due to disturbances creating niches for the establishment of new tree species, and due to reduction in the competitive strength of spruce (Hilmers et al., 2019;Thom et al., 2017a). Furthermore, we expected forest structure to increase in diversity due to the effect of disturbance legacies as well as spatially heterogeneous regeneration and stand development (Donato et al., 2012;Meigs et al., 2017). ...
Article
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Bark beetle outbreaks have intensified in many forests around the globe in recent years. Yet, the legacy of these disturbances for future forest development remains unclear. Bark beetle disturbances are expected to increase further because of climate change. Consequently, feedbacks within the disturbance regime are of growing interest, for example, whether bark beetle outbreaks are amplifying future bark beetle activity (through the initiation of an even‐aged cohort of trees) or dampening it (through increased structural and compositional diversity). We studied bark beetle–vegetation–climate interactions in the Bavarian Forest National Park (Germany), an area characterised by unprecedented bark beetle activity in the recent past. We simulated the effect of future bark beetle outbreaks on forest structure and composition and analysed how disturbance‐mediated forest dynamics influence future bark beetle activity under different scenarios of climate change. We used process‐based simulation modelling in combination with machine learning to disentangle the long‐term interactions between vegetation, climate and bark beetles at the landscape scale. Disturbances by the European spruce bark beetle were strongly amplified by climate change, increasing between 59% and 221% compared to reference climate. Bark beetle outbreaks reduced the dominance of Norway spruce (Picea abies (L.) Karst.) on the landscape, increasing compositional diversity. Disturbances decreased structural diversity within stands (α diversity) and increased structural diversity between stands (β diversity). Overall, disturbance‐mediated changes in forest structure and composition dampened future disturbance activity (a reduction of up to −67%), but were not able to fully compensate for the amplifying effect of climate change. Synthesis. Our findings indicate that the recent disturbance episode at the Bavarian Forest National Park was caused by a convergence of highly susceptible forest structures with climatic conditions favourable for bark beetle outbreaks. While future climate is increasingly conducive to massive outbreaks, the emerging landscape structure is less and less likely to support them. This study improves our understanding of the long‐term legacies of ongoing bark beetle disturbances in Central Europe. It indicates that increased diversity provides an important dampening feedback, and suggests that preventing disturbances or homogenizing post‐disturbance forests could elevate the future susceptibility to large‐scale bark beetle outbreaks.
... As a first analysis step, plots were grouped into two formerly managed (<100 years, n=20 and >100 years since last clearcut, n=33) and one old-growth (primary forest, n=30) categories. We chose 100 years as cut-off as we expected increasing disturbance activity and a stronger differentiation in forest structure for the second century of stand development, resulting in a diversification of forest attributes (Overbeck & Schmidt 2012;Donato et al. 2012;Meigs et al. 2017). Furthermore, 100 years represents the approximate rotation period in surrounding managed forests, with the cutoff distinguishing between forests that have been unmanaged for shorter/ longer periods than one rotation. ...
... development. An important factor promoting diverse stand development pathways are natural disturbances which can create gaps, promote variety in stand structures and lead to higher levels of deadwood stocks (Meigs et al. 2017;Senf et al. 2020). ...
Article
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Questions Primary forests fulfil important roles in preserving biodiversity, storing carbon and increasing ecological understanding. Yet, they have become very rare in Europe. An important policy goal is thus to increase the share of naturally developing forests by creating protected areas in formerly managed forests. Here, we investigated (1) if and how such forests return to conditions similar to old-growth, and (2) whether recently observed stand-replacing natural disturbances in combination with climate change set them onto an alternative development pathway. Location Dürrenstein Wilderness Area (IUCN Cat. Ib) in the Austrian Alps, containing the Rothwald, one of the last primary forest remnants of Central Europe. Methods We built a chronosequence of 87 plots, spanning 220 years of forest development after the cessation of management, and compared it to old-growth forests. We analyzed the recovery of nine attributes of forest composition, structure and functioning. To evaluate stand-level development of these attributes after recent natural disturbance and climate change, we additionally used a process-based simulation model. Results Old-growth forests showed a wide range of variability across investigated attributes. Forests converged to old-growth conditions after management ceased, with seven out of the nine attributes falling within the range of old-growth at the end of our chronosequence. The variation in tree diameters and the downed deadwood amount were, however, still significantly lower than in old-growth forests after 220 years of unmanaged stand development. Simulations did not indicate an alternative development pathway of recently disturbed stands. Conclusions While a full return to old-growth conditions can take centuries, a number of important forest attributes recover quickly, indicating that protecting formerly managed forests is a valuable strategy to enrich forest landscapes. Our results indicate that the mountain forests of Central Europe have high ecological resilience, developing towards old-growth conditions after both past management and current natural disturbance.
... The spatial patterns of trait distribution identified here may, in part, be a result of different disturbance regimes. In particular, low-intermediate severity disturbances foster forest development towards structural complexity (Franklin et al., 2002;Meigs et al., 2017). Fine-scale gap dynamics induced by wind and biotic disturbance agents dominate temperate and boreal-temperate forests of northeastern North America (Kosiba et al., 2018). ...
... In addition, climate change increases disturbance activity . Depending on disturbance size, frequency, and severity, future disturbances will have diverging impacts on forest development pathways and consequently on structural diversity (Donato et al., 2012;Meigs et al., 2017). For instance, an increase in small-scale disturbances may improve structural diversity, while large-scale disturbances reset forest succession starting with low structural complexity (Senf et al., 2020;Thom et al., 2017). ...
Article
Functional diversity (FD), represented by plant traits, is fundamentally linked to an ecosystem's capacity to respond to environmental change. Yet, little is known about the spatial distribution of FD and its drivers. These knowledge gaps prevent the development of FD-based forest management approaches to increase the trait diversity insurance (i.e., the response diversity) against future environmental fluctuations and disturbances. Our study helps fill these knowledge gaps by (i) mapping the current FD distribution, (ii) and analyzing FD drivers across northeastern North America. Following the stress-dominance hypothesis, we expected a strong environmental filtering effect on FD. Moreover, we expected abundant species to determine the bulk of FD distributions as suggested by the mass-ratio hypothesis. We combined a literature and database review of 44 traits for 43 tree species with terrestrial inventory data of 48,426 plots spanning an environmental gradient from northern boreal to temperate biomes. We evaluated the statistical influence of 25 covariates related to forest structure, climate, topography, soils, and stewardship on FD by employing an ensemble approach consisting of 90 non-parametric models. Temperate forests and the boreal-temperate ecotone east and northeast of the Great Lakes were identified as FD hotspots. Environmental filtering by climate was of secondary importance, with forest structure explaining most of the FD distribution of tree species in northeastern North America. Thus, our study provides only partial support for the stress-dominance hypothesis. Species abundance weightings altered trait diversity distributions and drivers only marginally, supporting the mass-ratio hypothesis. Our results suggest that forest management could increase FD without requiring knowledge of functional ecology by fostering stand structural complexity instead. Further, mixing species from different functional groups identified in this study can enhance the trait diversity insurance of forests to an uncertain future.
... Due to the considerable changes they generate in the overall structure of forest stands, and consequently, in micro-environmental conditions, windstorms represent stimulators of forest regeneration (Long et al., 1998;Panayotov et al., 2011;Bolte et al., 2014;Dobrowolska, 2015), enhance diversification of forest stands in terms of age, height and structure (Dobrowolska, 2015) and provide a chance for shade-intolerant and early-successional species to take advantage of the canopy opening created by tree falling (Bormann & Likens 1979;Peterson & Pickett, 1995). Most importantly, wind disturbance, as other types of natural disturbances, creates and maintains forest spatial heterogeneity (Seidl et al, 2014, Meigs et al., 2017Kulakowski et al., 2019). Because of the beneficial effects of wind disturbance on forest ecosystems, an increasing tendency to simulate wind disturbance in forest management practices and forest ecosystem modelling has been established during the last decades (Cooper-Ellis et al., 1999;Crow & Perera, 2004;Drever et al., 2005;Rammig et al., 2007;Seidl et al., 2014). ...
... So far, most studies about the impact of windstorms on forest ecosystems addressed the structural and compositional changes they produce in the tree layer and on forest regeneration (Peterson & Pickett, 1991, 1995Wolf et al., 2004;Bolte et al., 2014;Dobrowolska, 2015;Meigs et al., 2017;Rossi et al., 2017;Szwagrzyk et al., 2017;Meigs & Keeton, 2018) and at a lesser extent, their effects on soils (Schaetzl et al., 1989;Munthe et al., 2007;Š amonil et al., 2010) and insect communities (Bouget and Duelli, 2004). ...
Article
Catastrophic wind disturbance affects not only forest structure and regeneration, but also functional and compositional dynamics of the herbaceous layer. However, the issue of changes in functional diversity and functional trait values of the understory layer in response to wind disturbance has not been addressed so far. This study aims at investigating the patterns of variations in functional diversity, trait values and species richness of herbaceous species following wind disturbance. The study was carried out in the Piska Forest, a woodland complex in northern Poland, which was almost completely destroyed by a windstorm in 2002 and part of which was successively set aside to study the effects of natural disturbance on forest ecosystems. Vegetation surveys were conducted at 112 sample plots between 2014 and 2015. Four forest habitat types were identified and individually examined. The degree of disturbance severity was assessed as percentage of dead trees on all trees per surface unit. A set of twelve functional traits was assigned to the recorded species. Three functional diversity metrics (richness, evenness and divergence) were calculated based on the selected functional traits. We assessed the relationship between each of such metric and disturbance severity for each habitat type. The relationship between species richness and disturbance severity was also determined. We then estimated the relative importance of habitat type and disturbance severity on both functional diversity and species richness. Lastly, we examined the response of functional trait values to both disturbance severity and habitat type. Our results showed that wind disturbance effects on functional diversity are not univocal and that they strongly depend on habitat type. In fact, while in coniferous stands disturbance determined a decrease of functional divergence and left functional richness unaltered, in mixed-coniferous habitats it enhanced functional richness and did not affect functional divergence. In mixed-deciduous habitats, both functional richness and divergence decreased. In swamp habitats no major changes in functional diversity were observed. Changes in functional evenness were not significant. At the same time, disturbance significantly enhanced species richness in all forest habitats, but the coniferous one. It was not possible to clearly disentangle the relative contribution of disturbance and habitat type, since the two are strictly correlated. Out of the tested functional traits, only SLA, seed releasing height and share of stress-tolerant species exhibited significant response along the tested disturbance gradient. Most of the other traits reacted only to variations in the habitat type.
... and follows deterministic pathways connecting disturbance history and structural complexity (Donato et al., 2012;Meigs et al., 2017). ...
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Aim Natural disturbances influence forest structure, successional dynamics, and, consequently, the distribution of species through time and space. We quantified the long-term impacts of natural disturbances on lichen species richness and composition in primary mountain forests, with a particular focus on the occurrence of endangered species. Location Ten primary mountain spruce forest stands across five mountain chains of the Western Carpathians, a European hotspot of biodiversity. Methods Living trees, snags, and downed logs were surveyed for epiphytic and epixylic lichens in 57 plots. Using reconstructed disturbance history, we tested how lichen species richness and composition was affected by the current forest structure and disturbance regimes in the past 250 years. We also examined differences in community composition among discrete microhabitats. Results Dead standing trees as biological legacies of natural disturbances promoted lichen species richness and occurrence of threatened species at the plot scale, suggesting improved growing conditions for rare and common lichens during the early stages of recovery post-disturbance. However, high-severity disturbances compromised plot scale species richness. Both species richness and the number of old-growth specialists increased with time since disturbance (i.e. long-term uninterrupted succession). No lichen species was strictly dependent on live trees as a habitat, but numerous species showed specificity to logs, standing objects, or admixture of tree species. Main conclusions Lichen species richness was lower in regenerating, young, and uniform plots compared to overmature and recently disturbed areas. Natural forest dynamics and its legacies are critical to the diversity and species composition of lichens. Spatiotemporal consequences of natural dynamics require a sufficient area of protected forests for provisioning continual habitat variability at the landscape scale. Ongoing climatic changes may further accentuate this necessity. Hence, we highlighted the need to protect the last remaining primary forests to ensure the survival of regionally unique species pools of lichens.
... A third limitation is the focus on stand-replacing (at the grain of a 30 × 30 m pixel) disturbances, which is not able to fully account for the complexities of natural disturbance regimes in forest ecosystems, e.g. with regard to stands only partially affected by disturbance. Systems with low-to moderate-severity and/or mixed-severity disturbance are prevalent around the globe (Perry et al. 2011, Meigs et al. 2017. The resultant live tree legacies play an important role for the recovery from disturbances (Jõgiste et al. 2017), yet they cannot be satisfactorily described with the data used here. ...
Article
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Disturbance regimes are changing in forests across the world in response to global climate change. Despite the profound impacts of disturbances on ecosystem services and biodiversity, assessments of disturbances at the global scale remain scarce. Here, we analyzed natural disturbances in boreal and temperate forest ecosystems for the period 2001–2014, aiming to 1) quantify their within‐ and between‐biome variation and 2) compare the climate sensitivity of disturbances across biomes. We studied 103 unmanaged forest landscapes with a total land area of 28.2 × 106 ha, distributed across five continents. A consistent and comprehensive quantification of disturbances was derived by combining satellite‐based disturbance maps with local expert knowledge of disturbance agents. We used Gaussian finite mixture models to identify clusters of landscapes with similar disturbance activity as indicated by the percent forest area disturbed as well as the size, edge density and perimeter–area‐ratio of disturbed patches. The climate sensitivity of disturbances was analyzed using Bayesian generalized linear mixed effect models and a globally consistent climate dataset. Within‐biome variation in natural disturbances was high in both boreal and temperate biomes, and disturbance patterns did not vary systematically with latitude or biome. The emergent clusters of disturbance activity in the boreal zone were similar to those in the temperate zone, but boreal landscapes were more likely to experience high disturbance activity than their temperate counterparts. Across both biomes high disturbance activity was particularly associated with wildfire, and was consistently linked to years with warmer and drier than average conditions. Natural disturbances are a key driver of variability in boreal and temperate forest ecosystems, with high similarity in the disturbance patterns between both biomes. The universally high climate sensitivity of disturbances across boreal and temperate ecosystems indicates that future climate change could substantially increase disturbance activity.
... A large network of forest inventory plots was established along the Carpathian arc continuously sampled and resampled during the last decade (https://www.remoteforests.org/). The network includes 531 plots (0.1 ha) of monotypic primary forests of Picea abies (L.) Karst distributed on 40 forest stands located within four landscapes, in Slovakia, Ukraine and Northern and Southern Romania ( Fig. 1) (Janda et al., 2019;Meigs et al., 2017). P. abies mountain forests are widespread in the Slovak Low Tatras, Great Fatra and Small Fatra, where they can predominantly be found from 1200 to 1300 m a.s.l. up to the alpine zone (Holeksa et al., 2017). ...
Article
A tree's radial growth sequence can be thought of as an aggregate of different growth components such as age and size limitations, presence or absence of disturbance events, continuous impact of climate variability and variance induced by unknown origin. The potentially very complex growth patterns with prominent temporal and spatial variability imply that our understanding of climate-vegetation feedbacks essentially benefits from the expansion of large tree ring networks into data-poor regions, and our ability to disentangle growth constraints by comparing ring series at multiple scales. In this study, we analyze Central-Eastern Europe's most substantial assemblage of primary Norway spruce forests found in the Carpathian arc. The vast data set, >10,000 tree-ring series, is stratified along a prominent gradient in climate response space over four separate landscapes. We integrated curve intervention detection and dendroclimatic standardization to decompose tree growth variance into climatic, disturbance and residual components to explore the behavior of the components over increasingly larger spatial hierarchies. We show that the residual variance of unknown origin is the most prominent variance in individual Carpathian spruce trees, but at larger spatial hierarchies, climate variance dominates. The variance induced by climate was further explored with common correlation analyses, growth response to extreme climate years and forward modeling of tree growth to identify leading modes of climate response, and potentially non-linear and mixed climate response patterns. We find that the climatic response of the different forest landscapes overall can be described as an asymptotic response to June and July temperatures, most likely intermixed with influence from winter precipitation. In the collection of landscapes, Southern Romania stands out as being the least temperature sensitive and most likely exhibiting the most complicated mixed temperature and moisture limitation.
... In contrast, FoRTE's disturbance treatments targeted all tree species and multiple size classes and, as a result, diversified ratherthan reduced canopy height, leading to increases in complexity. That structural complexity may increase, decrease, or remain the same immediately after non-stand replacing disturbance is consistent with observations elsewhere Fahey et al. 2020;Meigs and Keeton 2018;Meigs et al. 2017;Peterson 2019;Reed et al. 2022), and counter to vegetation area, cover, and quantity measures, which consistently decline following disturbance (Parker 2020). ...
Article
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The temporal dynamics of forest canopy structure are influenced by disturbances that alter vegetation quantity and distribution. While canopy structural indicators such as leaf area index (LAI), canopy cover, and canopy height have been widely studied in the context of disturbance, the post-disturbance temporal dynamics of structural complexity, which summarizes the heterogeneity of vegetation arrangement, are poorly understood. With the goal of advancing conceptual and empirical understanding of the temporal dynamics of structural complexity following disturbance, we synthesized results from three large-scale disturbance manipulation experiments at the University of Michigan Biological Station (UMBS): the 4-year Forest Resilience Threshold Experiment (FoRTE) manipulating levels of disturbance severity; the decade-long Forest Accelerated Succession Experiment (FASET), in which all early successional tree species were stem-girdled within 39 ha in the same landscape; and forest chronosequences established following clear-cut harvesting. We found that the temporal dynamics of canopy structure following disturbance were dependent upon three factors: (1) the source and severity of disturbance; (2) the spatial and temporal scales of analysis; and (3) the measure of structure assessed. Unlike vegetation area index and canopy cover, which initially decreased in response to disturbance, structural complexity measures such as canopy and top rugosity did not consistently respond to moderate levels of disturbance severity. Over multi-decadal timescales, structural complexity increased to a maximum, regardless of whether fire occurred at the time of stand establishment, but intervening low-to-moderate severity disturbance in regrown century-old forests altered trajectories of canopy rugosity. We conclude that structural complexity indicators display a more nuanced temporal and directional response to disturbance than conventional leaf area and cover indexes. Predicting what disturbance conditions modify trajectories of structural complexity remains critical to disturbance characterization and the inference of ecosystem functioning.
... In europäischen Urwäldern existiert z. B. eine Vielzahl von Entwicklungspfaden nach einer Störung ( Meigs et al. 2017). Charakteristische Strukturen (z. ...
Chapter
Resilienz ist die Eigenschaft von Ökosystemen, sich wieder von Störungen zu erholen bzw. Störungen zu absorbieren, ohne dabei die systemimmanenten Strukturen und Prozesse zu verändern. Während sich die technische Resilienz allein auf eine Erholung nach Störungen fokussiert, berücksichtigt ökologische Resilienz die Möglichkeit eines Regimewechsels nach einer Störung. Ein Schlüsselelement der Resilienz ist der adaptive Kreislauf in Ökosystemen, also der Wechsel von Phasen des Wachstums, der Erhaltung, der Freisetzung und der Erneuerung. Wichtige Mechanismen der Resilienz gegenüber Störungen sind Interaktionen über räumliche und zeitliche Skalen, organische Reste nach Störungen, das ökologische Stressgedächtnis sowie die Reaktionsdiversität von Pflanzengemeinschaften.
... We analyzed spatiotemporal variation in climate-driven growth patterns since the year 1901 in a network of tree rings collected from fragments of primary monospecific Picea abies (L.) Karst forests spanning both latitudinal and altitudinal extents of the Carpathian arc ( Figure 1). Dendroecological disturbance history reconstruction has previously confirmed the advanced developmental status of these forest sites (Meigs et al., 2017;Schurman et al., 2018). By acknowledging the even distribution of forest structural and compositional variation among these broadly distributed forests, we are able to control for several important dimensions of biotic heterogeneity known to confound the determination of environmental change effects on ecosystem processes Parmesan & Yohe, 2003). ...
Article
Climatic constraints on tree growth mediate an important link between terrestrial and atmospheric carbon pools. Tree rings provide valuable information on climate‐driven growth patterns, but existing data tend to be biased towards older trees on climatically extreme sites. Understanding climate change responses of biogeographic regions requires data that integrate spatial variability in growing conditions and forest structure. We analyzed both temporal (c. 1901‐2010) and spatial variation in radial growth patterns in 9 876 trees from fragments of primary Picea abies forests spanning the latitudinal and altitudinal extent of the Carpathian arc. Growth was positively correlated with summer temperatures and spring moisture availability throughout the entire region. However, important seasonal variation in climate responses occurred along geospatial gradients. At northern sites, winter precipitation and October temperatures of the year preceding ring formation were positively correlated with ring width. In contrast, trees at the southern extent of the Carpathians responded negatively to warm and dry conditions in autumn of the year preceding ring formation. An assessment of regional synchronization in radial growth variability showed temporal fluctuations throughout the 20th century linked to the onset of moisture limitation in southern landscapes. Since the beginning of the study period, differences between high and low elevations in the temperature sensitivity of tree growth generally declined, while moisture sensitivity increased at lower elevations. Growth trend analyses demonstrated changes in absolute tree growth rates linked to climatic change, with basal area increments in northern landscapes and lower altitudes responding positively to recent warming. Tree growth has predominantly increased with rising temperatures in the Carpathians, accompanied by early indicators that portions of the mountain range are transitioning from temperature to moisture limitation. Continued warming will alleviate large‐scale temperature constraints on tree growth, giving increasing weight to local drivers that are more challenging to predict. This article is protected by copyright. All rights reserved.
... Extensive natural forest disturbances are very common in various forest ecosystems (Szwagrzyk, 2000). Natural disturbances that have always been present in forest his− tory may play a positive role in forest ecology (Thorn et al., 2017), especially in primeval forests (Trotsiuk et al., 2014;Čada et al., 2016;Meigs et al., 2017;Mikoláš et al., 2017), which are pro− tected in Europe. Abundant natural regeneration of forests is often observed after various dis− asters, such as e.g. ...
Article
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Damages caused by external (biotic and abiotic) factors generally cause losses in forest manage− ment, negatively affect the continuity of providing various ecosystem services, and therefore play an important role in the management of forest resources. The aim of the study was to present the type and extent of natural damages of commercial forests in the temperate climate of north− −eastern Poland (Central and Eastern Europe). In addition, a relationship between the occurrence of damage of a given type and the site type of forest, the age of the stand and species composition was investigated. The necessary information was obtained from the documentation of the State Forests National Forest Holding through an interactive form. Nearly 8% of the stands in north− −eastern Poland were damaged. Vast majority of the damage were attributed to wild herbivores-65%, followed by pathogenic fungi-24% and insects-8%. The degree of damage to stands depends on the source of damage, species and age of trees. 60% of damaged stands were damaged in 20%, and 1/3 in 10%. Animals most often damaged oaks; fungi-alders; insects-spruce. Fires most often damaged juniper, pine and birch. The most frequently damaged pine, oak and birch stands were characterized by the highest average age of trees (73.1; 56.0; 56.5 years, respectively). On the other hand, the least frequently damaged linden stands were characterized by the lowest average age of trees-45.1 years. Taking into account the influence of the forest site on the probability of damage to stands caused by natural factors, there are no significant differences between most sites. A slightly higher probability of damage to stands occurs in the moist forest site type, but the importance of this site in the study area is small. The paper indicates the exis− tence of a serious problem of damage to the young generation of the forest by wild herbivores. This poses a real threat to the preservation of forest sustainability-the renewal of some tree species, in the study area, animals caused significant damage to oak regeneration. We suggest discussing the necessity to limit the number of wild herbivores in commercial forests. The cur− rently used felling age, adopted for individual tree species, also requires discussion. As we have shown, the higher age of the stands contributes to more frequent damage.
... Thus, contrary to dominant even-aged management practices, natural dynamics silviculture aims to manage for a range of structures, including multi-aged or multi-cohort forest structures (O'Hara 1998). These are more analogous to the stand structures created by periodic partial mortality events and associated pulses of tree recruitment (Meigs et al. 2017). Large, infrequent disturbances are also a component of European natural disturbance regimes, but are more challenging to accommodate as a management objective (Turner et al. 1998). ...
Article
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In Europe, forest management has controlled forest dynamics to sustain commodity production over multiple centuries. Yet over‐regulation for growth and yield diminishes resilience to environmental stress as well as threatens biodiversity, leading to increasing forest susceptibility to an array of disturbances. These trends have stimulated interest in alternative management systems, including natural dynamics silviculture (NDS). NDS aims to emulate natural disturbance dynamics at stand and landscape scales through silvicultural manipulations of forest structure and landscape patterns. We adapted a “Comparability Index” (CI) to assess convergence/divergence between natural disturbances and forest management effects. We extended the original CI concept based on disturbance size and frequency by adding the residual structure of canopy trees after a disturbance as a third dimension. We populated the model by compiling data on natural disturbance dynamics and management from 13 countries in Europe, covering four major forest types (i.e., spruce, beech, oak, and pine‐dominated forests). We found that natural disturbances are highly variable in size, frequency, and residual structure, but European forest management fails to encompass this complexity. Silviculture in Europe is skewed towards even‐aged systems, used predominately (72.9% of management) across the countries assessed. The residual structure proved crucial in the comparison of natural disturbances and silvicultural systems. CI indicated the highest congruence between uneven‐aged silvicultural systems and key natural disturbance attributes. Even so, uneven‐aged practices emulated only a portion of the complexity associated with natural disturbance effects. The remaining silvicultural systems perform poorly in terms of retention as compared to tree survivorship after natural disturbances. We suggest that NDS can enrich Europe's portfolio of management systems, for example where wood production is not the primary objective. NDS is especially relevant to forests managed for habitat quality, risk reduction, and a variety of ecosystem services. We suggest a holistic approach integrating natural dynamics silviculture with more conventional practices.
... For this purpose, we explore extensive tree growth data from uneven-aged primary Norway spruce (Picea abies (L.) Karst) forests in the Carpathian Mountains (Central and Eastern Europe). In these forests, stand-replacing disturbances are uncommon, and forest dynamics is driven by disturbances highly varying in severity (Meigs et al., 2017). Since mostly not all trees are killed, structural development after disturbances continues in diverse paths with varying amounts of live and dead tree biomass (Trotsiuk et al., 2016). ...
Article
Accurate estimations of changes in the forest carbon (C) pools over time are essential for predicting the future forest C balance and its part in the global C cycle. While the overall understanding of global forest C dynamics has improved, some significant forest ecosystem processes have been largely overlooked, resulting in possible biases. As an example, the effects of low and moderate severity disturbances have received disproportionately little attention. In this study, we use an extensive database of 9610 tree increment cores from 400 plots in primary uneven-aged Norway spruce (Picea abies) forests in the Carpathian Mountains, to explore the dynamics of live and dead wood C after disturbance. The data represents a chronosequence of more than 250 years since disturbance, varying highly in severity. We found that disturbance severity had a substantial impact on the post-disturbance long-term accumulation of C. Initially, live tree C accumulated at a similar rate independent of disturbance severity. However, the increase in C leveled off earlier after low disturbance severity while the most heavily disturbed forests continued to accumulate C to the latest stages of stand development. These results stress the importance of taking disturbance severity into account when predicting the long-term dynamics of C storage in forests under climate change. The results also highlight the importance of these forests as significant C pools. If harvested and turned into managed forest they would not reach their maximum C storing capacity.
... Canopy trees influence the biotic and abiotic site variables, like light transmittance [18,29,35,[38][39][40][41], below-ground root competition for water and nutrients [42,43], soil organic layer, litter accumulation [44], and seed crop yield [19], which are important factors in determining establishment, growth, and survival of advance regeneration. The development of advance regeneration is significantly altered by disturbances (natural or human-made) which create openings in canopy layer [45][46][47]. Thinnings of the canopy of various intensities are an efficient way to improve the establishment and growth of advance regeneration [43,48] as well as to maintain regeneration for tree species with different shade tolerances [49]. ...
Article
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Continuous cover forestry (CCF) aims to emulate small natural disturbances and take advantage of natural regeneration. To implement these management practices successfully, knowledge of advance regeneration under the canopy in different conditions is crucial. Therefore, the aim of this study was to assess the influence of stand inventory parameters of canopy layer (age, basal area, height, and density) on the probability and density of advance regeneration of the Norway spruce (Picea Abies (L.) H. Karst.) and Scots pine (Pinus sylvestris L.) in hemiboreal forests in Latvia. The data were obtained from the National Forest Inventory, from a total of 879 plots. In the study, only Norway spruce or Scots pine dominated stands were used and the sampled stand age ranged from 21 to 218 years. The probability of advance regeneration differed between stands dominated by Scots pine versus Norway spruce. The probability and density of the advance regeneration of Norway spruce were positively linked to increased stand age, whereas the probability of the advance regeneration of Scots pine was negatively linked to the basal area of the stand. In stands dominated by Norway spruce and Scots pine on mesic soils, the advance regeneration of Norway spruce has a high density, whereas the advance regeneration of Scots pine is sporadic and scarce.
... In addition, such complex disturbance histories are evidence of both the strong resistance and resilience of boreal old-growth forests. Yet, recent studies have emphasized how moderate-severity disturbances can, in some cases, rejuvenate mature and old-growth stands Meigs et al. 2017). Similarly, our results illustrate that moderate severity disturbances, due to their abundance and regularity in the boreal forests of Eastern Canada, can probably lead to similar rejuvenation patterns. ...
Thesis
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La conservation des vieilles forêts, c’est-à-dire les peuplements dynamisés par les perturbations naturelles secondaires, dans les territoires aménagés du biome boréal est désormais un enjeu environnemental majeur. L’efficacité des mesures de gestion prises à leur encontre nécessite néanmoins une bonne connaissance des écosystèmes que l’on regroupe sous le terme « vieille forêt ». L’objectif de cette thèse est donc d’améliorer nos connaissances quant à la diversité, la dynamique et la conservation des vieilles forêts boréales résineuses dans les territoires aménagés de l’Est du Canada. Cette étude se concentre sur un territoire d’étude de 2200km2 situé dans le domaine bioclimatique de la pessière noire à mousse du Québec, Canada. Les caractéristiques structurelles de 74 peuplements, matures à surannés, y ont été échantillonnées. Des analyses dendrochronologiques ont aussi été réalisées pour 21 de ces sites. Enfin, nous avons utilisé les données des inventaires forestiers décennaux réalisés par le gouvernement du Québec depuis les années 60 pour observer l’évolution des vieilles forêts dans le territoire d’étude ainsi que l’acuité avec laquelle elles sont identifiées. Nos résultats montrent que les vieilles forêts boréales sont structurellement très diversifiées. Onze différentes structures ont ainsi pu être identifiées. Cette diversité résulte pour partie de la topographie mais augmente aussi avec le temps depuis la dernière perturbation majeure. La dynamique de perturbation secondaire de ces écosystèmes gagne aussi en complexité au fur et à mesure que la première cohorte, apparue suite à la dernière perturbation majeure, est remplacée par de nouvelles cohortes, renforçant cette diversité structurelle. Au début du processus de transition vers l’état de vieille forêt, les perturbations de sévérité faible dominent mais les perturbations de sévérité modérée gagnent progressivement en importance, jusqu’à atteindre un niveau similaire à celui des perturbations de sévérité faible. Les épidémies de tordeuse des bourgeons de l’épinette (Choristoneura fumiferana, Clemens) apparaissent alors comme un élément clé de cette dynamique de perturbations secondaires, indépendamment de leur sévérité. En comparaison des feux de forêt, l’aménagement forestier a récolté une plus grande proportion de vieilles forêts (se définissant ici par un âge supérieur à 100 ans) sur ce territoire, notamment caractérisées par un volume de bois marchand plus important. L’influence de l’exploitation forestière sur la diversité structurelle du territoire diffère donc de celle du feu. Par ailleurs, le plus récent inventaire photographique aérien réalisé par le gouvernement du Québec sous-estimait fortement l’abondance des vieilles forêts sur le territoire d’étude. La majorité de ces peuplements, se définissant sur le terrain par une structure complexe, étaient identifiés comme des peuplements équiens (c’est- à-dire structurellement simples) par l’inventaire aérien. Des seuils inadaptés à la forêt boréale ainsi que l’absence d’éléments de vieilles forêts particulièrement visibles par télédétection ou suivant une observation superficielle du peuplement peuvent expliquer ces résultats. Une fois le stade de vieille forêt atteint, les peuplements forestiers boréaux continuent donc de suivre une dynamique complexe, ce qui peut mener à de nombreux changements structuraux dans le temps. La diversité des vieilles forêts boréales doit donc être reconnue dans l’aménagement forestier, car impliquant la présence de nombreux types d’habitats nécessaires à la biodiversité. Nos résultats montrent cependant que les peuplements récoltés en priorité sont les vieilles forêts avec la plus forte valeur marchande. Ignorer cette diversité – par exemple en se retreignant à un simple pourcentage de vieilles forêts à conserver, qu’importe leur type – pourrait donc mener à une réduction de la diversité structurelle des vieilles forêts en territoire aménagé, causant à terme une perte d’habitat. Dans l’état actuel des choses, les inventaires photographiques aériens ne permettent pas de reconnaître la diversité des vieilles forêts, ce qui empêche la mise en place de stratégies efficaces. Intégrer de manière durable les vieilles forêts boréales dans l’aménagement forestier demande par conséquent non-seulement la reconnaissance de la richesse et de la complexité de ces écosystèmes, mais aussi le développement d’outils permettant d’assurer l’identification des nombreuses formes sous lesquelles elles peuvent se présenter. Maintaining old-growth forests, i.e. stands driven by gap-dynamics, in managed boreal landscapes is a major environmental issue. The efficacy of old-growth forests conservation strategies depends however on an adequate knowledge about these ecosystems. The objective of this thesis is therefore to improve our knowledge about the diversity, the dynamics and the conservation values of boreal old-growth forests in manged landscapes. This study focuses on a 2200km2 territory situated in Québec’s black spruce – feathermoss bioclimatic domain, Canada. We sampled the structural characteristics of 74 stands that were mature to very old. We also performed dendrochronological analysis on 21 of these sites. Finally, we also used Québec’s decadal forest surveys data sampled since the 1960’s to observe the evolution of old-growth forest characteristics on the study territory, as well as the accuracy of these surveys in identifying old-growth stands. According to our results, boreal old-growth forests are structurally diversified. 11 different old-growth forests structures have been identified. This diversity is in part a result of topography but also of time since the last stand-replacing disturbance. Secondary disturbances dynamics increase in complexity while the first cohort, which appeared following the last stand-replacing disturbance, is replaced by new cohorts. At the beginning of the transition process toward the old-growth stage, a low severity defines most of the secondary disturbances but moderate severity disturbances progressively gain in importance. When the true old-growth stage is reached, low and moderate severity disturbances are equal in importance in stand dynamics. Most of these disturbances seems to result from spruce budworm (Choristoneura fumiferana, Clemens) outbreaks, independently of disturbance severity. In comparison to forest fires, most of the stands logged on the study territory were old-growth stands (here defined by an age superior to 100 years) characterized by higher merchantable wood volume. Logging activities have therefore an influence on landscape structural diversity which differs from that of fire. Moreover, the most recent photographic aerial survey performed by Québec’s government significantly underestimated old-growth forests abundance on this territory. Most of these stands, defined by a complex structure based on field surveys, were identified as even-aged (i.e. structurally simple) by the aerial survey. Unsuitable thresholds for boreal forests as well as the absence of particularly visible old-growth attributes were the main factors that may explain the low accuracy of aerial surveys. The dynamics of boreal old-growth forests is complex, especially once the true old-growth stage reached. For this reason, the structure of old-growth stands may significantly change over time. Boreal old-growth forest structural diversity must be explicitly acknowledged by forest managers, because it implies the presence of different habitats among old-growth stands and therefore different species. However, logging activities cut in priority old-growth forests with the highest economic value, as indicated by our results. Ignoring this diversity (e.g. by only defining a given percentage of old-growth forests that must be maintained in managed landscapes, regardless of their structure) could therefore lead to the erosion of boreal old-growth forest diversity, causing biodiversity issues because of the disappearance of specific habitats. In addition, orthographic forest surveys are currently not accurate enough to identify boreal old-growth forests and discriminate their structures, hence limiting the development of efficient management strategies. The integration of boreal old-growth forests in sustainable forest management therefore requires first the acknowledgement of the diversity and the complexity of these ecosystems and second, the development of accurate tools capable of identifying all the forms of boreal old-growth forests.
... Moreover, the "complexity challenge" related to old-growth forests is not restricted to the boreal forests of eastern Canada. The complexity of oldgrowth forests has been highlighted in temperate forests in North America [18,56,57], as well as in Europe, in boreal [16,58,59] and temperate forests [60][61][62]. Since old-growth temperate forests in Asia, Oceania, and South America share similar attributes with those in Europe and North America [63], it is also likely that we observe similar dynamic patterns in these regions. ...
Article
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Research Highlights: Radial growth patterns of trees growing in old-growth boreal forests in eastern Canada can be grouped into a small number of simple patterns that are specific to different old-growth forest types or successional stages. Background and Objectives: Identifying the main radial growth trends in old-growth forests could help to develop silvicultural treatments that mimic the complex dynamics of old-growth forests. Therefore, this study aimed to identify the main radial growth patterns and determine how their frequencies change during forest succession in old-growth forests, focusing on boreal landscapes in eastern Canada. Materials and Methods: We used dendrochronological data sampled from 21 old-growth stands in the province of Quebec, Canada. Tree-ring chronologies were simplified into chronologies of equal length to retain only primary growth trends. We used k-means clustering to identify individual growth patterns and the difference in growth-pattern frequency within the studied stands. We then used non-parametric analyses of variance to compare tree or stand characteristics among the clusters. Results: We identified six different growth patterns corresponding to four old-growth forest types, from stands at the canopy breakup stage to true old-growth stands (i.e., when all the pioneer cohort had disappeared). Secondary disturbances of low or moderate severity drove these growth patterns. Overall, the growth patterns were relatively simple and could be generally separated into two main phases (e.g., a phase of limited radial increment size due to juvenile suppression and a phase of increased radial increment size following a growth release). Conclusions: The complexity of old-growth forest dynamics was observed mainly at the stand level, not at the tree level. The growth patterns observed in true old-growth forests were similar to those observed following partial or stem-selection cuts in boreal stands; thus, these silvicultural treatments may be effective in mimicking old-growth dynamics.
... Forest Ecology and Management 464 (2020) 118055 Douglas-fir seedlings to create uniform, dense stands that transition into closed canopy stands in less than 20 years and harvest rotations of approximately 40 years. Stand age is often used as a covariate in ecological investigations, but the influence of management intensity on populations and communities at stand and watershed scales has received little research attention (Homyack and Kroll, 2014;Meigs et al., 2017). In summary, following stand-replacing disturbance on federal lands, far more energy is likely to be available to non-conifers (lower half of yaxis in Fig. 1), and a greater diversity and abundance of standing and coarse wood (right half of x-axis in Fig. 1) will be present relative to private lands. ...
Article
The ecological value of unmanaged early successional habitat created by disturbances has received considerable research attention. Less well studied is the capacity of tree plantations to contribute to local and regional biological diversity while subsidizing conservation strategies. We present a conceptual framework for describing variability in early successional forests and illustrate how the spatial pattern of this habitat may vary as a function of productivity, land ownership, and disturbance in the Pacific Northwest, USA. We posit that plantations will only increase in ecological and economic importance as the world addresses conservation and resource production challenges associated with climate change, altered disturbance regimes, increasing rates of global wood consumption, and evolving social, legal, and economic expectations. Researchers and managers can foster collaborative frameworks to encourage provisioning of non-timber services on private land, while prioritizing non-timber benefits of early successional habitat on public land to optimize biodiversity conservation and ecosystem services provided in managed forest landscapes.
... A third limitation is the focus on stand-replacing (at the grain of a 30 × 30 m pixel) disturbances, which is not able to fully account for the complexities of natural disturbance regimes in forest ecosystems, e.g. with regard to stands only partially affected by disturbance. Systems with low-to moderate-severity and/or mixed-severity disturbance are prevalent around the globe (Perry et al. 2011, Meigs et al. 2017. The resultant live tree legacies play an important role for the recovery from disturbances (Jõgiste et al. 2017), yet they cannot be satisfactorily described with the data used here. ...
Article
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Disturbance regimes are changing in forests across the world in response to global climate change. Despite the profound impacts of disturbances on ecosystem services and biodiversity, assessments of disturbances at the global scale remain scarce. Here, we analyzed natural disturbances in boreal and temperate forest ecosystems for the period 2001–2014, aiming to 1) quantify their within‐ and between‐biome variation and 2) compare the climate sensitivity of disturbances across biomes. We studied 103 unmanaged forest landscapes with a total land area of 28.2 × 10⁶ ha, distributed across five continents. A consistent and comprehensive quantification of disturbances was derived by combining satellite‐based disturbance maps with local expert knowledge of disturbance agents. We used Gaussian finite mixture models to identify clusters of landscapes with similar disturbance activity as indicated by the percent forest area disturbed as well as the size, edge density and perimeter–area‐ratio of disturbed patches. The climate sensitivity of disturbances was analyzed using Bayesian generalized linear mixed effect models and a globally consistent climate dataset. Within‐biome variation in natural disturbances was high in both boreal and temperate biomes, and disturbance patterns did not vary systematically with latitude or biome. The emergent clusters of disturbance activity in the boreal zone were similar to those in the temperate zone, but boreal landscapes were more likely to experience high disturbance activity than their temperate counterparts. Across both biomes high disturbance activity was particularly associated with wildfire, and was consistently linked to years with warmer and drier than average conditions. Natural disturbances are a key driver of variability in boreal and temperate forest ecosystems, with high similarity in the disturbance patterns between both biomes. The universally high climate sensitivity of disturbances across boreal and temperate ecosystems indicates that future climate change could substantially increase disturbance activity.
... Disturbances play a fundamental role in forest dynamics and in combination with environmental factors, they shape forest ecosystems, particularly spatial and age structures, quantity of biomass, species composition, and overall biodiversity (White and Pickett, 1985). Historically, complex mixed-severity disturbance regimes have prevailed in European mountain forest ecosystems (Seidl et al. 2011a, Meigs et al. 2017, Kulakowski et al. 2017. However, climate change has increased disturbance frequency and severity during recent decades (Seidl et al. 2011b, Turner 2010, Raffa et al. 2008, Schurman et al. 2018, which has in turn increased their effects on forest understories and biodiversity (Stevens et al. 2015, Dietz et al. 2020, Zellweger et al. 2020. ...
Article
Development of primary spruce forests is driven by a series of disturbances, which also have an important influence on the understorey vegetation and its diversity. Early post-disturbance processes have been intensively studied, however, very little is known about the long-term effects of disturbances on the understorey. We quantified disturbance history using dendrochronological methods to investigate its impact on vascular plant diversity and understorey species composition. We sampled 141 plots randomly assigned throughout primary stands located in the zone of natural montane acidophilous forests dominated by Picea abies (L.) Karst. in the Western Carpathians. Dendrochronological, dendrometric, and environmental parameters were related to understorey properties using ordination methods and a Bayesian approach using multilevel linear models (GLMM). Time since the last disturbance (23–260 years ago; mostly windstorms and bark beetle outbreaks) had a significant effect on understorey species composition of the current communities, and it also interacted with disturbance severity to influence species diversity. The effect of disturbances on the understorey was largely mediated by the alteration of stand structure (age, DBH, canopy openness), Vaccinium myrtillus L. cover, and topsoil chemical properties. A period of severe disturbances between 1860 and 1890 resulted in a legacy of our current, relatively homogeneous spruce stands with less diverse sciophilous understorey dominated by V. myrtillus, which is in contrast to heterogeneous stands (in terms of age and spatial structure) driven by small-scale, lower-severity disturbances, which led to an understorey enriched by species with higher demands on light and topsoil quality (higher K concentration and lower C/N ratio). All developmental pathways following disturbances create a unique complex of spatiotemporal understorey variability in the montane spruce forests. Therefore, to preserve their full diversity, disturbances of all severities and sizes should be accepted as natural drivers, both in the field of nature conservation and close-to-nature forestry efforts.
... For example, the SWR treatment was correlated with significantly higher sapling diversity. We expect the release effect of this and other treatments will become even more evident in the future, leading to a more diverse forest composition and likely also enhanced structural complexity in the long term (D'Amato et al., 2011;Meigs et al., 2017;Keeton et al., 2018). As control plots showed only moderate variation in canopy openness (4.5%−12.3%, ...
Article
Disturbance-based silviculture is of increasing interest as an approach to provide multiple ecosystem services and beta diversity in habitat conditions. One such approach increasingly employed in the eastern U.S. is a set of forestry practices developed to diversify forested bird habitats, called Silviculture with Birds in Mind (SBM). While strongly appealing to many private landowners, empirical data have not yet been reported regarding the effects of SBM treatments on forest structure and dynamics and how they compare to natural disturbances. Moreover, the potential of bird-oriented silviculture like SBM to enhance co-benefits, for instance, by retaining high carbon stocks in managed forests, has not been investigated. The objectives of our study were thus (i) to analyze the effects of SBM treatments on forests and compare them with natural disturbances, and (ii) to assess the co-benefits of multiple habitat indicators and carbon storage within three years of silvicultural treatment in mature northern hardwood-conifer forests. We derived 14 stand structural variables as well as carbon storage from 217 SBM inventory plots, and compared them with the effects of intermediate-severity wind disturbance using non-metric multidimensional scaling (NMDS). Subsequently, we applied multi-hierarchical Bayesian models to investigate SBM treatment effects on aboveground carbon storage, as well as on four key habitat indicators. We also used Bayesian models to derive the relationships between habitat indicators and carbon storage. SBM treatments created a diversity of post-harvest stand conditions and, while having lower values for some structural characteristics in comparison to controls, significantly enhanced the variation in individual structural elements. Moreover, the treatments were closer in ordinal space to the irregular structure associated with intermediate-severity wind disturbance than untreated control plots. However, the NMDS indicated that SBM treatments did not fully approximate partial wind disturbances. Carbon storage was positively associated with stand structural complexity. Disturbance-based approaches like SBM help diversify habitat conditions and we expect these effects to become more pronounced as stands respond to the treatments over time. If applied more broadly, treatments targeted at diversifying habitats would also help maintain high carbon stocking at landscape scales. However, as the treatments do not fully emulate the region’s natural disturbance regime, we propose widening the portfolio of multi-cohort, retention, and gap-based silvicultural approaches in landscape-scale management.
... Contemporary ecology recognizes the fundamental role of natural disturbances and tree mortality processes in the dynamics of forest structural development and thus habitat availability for the full range of biodiversity, associated with different successional stages (Franklin et al. 2002, Holeksa et al. 2007, Nagel et al. 2013, Battisti et al. 2016. Recently, a mixed-severity disturbance regime was identified as a dominant process shaping the dynamics of Carpathian Norway spruce (Picea abies) ecosystems , Meigs et al. 2017, Schurman et al. 2018), a finding confirmed specifically for the western Carpathians as well ). This regime is characterized by disturbances of varying spatial scale and severity (percentage of killed trees in a given area), including large-scale events caused by windstorms and bark beetles as well as gap-forming and intermediate intensity events . ...
Article
Understanding the processes shaping the composition of assemblages in response to disturbance events is crucial for preventing ongoing biodiversity loss in forest ecosystems. However, studies of forest biodiversity responses to disturbance typically analyze immediate or short-term impacts only, while studies relating long-term disturbance history to biodiversity assemblage dynamics are rare. To address this important knowledge gap, we used a dendroecological approach to link natural disturbance history of 250 years (1750-2000) to structural habitat elements and, in turn, to breeding bird assemblages. We used data collected in 2017 and 2018 from 58 permanent study plots within 10 primary spruce forest stands distributed across the Western Carpathian Mountains of Europe. This dataset contained breeding bird counts and environmental variables describing forest density, tree diameter distribution, tree height, tree microhabitats, deadwood quantity and quality, and regeneration. Bird assemblages were significantly influenced by forest structure which was in turn shaped by disturbance dynamics (disturbance frequency, time since the last disturbance and its severity). Early successional species associated with more open habitats were positively influenced by disturbance-related structure (i.e. deadwood-related variables, canopy cover), while some species responded negatively. At the same time, overall abundance, species richness and Shannon diversity of the bird assemblage remained unchanged under variable disturbance histories. Our results support a view of primary spruce forests as a highly dynamic ecosystem, harbouring populations of bird species at all stages of succession despite significant structural changes and shifting patch mosaics over time due to natural disturbances.
... This suggests alternations between aggregated disturbances increasing inter-patch variation and hence causing differentiation of the forest structure and more evenly distributed events involving extensive areas and having a homogenizing effect. These results thus do not support the hypothesis of a uniform spatial pattern of disturbances in the studied ecosystems but rather show that this pattern varies and hence introduces spatio-temporal heterogeneity into the forest landscape and creates multiple developmental pathways (Meigs et al., 2017). ...
Article
Disturbances have been recognized as a key factor shaping the species composition, structure and dynamics of natural forest ecosystems. In Europe, where forests driven by spontaneous processes have survived in relic form, knowledge about natural disturbance regimes is still fragmentary. To expand this knowledge, we reconstructed stand-level growth and analyzed the spatio-temporal pattern of release signals in the increment chronologies of individual trees as indicators of disturbance events in the Western Carpathians (Central Europe). The study was carried out in five old-growth forests formed by Fagus sylvatica L., Abies alba Mill. and Picea abies (L.) H. Karst. Depending on the stand, the analyses included tree-ring series of 84–193 trees sampled over areas of 5.9–13.6 ha and aimed at determining (1) the spatio-temporal pattern of disturbance severity over the last two centuries, (2) whether disturbances have been synchronized in time across the study sites and (3) whether disturbances have induced pulsed dynamics of stand development manifested as fluctuations in radial tree increment at the level of entire stands. In the period 1850–2010, the percentage of decades with the proportion of released trees < 10, 10–20, 20–30 or more than 30% was 38, 41, 14 and 7%, respectively, and no instances of severe disturbances simultaneously impacting an extensive area and releasing the vast majority of trees were found. The release events were only weakly synchronized at the between-stand level. The spatial distribution of released trees varied over the decades, with a shift toward spatial independence for the most severe disturbances. At the stand level, the interchanging periods of increasing/decreasing tree growth lasted between 24 and 36 years, with the exception of one stand in which this period lasted 54 years. The revealed fluctuations in tree growth attributable to changes in stand density were relatively small and accounted on average for 7% of the total variation in annual tree increments. This suggests that local level disturbances introduce structural heterogeneity and strongly modify tree growth, but at the stand level, their effect is dispersed and causes only minor fluctuations. An over-dispersion of decadal release frequencies compared to the random model and spatial correlation of disturbing events on the one hand, and the lack of extensive disturbances, frequent occurrence of multiple releases in tree life histories, and small fluctuations in the reconstructed growth at the stand level on the other hand, suggest a disturbance regime which goes beyond random processes in a strict sense and is thus not entirely compatible with the classical model of gap-phase stand dynamics.
... For this reason, old-growth forests are often viewed as models to be emulated for promoting naturalness and biodiversity conservation in managed stands (Bauhus et al., 2009;Puettmann et al., 2009;Keeton et al., 2019). However, recent research emphasized that the term "old-growth forest" encompasses a wide variety of changing forest structures at the stand scale (Halpin and Lorimer, 2016;Meigs et al., 2017;Kozák et al., 2020). Consequently, it is likely that the composition of TreM and deadwood will significantly vary from one oldgrowth structure to another. ...
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Tree-related microhabitats (TreM) and deadwood are two forest attributes providing essential resources for biodiversity conservation and ecosystem services. Old-growth forests are generally defined by a high abundance and diversity of TreM and deadwood, but little is known about TreM and deadwood dynamics once the old-growth stage is reached, in particular in the boreal biome. In this context, knowledge on TreM and deadwood dynamics in old-growth forest stands is necessary to better understand how these forests contribute to biodiversity and ecosystem services. The aim of this study is thus to determine how TreM, and deadwood abundance and diversity vary within boreal old-growth forests. To reach this objective, we surveyed TreM and deadwood attributes, as well as structural and abiotic attributes, in 71 boreal old-growth forests situated in Quebec, Canada. We used hierarchical clustering analysis to identify TreM and deadwood abundance and diversity patterns in the studied stands. We identified five clusters of TreM and deadwood characteristics, which corresponded to three stages of old-growth forest succession: canopy break-up (beginning of the old-growth stage), transition old-growth stage (replacement of the first cohort by old-growth cohorts) and true old-growth stage (first cohort all or almost all gone). The peak in TreM richness and diversity was reached at the transition old-growth stage, whereas the peak for deadwood richness and diversity was reached at the true old-growth stage. Overall, true old-growth forests were defined by a combination of moderate to high TreM density and high deadwood volume, but these values significantly varied among stands depending on past secondary disturbances, stand structure and its composition (black spruce [Picea mariana Mill.] dominated vs mixed black spruce – balsam fir [Abies balsamea (L.) Mill.]). These results therefore underscore the importance of considering old-growth forests as dynamic rather than static ecosystems, as the composition of tree- and deadwood-related microhabitats in the same old-growth stand may markedly change over time. At landscape scale, these results also imply that the mosaic of habitats present in old-growth forests can vary greatly from one location to another, highlighting the importance of maintaining a diversity of old-growth forest structure and composition.
... Maintaining large and continuous areas of oldgrowth forest, or at least emulating their characteristics in managed stands, has therefore become a major forest management issue (Bauhus et al. 2009, Freibauer 2009, Gauthier et al. 2009). Recent studies have, however, emphasized that rather than being homogeneous entities, oldgrowth forests consist of a mosaic of stands that vary in their composition and structure, a pattern dependent on both stand conditions and disturbance history (Halpin and Lorimer 2016, Meigs et al. 2017, Martin et al. 2018. Knowing many species are related to old-growth forest attributes (Rheault et al. 2009, Fenton and Bergeron 2011, Koz ak et al. 2021, it is essential to distinguish the relative importance of heterogeneity within old-growth forests. ...
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Old‐growth forests are optimal habitats for many woodpeckers, which are often themselves excellent indicators of deadwood‐associated biodiversity. Old‐growth forests are, however, heterogeneous ecosystems in terms of structure, composition, and deadwood characteristics, thus implying a varied use of these forests by woodpeckers. In boreal landscapes, old‐growth stands are threatened by forest harvesting; however, there is little information in regard to the consequences for biodiversity with the loss of specific types of old‐growth forests. This study aimed to assess how the black‐backed woodpecker (Picoides arcticus), a biodiversity indicator species associated with old‐growth forest attributes, uses different types of old‐growth forests for its foraging needs. We identified woodpecker foraging marks in 24 boreal old‐growth forest stands in eastern Canada that were dominated by black spruce (Picea mariana), located within the home range of eight black‐backed woodpeckers. We identified the various old‐growth forest types using a typology based on the structural attributes of old‐growth stands. We classified the sampled stands into four old‐growth forest types, corresponding to different successional stages (recent or old, relative to the onset of the old‐growth stage), composition (pure black spruce or mixed black spruce–balsam fir [Abies balsamea]), and productivity (ongoing paludification or not). The black‐backed woodpecker foraged in all types of old‐growth forests, but favored dense old‐growth forests that were not paludified and that showed a high temporal continuity (i.e., old‐growth dynamics probably started more than a century ago). The temporal continuity of the old‐growth state allows for the continuous supply of large, slightly decayed snags, the preferred foraging substrates of the black‐backed woodpecker. The old‐growth forest type most favored by this woodpecker is, however, also the forest type most often targeted first by logging operations. Protecting the biodiversity associated with recent deadwood in managed areas thus requires maintaining a sufficient area and density of dense, old‐growth black spruce‐dominated forests in managed areas.
... Forests that exhibit reverse J-shaped distributions are more structurally complex by having a diversity of tree size and age classes yet such a distribution might not be within the range of natural dynamics of primary spruce forests because they have been historically shaped by mixed-severity disturbances (e.g. Č ada et al., 2016;Meigs et al., 2017). ...
Article
Natural disturbances strongly influence forest structural dynamics, and subsequently stand structural heterogeneity, biomass, and forest functioning. The impact of disturbance legacies on current forest structure can greatly influence how we interpret drivers of forest dynamics. However, without clear insight into forest history, many studies default to coarse assumptions about forest structure, for example, whether forests are even or unevenly aged. The aim of this study was to analyze the effects of past disturbances on the current diameter distributions of Norway spruce (Picea abies (L.) Karst.)-dominated landscapes throughout the Carpathian Mountains. Our dendroecological dataset comprises tree cores from 339 plots (7,845 total tree cores), nested within 28 primary forest stands, known to vary greatly in the severity of historical disturbances. Our analyses revealed that historical disturbances had a strong and significant effect on the current diameter distribution shapes at the plot level. We demonstrated that mixed-severity disturbance regimes were more frequent and create a complex pattern of diameter distributions at the plot and stand scale. Here, we show that high severity disturbance was associated with unimodal diameter distributions, while low and moderate severity was associated with the reverse J-shaped distribution. This is a result of complex disturbance patterns, with structural biological legacies. Our results will have important management implication in the context of tree size heterogeneity, biomass storage, and productivity as influenced by natural disturbances. Lastly, these results demonstrate that structural changes may arise as consequences of changing disturbance regime associated with global change.
... Old-growth forests are complex ecosystems whose structure is shaped by primary and secondary disturbances, tree species composition, as well as environmental conditions (Martin et al., 2021a(Martin et al., , 2018Meigs et al., 2017). In addition to assessing the accuracy of the previously defined models, we therefore considered it important to evaluate whether the model predictions were ecologically consistent, or if unidentified biases in the study area (e.g. ...
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Old-growth forests of different ages provide specific structures, habitats and ecosystem services. Methods to distinguish this internal diversity are still rare, especially in boreal forests. This research therefore aims to determine the ability of Airborne Laser Scanning (ALS) technology to identify age-related structural diversity in old-growth boreal forests. The study area was located in primary boreal forests in Quebec (Canada) dominated by black spruce (Picea mariana). This area contained 71.8 km² of early old-growth forests (burned 110 years ago), 17.1 km² of late old-growth forests (protected areas; unburned for at least 250 years) and 370 km² of old-growth forests of unknown age (> 125-years-old). We divided the study area into 1 ha tiles, where we extracted seven ALS indices representing vertical and horizontal forest structure. We trained random forest models using an iterative approach to discriminate between early and late old-growth forests based on ALS indices. Model predictions were applied to the old-growth tiles of unknown age, and to 86 field plots (28 from provincial forest surveys and 58 from a dedicated survey of old-growth forests) to evaluate the predictive capacity of the models. The models very accurately distinguished early and late old-growth forests (error-rate = 4.9%). Old-growth survey plots confirmed model ability to discriminate early and late old-growth forests, but not provincial survey plots, possibly because of a lower reliability of these data when forest age exceeds 150 years. Model predictions for tiles of unknown age highlighted the presence of very large tracts of late old-growth forests within a matrix of old-growth forests of intermediate age (≈150–200 years). Overall, ALS-data can contribute to a finer structural age distinction and mapping of boreal old-growth forests. This enhanced knowledge of old-growth landscapes will greatly help to improve their protection, restoration and management. The scarcity of reliable field data for model evaluation is, however, a limitation to be addressed.
... (3) management systems are increasingly optimized to reduce impact 39 and many natural disturbances that occur frequently (that is, bark beetle infestations and small-scale wind-throw) are characterized by mixed severity 40 . ...
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Changes in forest disturbances can have strong impacts on forests, yet we lack consistent data on Europe’s forest disturbance regimes and their changes over time. Here we used satellite data to map three decades of forest disturbances across continental Europe, and analysed the patterns and trends in disturbance size, frequency and severity. Between 1986 and 2016, 17% of Europe’s forest area was disturbed by anthropogenic and/or natural causes. We identified 36 million individual disturbance patches with a mean patch size of 1.09 ha, which equals an annual average of 0.52 disturbance patches per km2 of forest area. The majority of disturbances were stand replacing. While trends in disturbance size were highly variable, disturbance frequency consistently increased and disturbance severity decreased. Here we present a continental-scale characterization of Europe’s forest disturbance regimes and their changes over time, providing spatial information that is critical for understanding the ongoing changes in Europe’s forests. Changes in forest disturbance affect their sustainability. This study finds that between 1986 and 2016, 36 million disturbances by humans or other causes affected 17% of Europe’s forest area.
... The new structures that result from natural disturbances, like an increased amount of dead wood, open canopy, a diverse understory, vertical diversification. and spatial heterogeneity (Meigs et al., 2017;Senf et al., 2020;Swanson et al., 2011), can provide habitat for rare or endangered species (Bässler & Müller, 2010;Mikol as et al., 2017). For example, Aculeata, Syrphidae and Formicidae can benefit from open forests with warmer microhabitats (Beudert et al., 2015;Lehnert et al., 2013). ...
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Natural disturbances are increasing around the globe, also impacting protected areas. Although previous studies have indicated that natural disturbances result in mainly positive effects on biodiversity, these analyses mostly focused on a few well established taxonomic groups, and thus uncertainty remains regarding the comprehensive impact of natural disturbances on biodiversity. Using Malaise traps and meta-barcoding, we studied a broad range of arthropod taxa, including dark and cryptic taxa, along a gradient of bark beetle disturbance severities in five European national parks. We identified order-level community thresholds of disturbance severity and classified barcode index numbers (BINs; a cluster system for DNA sequences, where each cluster corresponds to a species) as negative or positive disturbance indicators. Negative indicator BINs decreased above thresholds of low to medium disturbance severity (20%-30% of trees killed), whereas positive indicator BINs benefited from high disturbance severity (76%-98%). BINs allocated to a species name contained nearly as many positive as negative disturbance indicators, but dark and cryptic taxa, particularly Diptera and Hymenoptera in our data, contained higher numbers of negative disturbance indicator BINs. Analyses of changes in the richness of BINs showed variable responses of arthropods to disturbance severity at lower taxonomic levels, whereas no significant signal was detected at the order level due to the compensatory responses of the underlying taxa. We conclude that the analyses of dark taxa can offer new insights into biodiversity responses to disturbances. Our results suggest considerable potential for forest management to foster arthropod diversity, for example by maintaining both closed-canopy forests (>70% cover) and open forests (<30% cover) on the landscape.
... Studies of contemporary moderate disturbances support these results and suggest that these events introduce heterogeneity at small, but also moderate stand scales, and they generate important live and dead biological legacies, while usually maintaining stand resistance, resilience, biodiversity, and late-successional species composition by favoring advanced regeneration (Stueve et al. 2011, Meigs andKeeton 2018). The stand heterogeneity that developed as a result of these events and their frequent occurrence suggests that moderate disturbances are the key to the creation and maintenance of forest structural complexity over time rather than a linear development path without any disturbance events ( Cada et al. 2016, Meigs et al. 2017. A nonrandom spatial distribution of disturbance events seems to be a characteristic of moderate-scale wind and bark-beetle disturbances. ...
Article
Estimates of historical disturbance patterns are essential to guide forest management aimed at ensuring the sustainability of ecosystem functions and biodiversity. However, quantitative estimates of various disturbance characteristics required in management applications are rare in longer‐term historical studies. Thus, our objectives were to: (1) quantify past disturbance severity, patch size, and stand proportion disturbed, and (2) test for temporal and sub‐regional differences in these characteristics. We developed a comprehensive dendrochronological method to evaluate an approximately two‐century‐long disturbance record in the remaining Central and Eastern European primary mountain spruce forests, where wind and bark beetles are the predominant disturbance agents. We used an unprecedented large‐scale nested design dataset of 541 plots located within 44 stands and 6 sub‐regions. To quantify individual disturbance events, we used tree‐ring proxies, which were aggregated at plot and stand levels by smoothing and detecting peaks in their distributions. The spatial aggregation of disturbance events was used to estimate patch sizes. Data exhibited continuous gradients from low‐ to high‐severity and small‐ to large‐size disturbance events. In addition to the importance of small disturbance events, moderate‐scale (25‐75% of the stand disturbed, >10 ha patch size) and moderate‐severity (25‐75% of canopy disturbed) events were also common. Moderate disturbances represented more than 50% of the total disturbed area and their rotation periods ranged from one to several hundred years, which is within the lifespan of local tree species. Disturbance severities differed among sub‐regions, whereas the stand proportion disturbed varied significantly over time. This indicates partially independent variations among disturbance characteristics. Our quantitative estimates of disturbance severity, patch size, stand proportion disturbed, and associated rotation periods provide rigorous baseline data for future ecological research, decisions within biodiversity conservation, and silviculture intended to maintain native biodiversity and ecosystem functions. These results highlight a need for sufficiently large and adequately connected networks of strict reserves, more complex silvicultural treatments that emulate the natural disturbance spectrum in harvest rotation times, sizes, and intensities, and higher levels of tree and structural legacy retention.
Chapter
A forest stand is a community where the interactions between trees and surroundings, result in a wide range of growth patterns that are also reflected in the stand biomass. The primordial features of stand structure description are structure (even-aged or uneven-aged) and composition (pure or mixed). The variability in structure and composition is high and it is reflected in the variability of growth and biomass as they are influenced by the interactions among individuals, nutrient and water uptake, light absorption, forest microclimate, density and tree distribution in space, and time. Trees’ interactions in forest stands are complex and species traits and proportions are determinant to the growth and biomass patterns. Stand structure determines forest biomass and its sustainability in space and time. Overall it can be said the more diverse stands (mixed) enable higher biomass in space, higher variability in tree’s dimensions (uneven-aged) enable more constant biomass and time, and more complex structures (mixed uneven-aged) can store more biomass in space and time. The biomass sustainability is enhanced by short regeneration periods, by complementarity of species traits, by spatial arrangements promoting complementarity, by silvicultural practices of high frequency and low severity, by maintaining the harvest intensity at a growth resilience level, by the increase of length of the harvest cycles and by the maintenance of, at least, part of the residues to promote the biomass reallocation to the soil.
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Climate change alters forest development pathways, with consequences for ecosystem services and biodiversity. As the rate of warming increases, ecosystem change is expected to accelerate. However, ecosystem dynamics can have many causes unrelated to climate (for example, disturbance and stand development legacies). The compound effects of multiple drivers remain largely unclear. Here, we assessed forest dynamics over 28 years at Berchtesgaden National Park (BGNP), Germany, quantifying the spatiotemporal patterns and unraveling the drivers of forest change. We analyzed high-density forest inventory data, consisting of three consecutive censuses of 3759 permanent sample plots (132,866 tree records in total). We used semi-variograms to analyze spatial patterns of change, and boosted regression trees to quantify the effect of 30 covariates on changes in nine indicators of forest structure and composition. Over the 28 years investigated, the forests of BGNP were becoming denser, structurally more complex, and more species rich. Changes in forest structure were more pronounced and spatially correlated on the landscape than changes in tree species composition. Change rates of all indicators increased over time, signifying an acceleration of forest dynamics since the 1980s. Legacies and climate were the most important drivers of change, but had diverging impacts. Although forest change accelerated with increasing temperature, high legacy levels typical for late development stages dampened it. We here provide evidence for accelerating forest dynamics in mountain forests of the Alps, with potentially far-reaching consequences for biodiversity and ecosystem processes. We highlight that unmanaged forest development toward old-growth conditions could counteract climate-mediated acceleration of forest change. Supplementary information: The online version contains supplementary material available at 10.1007/s10021-021-00674-0.
Chapter
Catastrophic wind disturbances under climatic changes are causing major economic impacts and ecological changes that can persist for decades. Bark beetle (Coleoptera: Curculionidae) population and community dynamics are often linked to such wind disturbances at several spatial and temporal scales ranging from damage to individual trees to large-scale windthrow that may prompt multiyear outbreaks on the landscape scale. In this chapter, we discuss how catastrophic wind disturbances and ensuing biological legacies enhance bark beetle populations, particularly in the context of climatic changes. The high level of variability at the tree, stand, and landscape levels created by windstorms generally has positive consequences for eruptive bark beetle species, particularly in Europe. Poststorm timber salvaging to alleviate pest burdens may push biotic elements, especially those dependent on coarse woody debris and forest gaps, into different successional pathways. Climate change is undoubtedly influencing the interactions between these two major disturbance agents by increasing their intensity and severity levels and altering landscape characteristics with feedback loops. In the Anthropocene, predictive modeling of network interactions between multiple abiotic and biotic disturbances and stressors will be critical for effective mitigation, forest restoration, and sustainable forestry practices in a rapidly changing world.
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Research Highlights: Past disturbances occurred naturally in primary forests in the Southern Carpathians. High-and moderate-severity disturbances shaped the present structure of these ecosystems, which regenerated successfully without forestry interventions. Background and Objectives: Windstorms and bark beetle outbreaks have recently affected large forest areas across the globe, causing concerns that these disturbances lie outside the range of natural variability of forest ecosystems. This often led to salvage logging inside protected areas, one of the main reasons for primary forest loss in Eastern Europe. Although more than two-thirds of temperate primary forests in Europe are located in the Carpathian region of Eastern Europe, knowledge about how natural disturbances shape the forest dynamics in this region is highly essential for future management decisions. Material and Methods: We established our study in a primary forest valley situated in the centre of the largest temperate primary forest landscape in Europe (Făgăras , Mountains). A dendrochronological investigation was carried out to reconstruct the natural disturbance history and relate it to the present forest structure. Results: The dendrochronological analysis revealed high temporal variability in the disturbance patterns both at the patch and stand level. Moderate severity disturbance events were most common (20-40% of canopy disturbed in 60% of the plots) but high severity events did also occur (33% of the plots). Regeneration was spruce-dominated and 71% of the seedlings were found on deadwood microsites. Conclusions: We conclude that the current structure of the studied area is a consequence of the past moderate-severity disturbances and sporadic high-severity events. The peak in disturbances (1880-1910) followed by reduced disturbance rates may contribute to a recent and future increase in disturbances in the Făgăras , Mts. Our findings show that these disturbance types are within the range of natural variability of mountain spruce forests in the Southern Carpathians and should not be a reason for salvage logging in primary forests from this area.
Article
Background Assessing functional diversity to identify its spatial patterns and drivers is an important step towards understanding the adaptive capacity of ecosystems to environmental change. However, until now, these mechanisms were poorly understood in the temperate forests of northeastern China, which prevented the development of new management methods aimed at increasing functional trait diversity and thus ecological resilience. Methods In this study, we mapped functional diversity distributions using a Kriging Interpolation Method. A specific random forest model approach was adopted to test the importance ranking of 18 variables in explaining the spatial variation of functional diversity. Three piecewise structural equation models (pSEMs) with forest types as random effects were constructed for testing the direct effects of climate, and the indirect effects of stand structure on functional diversity across the large study region. Specific causal relationships in each forest type were also examined using 15 linear structural equation models. Results Although environmental filtering by climate is important, stand structure explains most of the functional variation of the forest ecosystems in northeastern China. Our study thus only partially supports the stress-dominance hypothesis. Several abundant species determine most of the functional diversity, which supports the mass ratio hypothesis. Conclusions Our results suggest that forest management aimed at increasing structural complexity can contribute to increased functional diversity, especially regarding the mixing of coniferous and broad-leaved tree species.
Article
The ontogenic forest life cycle of regeneration, maturation, senescence and death is a common starting point for the conceptualization of developmental pathways in forest ecosystems. Nonetheless, the usefulness of this framework under natural stand dynamics in small tree collectives formed by individuals with overlapping and weakly synchronised life cycles is not evident. This research investigated empirical relationships between local structural attributes linked with biomass accumulation, mortality in the canopy zone, the occurrence of undercanopy trees and structural heterogeneity quantified in small spatial scales and compared them with anticipations derived from the theoretical ontogenic life cycle model. The material was collected in six old-growth, mixed-species and mixed-aged forests consisting of European beech (Fagus sylvatica L.), silver fir (Abies alba Mill.) and Norway spruce (Picea abies (L.) H. Karst.) and situated in the central Dinaric Mts. (Bosnia and Herzegovina) and Western Carpathians (southern Poland). In each of the stands, a dense grid of circular plots with a radius of 7 and 15 m was established on an area of about 10 ha, and all live (d1.3 ≥ 7 cm) and dead trees (d1.3 ≥ 20 cm) growing within the plots were registered. The analyses indicated that the relationships between local basal areas of live and dead trees are very weak. Ambiguous relationships between the basal area of live and dead trees and the density of undercanopy trees, the high level of structural heterogeneity in small stand patches, and the tendency towards increasing structural heterogeneity with increasing biomass accumulation suggest that the life cycle model based on the sequence of ontogenic phases is a poor projection of the local developmental pathways in the studied ecosystem. The high level of structural heterogeneity found in small stand patches corroborated the alternative hypothesis that the mortality of canopy trees in most cases releases younger or suppressed individuals with delayed growth and only sporadically leads to the formation of a canopy opening reaching the forest floor. A general framework for an alternative model based on stochastic backward shifts was proposed. It emphasizes the diversity of possible developmental trajectories and assumes that the death of a canopy tree shifts local basal area and frequently also structural heterogeneity backwards on the developmental pathway. Depending on the pre-disturbance situation and the kind of disturbance factor, stochastic backward shifts may lead to different “states” in the space of structural attributes.
Article
The divergent gap characteristics and spatial patterns of canopy gaps created by natural or artificial disturbances can exert a dominant influence on forest structure and composition. However, little research has been conducted on the effects of ice storm damage on canopy gaps in subtropical mature forests of South China. In this study, one semi-natural site was dominated by a broad-leaf forest and two managed sites were representative of plantations with coniferous forests. Based on airborne laser scanning data and field evidence across sites, statistical analyses were used to examine gap characteristics following ice storms of moderate severity. Generalized Ripley’s K-function analysis was applied to test gap spatial patterns at a range of scales, and spatial point pattern analysis was used to quantitate the relative importance of specific influences on patterns of gap occurrence. The results revealed that the average gap size was 75.7 m2 and that 12.2 gaps occurred per hectare. Most gaps were single-tree fall events. In addition to more gaps, the mean gap size was smaller and the shape was more complex in the semi-natural site than in two managed sites. Large differences in gap characteristics were observed among snapped, uprooted, snag, and artificial gap damage types. Gaps generally showed a clustered distribution at large scales (e.g. 70m), whereas spatial patterns varied with gap damage types at different sites. The occurrence of gaps was strongly related to slope and topographic position at the semi-natural site, whereas slope, stem density, and human accessibility (proximity to pathways) were the most important factors affecting gap occurrence at the managed sites. We suggest that gap-based silvicultural treatments and natural disturbances regimes conjoin, highlighting interactions with other factors such as microsite conditions, non-tree vegetation and more.
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The expected future intensification of forest disturbance as a consequence of ongoing anthropogenic climate change highlights the urgent need to more robustly quantify associated biotic responses. Saproxylic beetles are a diverse group of forest invertebrates representing a major component of biodiversity that is associated with the decomposition and cycling of wood nutrients and carbon in forest ecosystems. Disturbance-induced declines or shifts in their diversity indicate the loss of key ecological and/or morphological species traits that could change ecosystem functioning. Functional and phylogenetic diversity of biological communities is commonly used to link species communities to ecosystem functions. However, our knowledge on how disturbance intensity alters functional and phylogenetic diversity of saproxylic beetles is incomplete. Here, we analyzed the main drivers of saproxylic beetle abundance and diversity using a comprehensive dataset from montane primary forests in Europe. We investigated cascading relationships between 250 years of historical disturbance mechanisms, forest structural attributes and the taxonomic, phylogenetic and functional diversity of present-day beetle communities. Our analyses revealed that historical disturbances have significant effects on current beetle communities. Contrary to our expectations, different aspects of beetle communities, that is, abundance, taxonomic, phylogenetic and functional diversity, responded to different disturbance regime components. Past disturbance frequency was the most important component influencing saproxylic beetle communities and habitat via multiple temporal and spatial pathways. The quantity of deadwood and its diameter positively influenced saproxylic beetle abundance and functional diversity, whereas phylogenetic diversity was positively influenced by canopy openness. Analyzing historical disturbances, we observed that current beetle diversity is far from static, such that the importance of various drivers might change during further successional development. Only forest landscapes that are large enough to allow for the full range of temporal and spatial patterns of disturbances and post-disturbance development will enable long-term species coexistence and their associated ecosystem functions.
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Fire is an important disturbance in many forest landscapes, but there is heightened concern regarding recent wildfire activity in western North America. Several regional-scale studies focus on high-severity fire, but a comprehensive examination at all levels of burn severity (i.e., low, moderate, and high) is needed to inform our understanding of the ecological effects of contemporary fires and how they vary among vegetation zones at sub-regional scales. We integrate Landsat time series data with field measurements of tree mortality to map burn severity in forests of the Pacific Northwest, USA, from 1985 to 2010. We then examine temporal trends in fire extent and spatial patterns of burn severity in relation to drought and annual fire extent. Finally, we compare results among vegetation zones and with expectations based on studies of historical landscape dynamics and fire regimes. Small increases in fire extent over time were associated with drought in all vegetation zones, but fire cumulatively affected <3% of wet vegetation zones, and most dry vegetation zones experienced less fire than expectations from fire history studies. Although the proportion of fire at any level of severity did not increase over time, temporal trends toward larger patches of high-severity fire were related to drought and annual fire extent, depending on vegetation zone. In vegetation zones with historically high-severity regimes, high-severity fire accounted for a large proportion of recent fire extent (43–48%) and occurred primarily in patches ≥100 ha. In vegetation zones with historically low- and mixed-severity regimes, low (45–54%)- and moderate-severity (24–36%) fires were prevalent, but proportions of high-severity fire (23–26%), almost half of which occurred in patches ≥100 ha, were much greater than expectations from most fire history studies. Our results support concerns about large patches of high-severity fire in some dry forests but also suggest that spatial patterns of burn severity across much of the extent burned are generally consistent with current understanding of historical landscape dynamics in the region. This study highlights the importance of considering the ecological effects of fire at all levels of severity in management and policy initiatives intended to promote forest biodiversity and resilience to future fire activity.
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The condition of forest ecosystems depends on the temporal and spatial pattern of management interventions and natural disturbances. Remnants of previous conditions persisting after disturbances, or ecosystem legacies, collectively comprise ecosystem memory. Ecosystem memory in turn contributes to resilience and possibilities of ecosystem reorganization following further disturbance. Understanding the role of disturbance and legacies is a prerequisite for maintaining resilience in the face of global change. Several legacy concepts discussed in the peer-reviewed literature, including disturbance, biological, soil, land-use, and silvicultural legacies, overlap in complex ways. Here, we review these established legacy concepts and propose that the new terms “material legacy” (individuals or matter, e.g., survivors, coarse woody debris, nutrients left after disturbance) and “information legacy” (adaptations to historical disturbance regimes) cut across these previous concepts and lead to a new classification of legacies. This includes six categories: material legacies with above- and belowground, and biotic and abiotic categories, and information legacies with above- and belowground categories. These six legacies are influenced by differential patterns of editing and conditioning by “legacy syndromes” that result from natural or human-manipulated disturbance regimes that can be arranged along a gradient of naturalness. This scheme is applied to a case study of hemiboreal forests in the Baltic States of Estonia, Latvia, and Lithuania, where natural disturbance, traditional clearcut silviculture, and afforestation of abandoned agricultural lands constitute the three main legacy syndromes. These legacy syndromes in turn influence forest response to management actions and constrain resilience, leading to a mosaic of natural, manipulated, and artificial (novel) ecosystems across the landscape, depending on how the legacies in each syndrome affect ecological memory.
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Fire frequency is assumed to have exerted a strong influence on historical forest communities in the inland Pacific Northwest. This study reconstructs forest structure and composition in the year 1890 and fire frequency from 1760 to 1890 at 10 sites spanning a broad productivity gradient in the southern Blue Mountains of eastern Oregon. We tested for the relative influence of fire frequency, climate, soils, and topography by fitting variables to ordinations of forest structural and compositional configurations. We also built formal statistical models using non-parametric permutational multivariate analysis of variance. Because fire disturbance and biophysical influences on forest structure and composition may vary depending on the scale at which relationships are examined, we tested the influence of variables at the scale of 4- to 12-ha sites and at the scale of three equal-sized areas within each site. The proportion of fire-intolerant species basal area reconstructed within sites in the year 1890 ranged from 0% to 43%. The proportion of fire-intolerant species basal area reconstructed within equal-sized areas within sites ranged from 0% to 75%. Despite significant differences in historical species composition between and within sites, fire frequencies were relatively similar. Mean fire return intervals (MFRIs) calculated for sites ranged from 10.6 to 21.2 yr. MFRIs calculated for equal-sized areas within sites ranged from 10.6 to 28.8 yr. Fitting fire frequency and biophysical variables to ordinations and model building with perMANOVA showed that topographic position index and vapor pressure deficit had stronger influences on site-scale forest structure and composition than fire frequency metrics. Available soil water was the most important influence on forest structure and composition within equal-sized areas within sites. Relatively frequent fire across a broad range of forest types in the southern Blues appears to have been a relatively uniform influence on forest dynamics modulated by fine-scale biophysical heterogeneity. If return to historical conditions is a goal of management, treatments to reduce fuel and restore frequent fire are appropriate across a broad productivity gradient in the southern Blues.
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