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Secondary tropical forests play an increasingly important role in carbon budgets and biodiversity conservation. Understanding successional trajectories is therefore imperative for guiding forest restoration and climate change mitigation efforts. Forest succession is driven by the demographic strategies-combinations of growth, mortality and recruitment rates-of the tree species in the community. However, our understanding of demographic diversity in tropical tree species stems almost exclusively from old-growth forests. Here, we assembled demographic information from repeated forest inventories along chronosequences in two wet (Costa Rica, Panama) and two dry (Mexico) Neotropical forests to assess whether the ranges of demographic strategies present in a community shift across succession. We calculated demographic rates for >500 tree species while controlling for canopy status to compare demographic diversity (i.e., the ranges of demographic strategies) in early successional (0-30 years), late successional (30-120 years) and old-growth forests using two-dimensional hypervolumes of pairs of demographic rates. Ranges of demographic strategies largely overlapped across successional stages, and early successional stages already covered the full spectrum of demographic strategies found in old-growth forests. An exception was a group of species characterized by exceptionally high mortality rates that was confined to early successional stages in the two wet forests. The range of demographic strategies did not expand with succession. Our results suggest that studies of long-term forest monitoring plots in old-growth forests, from which most of our current understanding of demographic strategies of tropical tree species is derived, are surprisingly representative of demographic diversity in general, but do not replace the need for further studies in secondary forests.

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Forest diversity is the outcome of multiple species-specific processes and tolerances, from regeneration, growth, competition and mortality of trees. Predicting diversity thus requires a comprehensive understanding of those processes. Regeneration processes have traditionally been overlooked, due to high stochasticity and assumptions that recruitment is not limiting for forests. Thus, we investigated the importance of seed production and seedling survival on forest diversity in the Pacific Northwest (PNW) using a forest gap model (ForClim). Equations for regeneration processes were fit to empirical data and added into the model, followed by simulations where regeneration processes and parameter values varied. Adding regeneration processes into ForClim improved the simulation of species composition, compared to Forest Inventory Analysis data. We also found that seed production was not as important as seedling survival, and the time it took for seedlings to grow into saplings was a critical recruitment parameter for accurately capturing tree species diversity in PNW forest stands. However, our simulations considered historical climate only. Due to the sensitivity of seed production and seedling survival to weather, future climate change may alter seed production or seedling survival and future climate change simulations should include these regeneration processes to predict future forest dynamics in the PNW. This article is part of the theme issue 'Ecological novelty and planetary stewardship: biodiversity dynamics in a transforming biosphere'.

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Human actions are causing widespread increases in fire size, frequency, and severity in diverse ecosystems globally. This alteration of fire regimes is considered a threat to numerous animal species, but empirical evidence of how fire regimes are shifting within both threatened species' ranges and protected areas is scarce, particularly at large spatial and temporal scales. We used a big data approach to quantify multidecadal changes in fire regimes in southern Australia from 1980 to 2021, spanning 415 reserves (21.5 million ha) and 129 threatened species' ranges including birds, mammals, reptiles, invertebrates, and frogs. Most reserves and threatened species' ranges within the region have experienced declines in unburnt vegetation (≥30 y without fire), increases in recently burnt vegetation (≤5 y since fire), and increases in fire frequency. The mean percentage of unburnt vegetation within reserves declined from 61 to 36% (1980 to 2021), whereas the mean percentage of recently burnt vegetation increased from 20 to 35%, and mean fire frequency increased by 32%, with the latter two trends primarily driven by the record-breaking 2019 to 2020 fire season. The strongest changes occurred for high-elevation threatened species, and reserves of high elevation, high productivity, and strong rainfall decline, particularly in the southeast of the continent. Our results provide evidence for the widely held but poorly tested assumption that threatened species are experiencing widespread declines in unburnt habitat and increases in fire frequency. This underscores the imperative for developing management strategies that conserve fire-threatened species in an increasingly fiery future.

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Large trees play a vital role in forest carbon stocks, dominating the distribution of community biomass. However, climate change and deforestation are reducing large trees globally, resulting in regional differences in their contribution to carbon stocks. Here, we examined the latitudinal change pattern and drivers of large trees' contributions to stand carbon stocks. Above-ground carbon storage was calculated for 530 plots in old-growth forests across China. Linear regression was used to calculate latitudinal variation in the proportion of above-ground carbon in large trees (i.e., AGC proportion). Variance partitioning and multiple linear regression were used to calculate the relative importance of species diversity, stand structure, functional traits, and environmental factors to AGC proportion. The study found that AGC proportion decreased with increasing latitude, averaging at 64.44 %. Stand structure, particularly the coefficient of variation of DBH, was identified as the key drivers of the AGC proportion. The number of common species (Hill's 1D) had no direct effect on the AGC proportion, while wood density, maximum tree height, and leaf nitrogen-to­phosphorus ratio showed negative effects. The mass-ratio effects on AGC proportion were stronger than diversity effects. Climate variables primarily affected the AGC proportion through stand variables. These results indicate that simultaneously managing high diversity and AGC proportion may pose challenges. Moreover, considering the substantial contribution of large trees to carbon stocks, their storage capacity and sensitivity to environmental changes exert significant control over forest carbon cycles. Therefore, preserving and enhancing the carbon sink function of old-growth forests in the face of climate change and disturbance may depend primarily on protecting existing large trees and soon-to-be large-diameter trees.

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Tree-related Microhabitats (TreMs) are a key structural element having a significant impact on the biodiversity and functioning of forest ecosystems. Although forests enjoying long-term protection host richer and more abundant TreMs compared to managed stands, the quantity and quality of such microstructures in primeval temperate forests are unknown. This study investigates for the first time the assemblage of TreMs in the Bialowieza Forest (BF), which is regarded as the last surviving fragment of pristine lowland forests in the temperate zone of Europe. Relatively undisturbed by human activity since the last glacial period, the BF ecosystem has remained remarkably intact, which may have given rise to its unique TreM assemblage. Here, we show that a primeval forest is characterized by an exceptionally high richness and density of TreMs compared to previously studied natural forests, and that the richness, density and diversity of TreMs are spatially heterogeneous at the micro-scale but homogeneous at the macro-scale. This indicates that adjacent small fragments of habitat (0.05 ha) may have different TreM profiles, but large patches of forest (several ha) host similar assemblages of TreMs. Our profile of TreMs depends on the basal area and density of living trees, the basal area of dead standing trees and the dominance of specific TreM-hosting tree species in a stand. Our study suggests that both the ecological continuity and complexity of a forest supporting many different tree species and the diversity of TreM-forming biota that typically occurs in primeval temperate forests are factors that appear to contribute to the observed profile of TreMs. The results of our study set a benchmark for the quantity and quality of TreMs in broadleaved temperate forests and indicate that the long-term spontaneous natural processes occurring in primeval forests lead to the emergence of ultra-rich, complex assemblages of TreMs.

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Habitat loss is a potential long-term effect of projected climate change for Mediterranean forest ecosystems. Here, we investigated the effectiveness of a close-to-nature silvicultural practice to conserve an old-growth white oak forest patch in Sicily (Italy) and promote regeneration dynamics. The study area, although small, is distinctive for its isolation, position and environmental characteristics. We conducted a Before-After Control-Impact (BACI) study to analyse the responses of different taxonomic groups (vascular plants and birds) to silvicultural treatments (selection thinning, no thinning), and to determine whether close-to-nature silviculture practices may cause significant shifts in the investigated communities. Specifically, we assessed the responses of (1) vascular plants by means of species diversity and taxonomic distinctness indices and (2) birds in terms of diversity, abundance and forest specialisation. Preliminary results suggest that cautious close-to-nature silviculture practice could-by mimicking natural gap dynamics-contribute to maintaining old-growth forest patches and promote oak seedling emergence without short-term detrimental impacts on biodiversity. Although the monitoring has to be repeated over the long-term, the multi-taxon approach and indices incorporating information on taxonomic relationships into diversity measures were demonstrated to be valuable tools for interpreting biotic community structure and dynamics.

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Recently, Zylstra et al. reported that wet sclerophyll forest left unburnt for 75 years experiences a marked decrease in flammability, requiring a radical rethink about fire management. This also highlights the vertical dimension of fires, with species conservation favored by a mosaic of fire types (high pyrodiversity).

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The COVID-19 shutdown has caused a quasi-experimental situation for ecologists in Spring 2020, providing an unprecedented release in acoustic space for avian soundscapes due to the lowest technophony levels experienced for decades. We conducted large-scale passive acoustic monitoring in 68 forest stands during and after the shutdown to compare their acoustic diversity under different management regimes. We designed a before-after sampling scheme of 18 paired stands to evaluate the short-term effect of shutdown on diel and nocturnal acoustic diversity of forest soundscapes. We assessed whether old-growth preserves hosted higher acoustic diversity and vocal activity of flagship specialist birds than production stands during the shutdown, and whether the effect of management was mediated by landscape fragmentation and distance to roads. We derived acoustic richness and vocal activity of flagship specialist birds by systematically performing 15-min long aural listening to identify species vocalizations from all recorded stands. The end of the COVID-19 shutdown led to a rapid decrease in diel and nocturnal biophony and acoustic diversity. During the shutdown, we found significantly higher biophony and acoustic diversity in old-growth preserves than in production stands. Bird acoustic richness and vocalizations of the two most frequent flagship specialists, Dendrocoptes medius and Phylloscopus sibilatrix, were also both higher in old-growth stands. Interestingly, this positive effect of old-growth stands on forest soundscapes suggested that they could potentially attenuate traffic noise, because the distance to roads decreased acoustic diversity and biophony only outside old-growth preserves. Similarly, flagship bird richness increased with old-growth cover in the surrounding landscape while edge density had a negative effect on both acoustic diversity and flagship birds. We suggest that enhancing the old-growth preserve network implemented across French public forests would provide a connected frame of acoustic sanctuaries mitigating the ever-increasing effect of technophony on the acoustic diversity of temperate forest soundscapes.

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Understanding how habitat fragmentation affects individual species is complicated by challenges associated with quantifying species-specific habitat and spatial variability in fragmentation effects within a species' range. We aggregated a 29-year breeding survey data set for the endangered marbled murrelet (Brachyramphus marmoratus) from >42,000 forest sites throughout the Pacific Northwest (Oregon, Washington, and northern California) of the United States. We built a species distribution model (SDM) in which occupied sites were linked with Landsat imagery to quantify murrelet-specific habitat and then used occupancy models to test the hypotheses that fragmentation negatively affects murrelet breeding distribution and that these effects are amplified with distance from the marine foraging habitat toward the edge of the species' nesting range. Murrelet habitat declined in the Pacific Northwest by 20% since 1988, whereas the proportion of habitat comprising edges increased by 17%, indicating increased fragmentation. Furthermore, fragmentation of murrelet habitat at landscape scales (within 2 km of survey stations) negatively affected occupancy of potential breeding sites, and these effects were amplified near the range edge. On the coast, the odds of occupancy decreased by 37% (95% confidence interval [CI] -54 to 12) for each 10% increase in edge habitat (i.e., fragmentation), but at the range edge (88 km inland) these odds decreased by 99% (95% CI 98 to 99). Conversely, odds of murrelet occupancy increased by 31% (95% CI 14 to 52) for each 10% increase in local edge habitat (within 100 m of survey stations). Avoidance of fragmentation at broad scales but use of locally fragmented habitat with reduced quality may help explain the lack of murrelet population recovery. Further, our results emphasize that fragmentation effects can be nuanced, scale dependent, and geographically variable. Awareness of these nuances is critical for developing landscape-level conservation strategies for species experiencing broad-scale habitat loss and fragmentation.

Efectos de la fragmentación sobre las especies en peligro a lo largo de un gradiente desde el interior hasta el borde de su distribución Resumen Es complicado entender el efecto de la fragmentación del hábitat sobre las especies individuales debido a los retos asociados con la cuantificación de hábitats específicos por especie y la variabilidad espacial de los efectos de la fragmentación dentro de la distribución de la especie. Combinamos los datos de un censo reproductivo realizado durante 29 años para el mérgulo jaspeado (Brachyramphus marmoratus) de >42,000 sitios boscosos a lo largo del noroeste del Pacífico (Oregón, Washington, y el norte de California, EE. UU.). Construimos un modelo de distribución de especie (MDE) en el cual los sitios ocupados estuvieron vinculados con imágenes de Landsat para cuantificar el hábitat específico del mérgulo y después usamos los modelos de ocupación para comprobar la hipótesis de que la fragmentación afecta negativamente la distribución reproductiva de la especie y que estos efectos se amplifican con la distancia entre el hábitat de forrajeo marino y el borde de la distribución de anidación de la especie. El hábitat del mérgulo declinó en la zona en un 20% a partir de 1988, mientras que la proporción de hábitat que comprende bordes incrementó en un 17%, lo que indica un aumento en la fragmentación. Además, la fragmentación del hábitat del mérgulo a escala de paisaje (a de 2 km de las estaciones de censo) afectó negativamente a la ocupación de sitios potenciales de reproducción y estos efectos se amplificaron cerca del borde de la distribución. La probabilidad de ocupación disminuyó en un 37% (95% IC -54 a 12) por cada 10% de incremento en el hábitat de borde (es decir, fragmentación) en la costa, pero en el borde de la distribución (88 km tierra adentro), esta probabilidad disminuyó en un 99% (95% IC 98 a 99). De forma contraria, la probabilidad de ocupación incrementó en un 31% (95% IC 14 a 52) por cada 10% de incremento en el hábitat de borde local (a 100 m de las estaciones de censo). La evasión de la fragmentación a gran escala y el uso de hábitats con calidad reducida y fragmentados a nivel local podría explicar la falta de recuperación poblacional del mérgulo. Más allá, nuestros resultados resaltan que los efectos de la fragmentación pueden estar matizados, depender de la escala y tener variación geográfica. Es importante tener conciencia de estos matices para desarrollar estrategias de conservación a nivel paisaje para las especies que experimentan fragmentación y pérdida del hábitat a gran escala.

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Karst made up of limestone is widely considered a "Noah's ark" of biodiversity. Rock and soil substrates comprise two different site types in karst terrain, although both can support dense forests. However, it is unclear whether and how the presence of exposed rock affects forest diversity and tree size. We established a 2.2 ha plot (200 × 110 m) in an old-growth oak forest (> 300 years) in karst terrain in southwestern China. We classified the plot into rock and soil components; we analyzed plant diversity and tree size in each component using species diversity indices (richness, number of individuals, Shannon-Wiener index, and Pielou evenness index), stand spatial structure parameters, diameter at breast height (DBH), tree height (TH), and tree basal area (BA). We also analyzed the distributional patterns of species at the sites using non-metric multidimensional scaling, then assessed the effects of abiotic environmental variables on diversity and tree size using redundancy analysis. Our results indicated that both site types (i.e., rock and soil) had similar overall species diversity; trees and shrubs were largely distributed at random within the study site. Tree size was evenly differentiated in the community, and trees were dominant, particularly on soil. Trees on rock were in a status of medium mixture, whereas shrubs on rock were highly mixed. The opposite trend was observed for trees and shrubs growing on soil. The DBH, TH, and BA were smaller in trees growing on rock than in trees growing on soil. Abiotic environmental variables had varying effects on the diversity and size of trees at the two site types; they only explained 21.76 and 14.30% of total variation, respectively. These results suggest that exposed rock has the effect of reducing tree size, but not diversity, thus highlighting the important role of rock in maintaining diversity; moreover, the results imply that karst microhabitats may mitigate the impacts of topography on tree diversity and growth. Greater attention should be focused on exposed rock in the conservation and management of karst forests and the restoration of degraded forest ecosystems.

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Forest degradation changes the structural heterogeneity of forests and species communities, with potential consequences for ecosystem functions including seed dispersal by frugivorous animals. While the quantity of seed dispersal may be robust towards forest degradation, changes in the effectiveness of seed dispersal through qualitative changes are poorly understood. Here, we carried out extensive field sampling on the structure of forest microhabitats, seed deposition sites and plant recruitment along three characteristics of forest microhabitats (canopy cover, ground vegetation and deadwood) in Europe's last lowland primeval forest (Bialowieza, Poland). We then applied niche modelling to study forest degradation effects on multi-dimensional seed deposition by frugivores and recruitment of fleshy-fruited plants. Forest degradation was shown to (i) reduce the niche volume of forest microhabitat characteristics by half, (ii) homogenize the spatial seed deposition within and among frugivore species, and (iii) limit the regeneration of plants via changes in seed deposition and recruitment. Our study shows that the loss of frugivores in degraded forests is accompanied by a reduction in the complementarity and quality of seed dispersal by remaining frugivores. By contrast, structure-rich habitats, such as old-growth forests, safeguard the diversity of species interactions, forming the basis for high-quality ecosystem functions.

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Conventional conservation policies in Europe notably rely on the passive restoration of natural forest dynamics by setting aside forest areas to preserve forest biodiversity. However, since forest reserves cover only a small proportion of the territory, conservation policies also require complementary conservation efforts in managed forests in order to achieve the biodiversity targets set up in the Convention on Biological Diversity. Conservation measures also raise the question of large herbivore management in and around set-asides, particularly regarding their impact on understory vegetation. Although many studies have separately analyzed the effects of forest management, management abandonment, and ungulate pressure on forest biodiversity, their joint effects have rarely been studied in a correlative framework. We studied 212 plots located in 15 strict forest reserves paired with adjacent managed forests in European France. We applied structural equation models to test the effects of management abandonment, stand structure, and ungulate pressure on the abundance, species richness, and diversity of herbaceous vascular plants and terricolous bryophytes. We showed that stand structure indices and plot-level browsing pressure had direct and opposite effects on herbaceous vascular plant species diversity; these effects were linked with the light tolerance of the different species groups. Increasing canopy cover had an overall negative effect on herbaceous vascular plant abundance and species diversity. The effect was two to three times greater in magnitude than the positive effects of browsing pressure on herbaceous plants diversity. On the other hand, a high stand density index had a positive effect on the species richness and diversity of bryophytes, while browsing had no effect. Forest management abandonment had few direct effects on understory plant communities, and mainly indirectly affected herbaceous vascular plant and bryophyte abundance and species richness and diversity through changes in vertical stand structure. Our results show that conservation biologists should rely on foresters and hunters to lead the preservation of understory vegetation communities in managed forests since, respectively, they manipulate stand structure and regulate ungulate pressure. Their management actions should be adapted to the taxa at stake, since bryophytes and vascular plants respond differently to stand and ungulate factors.

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Tree-related microhabitats (TreMs) are among the most important structural components of a forest, and have a significant impact on biodiversity and influence ecosystem functioning. Although forests that depend on natural lowland water regimes are severely endangered worldwide, and floodplain forests are considered to be the most complex and biologically rich habitats in the temperate zone, the TreMs in them have yet to be identified. This study investigates the assemblage of TreMs in natural Willow-Poplar riparian forests and analyses the environmental factors that influence their qualitative and quantitative compositions. A total of 90 sample plots (0.05 ha each) were selected at random in old-growth riparian forests that occur along a large unregulated river, the Vistula (Poland). A total of 62 TreM types were identified with a mean number of 16.0 ± 4.6 SD TreM types per plot and a mean density of 829.4 ± 360.1 SD TreM-bearing trees ha-1. The number of TreMs found on an individual tree depends on its diameter, the number of trunks, its living status (living vs. dead tree) and the species it belongs to. The richness, density and diversity of TreMs found on a plot depends on the density of living trees, the basal area of living or dead trees, the number of tree species, and the percentage of Willows Salix sp. or of multi-trunk trees. Our study records for the first time the assemblage of TreMs in natural Willow-Poplar riparian forests and provides a reference for floodplain habitats. The results indicate that multi-species forests influenced by natural waterflow-related disturbances are hot-spots of TreM richness and abundance, and highlight the urgent need for the protection or restoration of these vanishing habitats.

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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.

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 post­perturbation 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 post­perturbation 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 sous­étage 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.

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Forest fires can cause great changes in the composition, structure and functioning of forest ecosystems. We studied the effects of a fire that occurred >50 years ago in a temperate rainforest that caused flooding conditions in a Placic Andosol to evaluate how long these effects last; we hypothesized that the effects of fire on the soil greenhouse gas (GHG) balance could last for many years. We made monthly measurements of fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) during two years of soils in an unburned forest (UF) and a nearby site that burned >50 years ago (BS). Our results show that CO2 emissions from soils were higher in the UF than in the BS, and positively correlated with temperature and negatively with soil water content at both sites. Both sites were net CH4 sinks (higher in the UF) and fluxes correlated positively with soil water content and negatively with temperature (stronger relation in the BS). Emissions of N2O were low at both sites and showed correlation with friction velocity at the UF site. The soil GHG balance showed that the UF emitted about 80% more than the BS (5079 ± 1772 and 2815 ± 1447 g CO2-eq m-2 y-1, respectively). Combining our measured fluxes with data of CO2 net ecosystem exchange, we estimated that at the ecosystem level, the UF was a GHG sink while the BS was a source, showing a long-lasting effect of the fire and the importance of preserving these forest ecosystems.

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BACKGROUND AND AIMS: Nutrient resorption from senescing tissue is a key mechanism for plants to conserve nutrients, and can affect the nutrient dynamics of ecosystems. Yet, our limited knowledge of nitrogen (N) resorption and release from mosses hampers our understanding of the role of mosses as N sources and, thereby, N cycling in moss-dominated ecosystems. The aims of this study were to estimate N resorption efficiency (NRE) of two moss species, identify the pathways of N release from the mosses and to provide a better understanding of N cycling and budgeting strategies of mosses. METHODS: The dynamics of N allocation along annual moss segments of two dominant moss species (Actinothuidium hookeri and Hylocomium splendens) were assessed in old-growth fir forests using an in situ15N tracer experiment. KEY RESULTS: The NRE of A. hookeri and H. splendens was 61 and 52 %, respectively. While the mosses lost 23 and 33 % N from live tissues via leaching, 15 and 14 % of N remained in senesced tissues (>3 years old) in A. hookeri and H. splendens, respectively. CONCLUSIONS: Both mosses resorbed the majority of their tissue N, but a considerable amount of N was lost from live segments. Our results highlight the crucial role mosses play as N sinks in ecosystems, since N retention (resorbed and sequestered in senescent tissue) outweighed N loss via leaching. However, the sink strength depends on temperature and precipitation, which will change in a future climate. The values for NRE, leaching, etc. estimated here can help improve biogeochemical models aiming to complete N budgets for moss-abundant ecosystems.

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The natural range of variation (NRV) is an important reference for ecosystem management, but has been scarcely quantified for forest landscapes driven by infrequent, severe disturbances. Extreme events such as large, stand-replacing wildfires at multi-century intervals are typical for these regimes; however, data on their characteristics are inherently scarce, and, for land management, these events are commonly considered too large and unpredictable to integrate into planning efforts (the proverbial "Black Swan"). Here, we estimate the NRV of late-seral (mature/old-growth) and early-seral (post-disturbance, pre-canopy-closure) conditions in a forest landscape driven by episodic, large, stand-replacing wildfires: the Western Cascade Range of Washington, USA (2.7 million ha). These two seral stages are focal points for conservation and restoration objectives in many regions. Using a state-and-transition simulation approach incorporating uncertainty, we assess the degree to which NRV estimates differ under a broad range of literature-derived inputs regarding (1) overall fire rotations and (2) how fire area is distributed through time, as relatively frequent smaller events (less episodic), or fewer but larger events (more episodic). All combinations of literature-derived fire rotations and temporal distributions (i.e., "scenarios") indicate that the largest wildfire events (or episodes) burned up to 105 -106  ha. Under most scenarios, wildfire dynamics produced 5th-95th percentile ranges for late-seral forests of ~47-90% of the region (median 70%), with structurally complex early-seral conditions composing ~1-30% (median 6%). Fire rotation was the main determinant of NRV, but temporal distribution was also important, with more episodic (temporally clustered) fire yielding wider NRV. In smaller landscapes (20,000 ha; typical of conservation reserves and management districts), ranges were 0-100% because fires commonly exceeded the landscape size. Current conditions are outside the estimated NRV, with the majority of the region instead covered by dense mid-seral forests (i.e., a regional landscape with no historical analog). Broad consistency in NRV estimates among widely varied fire regime parameters suggests these ranges are likely relevant even under changing climatic conditions, both historical and future. These results indicate management-relevant NRV estimates can be derived for seral stages of interest in extreme-event landscapes, even when incorporating inherent uncertainties in disturbance regimes.

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Slow ecological processes challenge conservation. Short-term variability can obscure the importance of slower processes that may ultimately determine the state of a system. Furthermore, management actions with slow responses can be hard to justify. One response to slow processes is to explicitly concentrate analysis on state dynamics. Here, we focus on identifying drivers of Northern Spotted Owl (Strix occidentalis caurina) territorial occupancy dynamics across 11 study areas spanning their geographic range and forecasting response to potential management actions. Competition with Barred Owls (Strix varia) has increased Spotted Owl territory extinction probabilities across all study areas and driven recent declines in Spotted Owl populations. Without management intervention, the Northern Spotted Owl subspecies will be extirpated from parts of its current range within decades. In the short term, Barred Owl removal can be effective. Over longer time spans, however, maintaining or improving habitat conditions can help promote the persistence of northern spotted owl populations. In most study areas, habitat effects on expected Northern Spotted Owl territorial occupancy are actually greater than the effects of competition from Barred Owls. This study suggests how intensive management actions (removal of a competitor) with rapid results can complement a slower management action (i.e., promoting forest succession).

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BACKGROUND: Southern Appalachian forests are dominated by second-growth vegetation following decades of intensive forestry and agricultural use, although some old-growth patches remain. While it's been shown that second-growth areas may exhibit comparable species richness to old-growth in the area, the extent to which populations of arthropods in second-growth areas have persisted vs. recolonized from other areas remains unexamined. The implications for conservation of both classes of forest are significant. Here we analyze population diversity and relatedness across five old-growth and five second-growth populations of flightless, leaf litter-inhabiting beetles in the genus Eurhoptus (Coleoptera: Curculionidae: Cryptorhynchinae). Our main goal is asking whether second-growth areas show diminished diversity and/or signals of recolonization from old-growth sources. RESULTS: Population genetic and phylogenetic analyses do not reveal any consistent differences in diversity between the old-growth and second-growth populations examined. Some second-growth populations retain substantial genetic diversity, while some old-growth populations appear relatively depauperate. There is no phylogenetic indication that second-growth populations have recolonized from old-growth source populations. CONCLUSIONS: Most populations contain substantial and unique genetic diversity indicating long-term persistence in the majority of sites. The results support substantial resilience in second-growth populations, though the geographic scale of sampling may have hindered detection of recolonization patterns. Broad scale phylogeographic patterns reveal a deep break across the French Broad River basin, as has been reported in several other taxa of limited dispersal abilities. In Eurhoptus this break dates to ~ 2-6 Ma ago, on the older end of the range of previously estimated dates.

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