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Although climate change is expected to drive tree species toward colder and wetter regions of their distribution, broadscale empirical evidence is lacking. One possibility is that past and present human activities in forests obscure or alter the effects of climate. Here, using data from more than two million monitored trees from 73 widely distributed species, we quantify changes in tree species density within their climatic niches across Northern Hemisphere forests. We observe a reduction in mean density across species, coupled with a tendency toward increasing tree size. However, the direction and magnitude of changes in density exhibit considerable variability between species, influenced by stand development that results from previous stand-level disturbances. Remarkably, when accounting for stand development, our findings show a significant change in density toward cold and wet climatic conditions for 43% of the species, compared to only 14% of species significantly changing their density toward warm and arid conditions in both early-and late-development stands. The observed changes in climate-driven density showed no clear association with species traits related to drought tolerance, recruitment and dispersal capacity, or resource use, nor with the temperature or aridity affiliation of the species, leaving the underlying mechanism uncertain. Forest conservation policies and associated management strategies might want to consider anticipated long-term species range shifts alongside the integration of contemporary within-distribution density changes. [ABSTRACT FROM AUTHOR]

Climate change effects on tree reproduction are poorly understood, even though the resilience of populations relies on sufficient regeneration to balance increasing rates of mortality. Forest‐forming tree species often mast, i.e. reproduce through synchronised year‐to‐year variation in seed production, which improves pollination and reduces seed predation. Recent observations in European beech show, however, that current climate change can dampen interannual variation and synchrony of seed production and that this masting breakdown drastically reduces the viability of seed crops. Importantly, it is unclear under which conditions masting breakdown occurs and how widespread breakdown is in this pan‐European species. Here, we analysed 50 long‐term datasets of population‐level seed production, sampled across the distribution of European beech, and identified increasing summer temperatures as the general driver of masting breakdown. Specifically, increases in site‐specific mean maximum temperatures during June and July were observed across most of the species range, while the interannual variability of population‐level seed production (CVp) decreased. The declines in CVp were greatest, where temperatures increased most rapidly. Additionally, the occurrence of crop failures and low seed years has decreased during the last four decades, signalling altered starvation effects of masting on seed predators. Notably, CVp did not vary among sites according to site mean summer temperature. Instead, masting breakdown occurs in response to warming local temperatures (i.e. increasing relative temperatures), such that the risk is not restricted to populations growing in warm average conditions. As lowered CVp can reduce viable seed production despite the overall increase in seed count, our results warn that a covert mechanism is underway that may hinder the regeneration potential of European beech under climate change, with great potential to alter forest functioning and community dynamics. [ABSTRACT FROM AUTHOR]

Key message: In European mountain forests, the growth of silver fir (Abies alba Mill.), sycamore maple (Acer pseudoplatanus L.), European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) H. Karst.) seedlings is more strongly affected by ungulate browsing than by elevation. But, the constraint exerted by ungulates, in particular the probability for seedlings to be browsed, increases with elevation for most species. Context: While concerns about mountain forest regeneration rise due to their high vulnerability to climate change, the increase in wild ungulate populations and the expansion of their range in the last decades exert an additional constraint on the survival and growth of young trees. Understanding how this constraint can vary with elevation is thus a key to assess the consequences of this population increase for the regeneration of mountain forests. Aims: In this study, we investigate the effect of elevation on (i) the occurrence of browsing for seedlings and on (ii) the reduction in seedling growth induced by ungulate browsing. Methods: We monitored height growth and browsing occurrence on silver fir, sycamore maple, European beech and Norway spruce seedlings across seven elevation gradients (from 400 to 2013 m) located from France to northern Sweden. Results: Seedlings of the two most palatable species—fir and maple—were more likely to be browsed at high elevation while the opposite effect was observed for spruce. Browsing strongly reduced seedling growth for all species but Norway spruce, while elevation had no direct effect on seedling growth. This browsing-induced growth reduction was stronger at high elevation for fir seedlings. Conclusions: Browsing is overall a stronger constraint on seedling growth than elevation for four dominant species of European mountain forests. Elevation can, however, affect both browsing probability and the effect of browsing on seedling growth. Our results highlight the importance of taking into account ungulate pressure and its interactive effect with elevation when forecasting the regeneration of mountain forests under a changing climate. [ABSTRACT FROM AUTHOR]

Tree species composition is known to influence forest productivity, but its effect on forest resilience to disturbances such as storms remains largely unexplored. Furthermore, climate is likely to influence forest resilience directly but also to influence the effect of tree species composition on resilience. In Europe, storm‐induced tree mortality is currently increasing across all climatic biomes. Understanding the drivers of forest resilience to storms and its consistency across climates appears to be crucial for predicting the consequences of climate change for European forests.In this study, we used a simulation approach with an integral projection model calibrated with National Forest Inventory (NFI) data at the European scale. We restricted our simulations to tree species assemblages observed in the NFI data, covering a species diversity gradient nested within a climate gradient. We quantified functional diversity and the mean position of each species assemblage at equilibrium on two functional axis: (i) conservative versus fast growing and (ii) low versus high recruitment. We disturbed each species assemblage from equilibrium using species‐specific storm disturbance mortality probabilities and quantified the assemblages' resistance (inverse of immediate basal area loss), recovery (slope of post‐disturbance increase in basal area) and resilience (inverse of the cumulative deviation of basal area from the undisturbed state).We found that on average, species‐rich assemblages had higher recovery and resilience to storm disturbance, while functional diversity improved resistance and recovery. When analysing how this effect varied with climate, we found that diversity significantly increased resistance and resilience in the climatic margins only. Finally, we found that storm resilience was also driven by species mean position along both functional axes. In particular, the conservative‐productive axis had an effect two to three times greater than diversity: forests dominated by conservative species were more resistant and resilient, but had lower recovery than species assemblages dominated by fast‐growing species.Taken together, these results show that climate and tree species composition interact to control the ability of forests to resist and recover from a storm disturbance through both direct and indirect effects. As such, our findings should help to better anticipate climate change consequences for forest ecosystems. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Key message: Metabarcoding analysis of soil fungal communities in French mountain forests revealed that harvesting intensity, time since last harvest and former land use had no effect on fungal community composition compared to key abiotic factors. Low-intensity management in these uneven-aged mountain forests therefore has limited effects on soil fungal community composition which is mainly driven by elevation and edaphic properties. Context: Past and current human activities are known to affect forest biodiversity. However, the effects of former land use and forest management have been studied much more extensively on higher plants than on fungi. Aims: Our objectives were to assess the effects of harvesting intensity, duration since last harvest and former land use on soil fungal communities in uneven-aged mountain high forests. Methods: On the basis of historical land-use maps drawn between 1862 and 1864 and on historical forest management archives, we selected 62 sites in the French Alps with contrasting land-use histories (ancient forests, which were already forested on historical maps vs recent forests, which have recovered following abandonment of pastures) and different durations since last harvest (from 1 to over 50 years). We carried out soil sampling and assessed fungal diversity by metabarcoding analysis. We analysed soil fungal molecular operational taxonomic units (MOTU) diversity as a whole and for the main lifestyle groups (such as wood saprotrophic or ectomycorrhizal fungi) using multiple linear regressions on Shannon’s diversity index and fungal taxonomic composition using canonical correlation analysis. Results: We found no significant effect of harvesting intensity, time since last harvest or land-use history on total fungal MOTU diversity, fungal lifestyle diversity or taxonomic composition. In contrast, we observed significant effects of elevation, pH, organic carbon and available phosphorus content on the taxonomic and functional composition of soil fungal communities. Conclusions: The structure of soil fungal communities (i.e. diversity and species composition) was mainly determined by elevation and edaphic factors, indicating a high-context dependency, as previously found in similar studies. Our study in mountain forests shows that recent forests established on former pastures had no legacy effect on soil conditions and fungal communities, in contrast to previous results in lowland areas, where recent forests were mainly established on former cropland. Uneven-aged forest management had no effect on fungal diversity, in contrast to previous results observed in even-aged high forests. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ecology is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Summary: The periodic production of large seed crops, or masting, is a widespread phenomenon in perennial plants. This behavior can enhance the reproductive efficiency of plants, leading to increased fitness, and produce ripple effects on food webs. While variability from year to year is a defining characteristic of masting, the methods used to quantify this variability are highly debated. The commonly used coefficient of variation lacks the ability to account for the serial dependence in mast data and can be influenced by zeros, making it a less suitable choice for various applications based on individual‐level observations, such as phenotypic selection, heritability, and climate change studies, which rely on individual‐plant‐level datasets that often contain numerous zeros. To address these limitations, we present three case studies and introduce volatility and periodicity, which account for the variance in the frequency domain by emphasizing the significance of long intervals in masting. By utilizing examples of Sorbus aucuparia, Pinus pinea, Quercus robur, Quercus pubescens, and Fagus sylvatica, we demonstrate how volatility captures the effects of variance at both high and low frequencies, even in the presence of zeros, leading to improved ecological interpretations of the results. The growing availability of long‐term, individual‐plant datasets promises significant advancements in the field, but requires appropriate tools for analysis, which the new metrics provide. [ABSTRACT FROM AUTHOR]

In forest communities, light competition is a key process for community assembly. Species' differences in seedling and sapling tolerance to shade cast by overstory trees is thought to determine species composition at late‐successional stages. Most forests are distant from these late‐successional equilibria, impeding a formal evaluation of their potential species composition. To extrapolate competitive equilibria from short‐term data, we therefore introduce the JAB model, a parsimonious dynamic model with interacting size‐structured populations, which focuses on sapling demography including the tolerance to overstory competition. We apply the JAB model to a two‐"species" system from temperate European forests, that is, the shade‐tolerant species Fagus sylvatica L. and the group of all other competing species. Using Bayesian calibration with prior information from external Slovakian national forest inventory (NFI) data, we fit the JAB model to short time series from the German NFI. We use the posterior estimates of demographic rates to extrapolate that F. sylvatica will be the predominant species in 94% of the competitive equilibria, despite only predominating in 24% of the initial states. We further simulate counterfactual equilibria with parameters switched between species to assess the role of different demographic processes for competitive equilibria. These simulations confirm the hypothesis that the higher shade tolerance of F. sylvatica saplings is key for its long‐term predominance. Our results highlight the importance of demographic differences in early life stages for tree species assembly in forest communities. [ABSTRACT FROM AUTHOR]

With climate change, natural disturbances such as storm or fire are reshuffled, inducing pervasive shifts in forest dynamics. To predict how it will impact forest structure and composition, it is crucial to understand how tree species differ in their sensitivity to disturbances. In this study, we investigated how functional traits and species mean climate affect their sensitivity to disturbances while controlling for tree size and stand structure. With data on 130,594 trees located on 7617 plots that were disturbed by storm, fire, snow, biotic or other disturbances from the French, Spanish, and Finnish National Forest Inventory, we modeled annual mortality probability for 40 European tree species as a function of tree size, dominance status, disturbance type, and intensity. We tested the correlation of our estimated species probability of disturbance mortality with their traits and their mean climate niches. We found that different trait combinations controlled species sensitivity to disturbances. Storm-sensitive species had a high height-dbh ratio, low wood density and high maximum growth, while fire-sensitive species had low bark thickness and high P50. Species from warmer and drier climates, where fires are more frequent, were more resistant to fire. The ranking in disturbance sensitivity between species was overall consistent across disturbance types. Productive conifer species were the most disturbance sensitive, while Mediterranean oaks were the least disturbance sensitive. Our study identified key relations between species functional traits and disturbance sensitivity, that allows more reliable predictions of how changing climate and disturbance regimes will impact future forest structure and species composition at large spatial scales. [ABSTRACT FROM AUTHOR]

Aim: Linking local population dynamics and species distributions is crucial to predicting the impacts of climate change. Although many studies focus on the mean fitness of populations, theory shows that species distributions can be shaped by demographic stochasticity or population resilience. Here, we examine how mean fitness (measured by invasion rate), demographic stochasticity and resilience (measured by the ability to recover from disturbance) constrain populations at the edges compared with the climatic centre. Location: Europe: Spain, France, Germany, Finland and Sweden. Period: Forest inventory data used for fitting the models cover the period from 1985 to 2013. Major taxa Dominant European tree species; angiosperms and gymnosperms. Methods: We developed dynamic population models covering the entire life cycle of 25 European tree species with climatically dependent recruitment models fitted to forest inventory data. We then ran simulations using integral projection and individual‐based models to test how invasion rates, risk of stochastic extinction and ability to recover from stochastic disturbances differ between the centre and edges of the climatic niches of species. Results: Results varied among species, but in general, demographic constraints were stronger at warm edges and for species in harsher climates. Conversely, recovery was more limiting at cold edges. In addition, we found that for several species, constraints at the edges were attributable to demographic stochasticity and capacity for recovery rather than mean fitness. Main conclusions Our results highlight that mean fitness is not the only mechanism at play at the edges; demographic stochasticity and population capacity to recover also matter for European tree species. To understand how climate change will drive species range shifts, future studies will need to analyse the interplay between population mean growth rate and stochastic demographic processes in addition to disturbances. [ABSTRACT FROM AUTHOR]

Question: Differences in understorey vegetation between ancient and recent forests have been thoroughly explored; however, few studies have investigated the legacies of different former land uses in recent forests. Indeed, due to more intense agricultural practices (tillage and fertilisation), legacy effects are expected to be stronger in former cropland or meadows than in former pastures. Our objectives were to compare soil conditions, taxonomic composition and functional composition of understorey plant communities in recent forests located on former pastures, meadows or cropland, with ancient forests as a reference. Location: Tarentaise Valley, Savoy, France. Methods: Based on land‐use maps surveyed between 1862 and 1864, we selected 82 forest sites with different former land uses in mountain forests in the French Alps and carried out soil sampling and botanical surveys. To account for potential confounding factors (altitude, canopy cover, tree species composition), we applied multiple linear regressions to analyse soil properties, canonical correspondence analysis to analyse plant taxonomic composition and multispecies generalised linear mixed‐effects models to analyse relationships between plant functional composition and former land uses. Results: The soils of former cropland were richer in nutrients and more alkaline compared to other past land uses, while soils on former pastures and meadows differed only slightly from ancient forests. Ancient forests were characterised by acidophilic, shade‐tolerant, low‐stature, forest‐dependent species, whereas former cropland was characterised by calcicolous non‐forest species. Former pasture and meadow communities displayed a distinct taxonomic composition compared to other past land uses, but a functional composition closer to ancient forest than to former cropland. Conclusion: Former cropland has a stronger legacy effect than former pastures or meadows. This could explain small differences between ancient and recent forests observed in previous studies conducted in mountain landscapes where former cropland was rare. [ABSTRACT FROM AUTHOR]

Recent climate warming has fueled interest into climate‐driven range shifts of tree species. A common approach to detect range shifts is to compare the divergent occurrences between juvenile and adult trees along environmental gradients using static data. Divergent occurrences between life stages can, however, also be caused by ontogenetic effects. These include shifts of the viable environmental conditions throughout development ('ontogenetic niche shift') as well as demographic dependencies that constrain the possible occurrence of subsequent life stages. Whether ontogenetic effects are an important driver of divergent occurrences between juvenile and adult trees along large‐scale climatic gradients is largely unknown. It is, however, critical in evaluating whether impacts of environmental change can be inferred from static data on life stage occurrences. Here, we first show theoretically, using a two‐life stage simulation model, how both temporal range shift and ontogenetic effects can lead to similar divergent occurrences between adults and juveniles (juvenile divergence). We further demonstrate that juvenile divergence can unambiguously be attributed to ontogenetic effects, when juveniles diverge from adults in opposite direction to their temporal shift along the environmental gradient. Second, to empirically test whether ontogenetic effects are an important driver of divergent occurrences across Europe, we use repeated national forest inventories from Sweden, Germany and Spain to assess juvenile divergence and temporal shift for 40 tree species along large‐scale climatic gradients. About half of the species‐country combinations had significant juvenile divergences along heat sum and water availability gradients. Only a quarter of the tree species had significant detectable temporal shifts within the observation period. Furthermore, significant juvenile divergences were frequently associated with opposite temporal shifts, indicating that ontogenetic effects are a relevant cause of divergent occurrences between life stages. Our study furthers the understanding of ontogenetic effects and challenges the practice of inferring climate change impacts from static data. [ABSTRACT FROM AUTHOR]

Aim: The population processes that drive tree species distribution are still widely debated. We test the hypotheses that metapopulation processes of colonization and extinction are linked to predictions of species distribution models. Location: Europe: Spain, France, Germany, Finland and Sweden. Taxon: Angiosperms and Gymnosperms. Methods: For 17 tree species analysed, we fitted species distribution models (SDM) relating environmental variables to presence–absence data across Europe. Then, using independent data from national forest inventories across Europe, we tested whether colonization and extinction probabilities are related to SDM occurrence probabilities. Finally, we assessed the probability of presence at metapopulation equilibrium depending on colonization and extinction probabilities. Results: We found that for most species at least one process (colonization/extinction) is related to SDM occurrence probability, but rarely both (only two species). Depending on the species, the link was either for colonization or for extinction, but relationships were generally weak. In addition, the metapopulation models tended to overestimate the occurrence probability at equilibrium. Main conclusions: Our study shows that metapopulation processes are only weakly related to SDM occurrence probability and call for caution in extrapolating SDM models to metapopulation dynamics. [ABSTRACT FROM AUTHOR]

In community ecology, it is widely assumed that organisms with similar traits compete more intensely with one another for resources. This assumption is often encoded into theory and empirical tests via a unimodal competition function, which predicts that per capita competitive effect declines with separation in traits. Yet it remains unknown how well this function represents the true effect of traits on competitive outcomes, especially for long-lived plant communities, where lifetime fitness is difficult to estimate. Here, we evaluate the shape of competition functions embedded in two resource-based (RB) models, wherein plants compete for shared, essential resources. In the first RB model individuals compete for two essential nutrients, and in the second they compete for light in a size-based successional setting. We compared the shapes of the competition functions that emerged from interactions within these RB models to the unimodal function and others shapes commonly applied. In few instances did the trait-based competition function emerging from the RB model even vaguely resemble any of the shapes previously used. The mismatch between these two approaches suggests that theory derived using fixed competition functions based on trait separation may not apply well to plant systems, where individuals compete for shared resources. The more promising path will be to model depletion of resources by populations in relation to their traits, with its consequences for fitness landscapes and competitive exclusion. [ABSTRACT FROM AUTHOR]

This document is a correction notice for an article titled "Forest management and former land use have no effect on soil fungal diversity in uneven-aged mountain high forests." The correction addresses an error in the author name of Georges Kunstler, where it was originally spelled as "Georges Kunsler." The correct spelling of the author's name is "Georges Kunstler." The correction has been made to the author group and the original article. The document provides the correct author names as Sylvain Mollier, Georges Kunstler, Jean-Luc Dupouey, Stephen Mulero, and Laurent Bergès. [Extracted from the article]

There is an urgent need to synthesize the state of our knowledge on plant responses to climate. The availability of open-access data provide opportunities to examine quantitative generalizations regarding which biomes and species are most responsive to climate drivers. Here, we synthesize time series of structured population models from 162 populations of 62 plants, mostly herbaceous species from temperate biomes, to link plant population growth rates (λ) to precipitation and temperature drivers. We expect: (1) more pronounced demographic responses to precipitation than temperature, especially in arid biomes; and (2) a higher climate sensitivity in short-lived rather than long-lived species. We find that precipitation anomalies have a nearly three-fold larger effect on λ than temperature. Species with shorter generation time have much stronger absolute responses to climate anomalies. We conclude that key species-level traits can predict plant population responses to climate, and discuss the relevance of this generalization for conservation planning. Plant population growth rate is sensitive to annual temperature and precipitation anomalies. Here the authors analyse time series of population projection models from multiple biomes, finding a relationship between short generation times and strong demographic responses to climate—particularly precipitation—anomalies. [ABSTRACT FROM AUTHOR]

Species range limits are thought to result from a decline in demographic performance at range edges. However, recent studies reporting contradictory patterns in species demographic performance at their edges cast doubt on our ability to predict climate change demographic impacts. To understand these inconsistent demographic responses, we need to shift the focus from geographic to climatic edges and analyse how species responses vary with climatic constraints at the edge and species' ecological strategy.Here we parameterised integral projection models with climate and competition effects for 27 tree species using forest inventory data from over 90,000 plots across Europe. Our models estimate size‐dependent climatic responses and evaluate their effects on two life trajectory metrics: life span and passage time—the time to grow to a large size. Then we predicted growth, survival, life span and passage time at the hot and dry or cold and wet edges and compared them to their values at the species climatic centre to derive indices of demographic response at the edge. Using these indices, we investigated whether differences in species demographic response between hot and cold edges could be explained by their position along the climate gradient and functional traits related to their climate stress tolerance.We found that at cold and wet edges of European tree species, growth and passage time were constrained, whereas at their hot and dry edges, survival and life span were constrained. Demographic constraints at the edge were stronger for species occurring in extreme conditions, that is, in hot edges of hot‐distributed species and cold edges of cold‐distributed species. Species leaf nitrogen content was strongly linked to their demographic responses at the edge. In contrast, we found only weak links with wood density, leaf size and xylem vulnerability to embolism.Synthesis. Our study presents a more complicated picture than previously thought with demographic responses that differ between hot and cold edges. Predictions of climate change impacts should be refined to include edge and species characteristics. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ecology is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

For decades, ecologists have investigated the effects of tree species diversity on tree productivity at different scales and with different approaches ranging from observational to experimental study designs. Using data from five European national forest inventories (16,773 plots), six tree species diversity experiments (584 plots), and six networks of comparative plots (169 plots), we tested whether tree species growth responses to species mixing are consistent and therefore transferrable between those different research approaches. Our results confirm the general positive effect of tree species mixing on species growth (16% on average) but we found no consistency in species‐specific responses to mixing between any of the three approaches, even after restricting comparisons to only those plots that shared similar mixtures compositions and forest types. These findings highlight the necessity to consider results from different research approaches when selecting species mixtures that should maximize positive forest biodiversity and functioning relationships. [ABSTRACT FROM AUTHOR]

Context Positive diversity–productivity relationships have been reported in different plant communities, including tree communities. These effects may be strongly related to both structural diversity and functional diversity, but also to their interactions if there is a non-random distribution of species functional characteristics among canopy layers. Aims We explore the relative effects on forest productivity of tree species diversity, tree size inequality, and species shade tolerance diversity, as well as the effect of the distribution of tree shade tolerance in the canopy. Methods We used 11,054 mixed-species forest plots from the French Forest Inventory (IGN) distributed throughout France (2006–2011). We analyzed the effects of species richness, shade tolerance diversity, and height inequality on forest plot productivity, represented by basal area annual increment over a period of 5 years, while controlling for first-order structure characteristics (basal area and quadratic mean diameter) and environmental factors (soil water budget and sum of growing degree days). Using the covariance between tree height and shade tolerance in mixed species canopies, we also explored the effect of the distribution of species’ shade tolerance among canopy layers. Results The results showed a positive effect of species richness (effect size, 0.02) and a negative effect of height inequality (− 0.05) on mixed-forest productivity. We also showed that a negative covariance between shade tolerance and height (e.g., higher proportion of shade-tolerant species in lower height classes) increased productivity (0.01). Shade tolerance diversity did not affect productivity. Conclusion In tree communities, as shown previously in monospecific forest stands, tree size inequality reduces productivity. This effect is modulated by the distribution of shade tolerance among canopy layers. Previous studies on species diversity effect have generally overlooked the importance of the size structure and the size hierarchy of functional characteristics. These effects are, however, crucial and deserve to be explored in greater detail. [ABSTRACT FROM AUTHOR]

Damage due to wind-storms and droughts is increasing in many temperate forests, yet little is known about the long-term roles of these key climatic factors in forest dynamics and in the carbon budget. The objective of this study was to estimate individual and coupled effects of droughts and wind-storms on adult tree mortality across a 31-year period in 115 managed, mixed coniferous forest stands from the Western Alps and the Jura mountains. For each stand, yearly mortality was inferred from management records, yearly drought from interpolated fields of monthly temperature, precipitation and soil water holding capacity, and wind-storms from interpolated fields of daily maximum wind speed. We performed a thorough model selection based on a leave-one-out cross-validation of the time series. We compared different critical wind speeds ( CWSs) for damage, wind-storm, and stand variables and statistical models. We found that a model including stand characteristics, drought, and storm strength using a CWS of 25 ms−1 performed the best across most stands. Using this best model, we found that drought increased damage risk only in the most southerly forests, and its effect is generally maintained for up to 2 years. Storm strength increased damage risk in all forests in a relatively uniform way. In some stands, we found positive interaction between drought and storm strength most likely because drought weakens trees, and they became more prone to stem breakage under wind-loading. In other stands, we found negative interaction between drought and storm strength, where excessive rain likely leads to soil water saturation making trees more susceptible to overturning in a wind-storm. Our results stress that temporal data are essential to make valid inferences about ecological impacts of disturbance events, and that making inferences about disturbance agents separately can be of limited validity. Under projected future climatic conditions, the direction and strength of these ecological interactions could also change. [ABSTRACT FROM AUTHOR]

Trait-based approaches have been increasingly used to understand the role of environmental and biotic filters on species assembly. However, our understanding of the relationships between traits and community assembly processes remain limited. Indeed, various assembly processes may lead to similar functional patterns, and the effects of a given process may vary with the considered traits. Especially, competition can result in trait divergence or convergence depending on whether the trait is related to niche differences or to species' competitive abilities., In this study, we used a process-based forest gap-model to explore the effects of environmental and biotic assembly processes on the functional diversity of tree communities along a productivity gradient of 11 sites across central Europe. In a simulation experiment, we (i) disentangled the effects of environmental and biotic filtering on community structure, and (ii) tested whether competition resulted in trait divergence or convergence., Our results confirmed the expected decrease in species richness with decreasing site fertility. We detected environmental filtering for traits related to both species environmental requirements and species competitive ability, highlighting that environmental trait filtering can affect all aspects of tree life-history strategies., We observed convergence of traits related to growth and light capture resulting from competition for light, suggesting that tree species assembly is mainly driven by differences in competitive abilities. Additionally, the observed trait convergence was stronger in more productive sites than in less fertile ones, reflecting the impact of environmental conditions on competitive interactions., Synthesis. Our study shows that process-based forest gap-models can help to test whether functional traits composition reveal the signature of community assembly processes. This process-based approach challenges the classical view on the links between traits and mechanisms driving community assembly., A is available for this article. [ABSTRACT FROM AUTHOR]

Investigating how interactions among plants depend on environmental conditions is key to understand and predict plant communities' response to climate change. However, while many studies have shown how direct interactions change along climatic gradients, indirect interactions have received far less attention. In this study, we aim at contributing to a more complete understanding of how biotic interactions are modulated by climatic conditions. We investigated both direct and indirect effects of adult tree canopy and ground vegetation on seedling growth and survival in five tree species in the French Alps. To explore the effect of environmental conditions, the experiment was carried out at 10 sites along a climatic gradient closely related to temperature. While seedling growth was little affected by direct and indirect interactions, seedling survival showed significant patterns across multiple species. Ground vegetation had a strong direct competitive effect on seedling survival under warmer conditions. This effect decreased or shifted to facilitation at lower temperatures. While the confidence intervals were wider for the effect of adult canopy, it displayed the same pattern. The monitoring of micro-environmental conditions revealed that competition by ground vegetation in warmer sites could be related to reduced water availability; and weak facilitation by adult canopy in colder sites to protection against frost. For a cold-intolerant and shade-tolerant species ( Fagus sylvatica), adult canopy indirectly facilitated seedling survival by suppressing ground vegetation at high temperature sites. The other more cold tolerant species did not show this indirect effect ( Pinus uncinata, Larix decidua and Abies alba). Our results support the widely observed pattern of stronger direct competition in more productive climates. However, for shade tolerant species, the effect of direct competition may be buffered by tree canopies reducing the competition of ground vegetation, resulting in an opposite trend for indirect interactions across the climatic gradient. [ABSTRACT FROM AUTHOR]

Ecologists have limited understanding of how geographic variation in forest biomass arises from differences in growth and mortality at continental to global scales. Using forest inventories from across North America, we partitioned continental-scale variation in biomass growth and mortality rates of 49 tree species groups into (1) species-independent spatial effects and (2) inherent differences in demographic performance among species. Spatial factors that were separable from species composition explained 83% and 51% of the respective variation in growth and mortality. Moderate additional variation in mortality (26%) was attributable to differences in species composition. Age-dependent biomass models showed that variation in forest biomass can be explained primarily by spatial gradients in growth that were unrelated to species composition. Species-dependent patterns of mortality explained additional variation in biomass, with forests supporting less biomass when dominated by species that are highly susceptible to competition (e.g. Populus spp.) or to biotic disturbances (e.g. Abies balsamea). [ABSTRACT FROM AUTHOR]

Plant structural diversity is usually considered as beneficial for ecosystem functioning. For instance, numerous studies have reported positive species diversity-productivity relationships in plant communities. However, other aspects of structural diversity such as individual size inequality have been far less investigated. In forests, tree size inequality impacts directly tree growth and asymmetric competition, but consequences on forest productivity are still indeterminate. In addition, the effect of tree size inequality on productivity is likely to vary with species shade-tolerance, a key ecological characteristic controlling asymmetric competition and light resource acquisition. Using plot data from the French National Geographic Agency, we studied the response of stand productivity to size inequality for ten forest species differing in shade tolerance. We fitted a basal area stand production model that included abiotic factors, stand density, stand development stage and a tree size inequality index. Then, using a forest dynamics model we explored whether mechanisms of light interception and light use efficiency could explain the tree size inequality effect observed for three of the ten species studied. Size inequality negatively affected basal area increment for seven out of the ten species investigated. However, this effect was not related to the shade tolerance of these species. According to the model simulations, the negative tree size inequality effect could result both from reduced total stand light interception and reduced light use efficiency. Our results demonstrate that negative relationships between size inequality and productivity may be the rule in tree populations. The lack of effect of shade tolerance indicates compensatory mechanisms between effect on light availability and response to light availability. Such a pattern deserves further investigations for mixed forests where complementarity effects between species are involved. When studying the effect of structural diversity on ecosystem productivity, tree size inequality is a major facet that should be taken into account. [ABSTRACT FROM AUTHOR]

Understanding the long-term impacts of invasive mammalian browsers and granivores in mixed forests is difficult due to the many processes potentially affecting the demography of long-lived trees. We constructed individual-based spatially explicit simulation models of two mixed conifer-angiosperm forests, growing on soils of contrasting phosphorus (P) availability, to investigate how browsing by invasive red deer (Cervus elaphus scoticus) and granivory by invasive rodents (primarily house mouse Mus musculus) might alter forest dynamics. Models were parameterized with field data. Seedling growth and survival rates were estimated inside and outside deer exclosures. Seed predation rates were estimated at high and low rodent densities in mast and non-mast seeding years. For the alluvial terrace forest, which grew on P-rich soil, our model contained 15 tree species dominated by angiosperms; our model of the P-poor marine terrace forest contained seven species dominated by conifers. The two forest models were used to explore four 500-year scenarios: deer and rodents present, deer present and rodents absent, deer absent and rodents present, and deer and rodents absent. Our field studies revealed that the highest probabilities of seed predation by rodents occurred for two canopy species in mast years and in neighborhoods of high species-specific basal area, and that deer browsing had the greatest negative effects on the growth and survival rates of angiosperm seedlings. Our simulation models predicted that the presence of deer and rodents would reduce the abundances of canopy codominants, and hence total basal area, in the alluvial terrace forest. The presence of deer increased the dominance of conifers in both forests, but effects of deer and rodents were much stronger in the alluvial terrace forest. Our study revealed two emergent properties. First, rodent- and deer-induced reductions in seedling abundances did not always translate into reduced sapling and adult tree abundances. Second, when deer changed the abundance of a canopy dominant, other species were affected by altered interspecific competition. We conclude that the effects of invasive deer and rodents will be greatest in forests growing on P-rich soils. Exclusion of deer is predicted to have greater long-term effects on forest dynamics than exclusion of rodents. [ABSTRACT FROM AUTHOR]

Hutchinson defined species' realized niche as the set of environmental conditions in which populations can persist in the presence of competitors. In terms of demography, the realized niche corresponds to the environments where the intrinsic growth rate ( r) of populations is positive. Observed species occurrences should reflect the realized niche when additional processes like dispersal and local extinction lags do not have overwhelming effects. Despite the foundational nature of these ideas, quantitative assessments of the relationship between range-wide demographic performance and occurrence probability have not been made. This assessment is needed both to improve our conceptual understanding of species' niches and ranges and to develop reliable mechanistic models of species geographic distributions that incorporate demography and species interactions. The objective of this study is to analyse how demographic parameters (intrinsic growth rate r and carrying capacity K ) and population density ( N ) relate to occurrence probability ( Pocc ). We hypothesized that these relationships vary with species' competitive ability. Demographic parameters, density, and occurrence probability were estimated for 108 tree species from four temperate forest inventory surveys (Québec, western USA, France and Switzerland). We used published information of shade tolerance as indicators of light competition strategy, assuming that high tolerance denotes high competitive capacity in stable forest environments. Interestingly, relationships between demographic parameters and occurrence probability did not vary substantially across degrees of shade tolerance and regions. Although they were influenced by the uncertainty in the estimation of the demographic parameters, we found that r was generally negatively correlated with Pocc, while N, and for most regions K, was generally positively correlated with Pocc. Thus, in temperate forest trees the regions of highest occurrence probability are those with high densities but slow intrinsic population growth rates. The uncertain relationships between demography and occurrence probability suggests caution when linking species distribution and demographic models. [ABSTRACT FROM AUTHOR]

Global warming is predicted to dramatically alter communities' composition through differential colonization abilities, such as between sessile plants and their mobile herbivores. Novel interactions between previously non-overlapping species may, however, also be mediated by altered plants' responses to herbivore attack., Syndromes of plant defences and tolerance are driven by inherited functional traits, biotic and abiotic conditions, and the geographical and historical contingencies affecting the community. Therefore, understanding climate change-driven herbivore responses and evolution towards a particular plant defence syndrome is key to forecasting species interactions in the near future., In this paper, we first document variations in herbivory, and plant defences along altitudinal gradients that act as 'natural experiments'. We then use an empirical model to predict how specialist herbivore abundance may shift with respect to elevation in the near future., Our field surveys and field experiment showed a decrease in herbivory with elevation. However, contrary to expectations, our meta-regression analyses showed that plant defences, particularly leaf toughness and flavonoid compounds, tend to be higher at high elevations, while secondary metabolites showed no clear trend with elevation., Based on those results, we discuss how plant communities and species-specific plant defence syndromes will change in response to the climate-driven herbivore colonization of higher altitudes. Particularly, plant from high elevation, due to high protection against abiotic stress may be already ecologically fitted to resist the sudden increase in herbivory pressure that they will likely experience during global change. [ABSTRACT FROM AUTHOR]

Climate change is expected to increase the magnitude and the frequency of extreme climatic events such as droughts. Better understanding how plant communities will respond to these droughts is a major challenge. We expect the response to be a shift in functional trait values resulting from both species turnover and intraspecific trait variability, but little research has addressed the relative contribution of both components., We analysed the short-term functional response of subalpine grassland communities to a simulated drought by focusing on four leaf traits ( LDMC: leaf dry matter content, SLA: specific leaf area, LNC: leaf nitrogen concentration and LCC: leaf carbon concentration). After evaluating species turnover and intraspecific variability separately, we determined their relative contribution in the community functional response to drought, reflected by changes in community-weighted mean traits., We found significant species turnover and intraspecific variability, as well as significant changes in community-weighted mean for most of the traits. The relative contribution of intraspecific variability to the changes in community mean traits was more important (42-99%) than the relative contribution of species turnover (1-58%). Intraspecific variability either amplified (for LDMC, SLA and LCC) or dampened (for LNC) the community functional response mediated by species turnover. We demonstrated that the small contribution of species turnover to the changes in community mean LDMC and LCC was explained by a lack of covariation between species turnover and interspecific trait differences., Synthesis. These results highlight the need for a better consideration of intraspecific variability to understand and predict the effect of climate change on plant communities. While both species turnover and intraspecific variability can be expected following an extreme drought, we report new evidence that intraspecific variability can be a more important driver of the short-term functional response of plant communities. [ABSTRACT FROM AUTHOR]

The importance of competition has been defined as the impact or role of competition relative to the total impact of the environment, and the intensity of competition is its absolute impact. Understanding the distinction has been proposed as key in reconciling long-running ecological debates., An index of competition importance, Cimp, has been used in a number of recent studies. Rees, Childs & Freckleton (2012) present a strong attack on the competition index Cimp (and the associated interaction index Iimp) and question the underlying rationale for the concept of competition importance. We assess their critique and challenge it in a number of areas., Rees et al. conflate criticism of the index Cimp with criticism of the concept of competition importance. Their approach to assessing the properties of Cimp (and Iimp), including the use of target plant success in the absence of neighbours ( PNC) as a measure of environmental severity, is biased towards demonstrating a simple linear relationship between severity and Cimp, and supporting the argument that there is no need for separate measurements of importance., We consider the proposal by Rees et al. for the use of variance partitioning to assess importance. Although providing a measure of the relative role of competition, it is unable to assess the shape of the importance-severity relationship, something central to testing important ecological theories such as those of Grime (1979) or Bertness & Callaway (1994). We discuss alternative approaches which might address this question., Synthesis. Responding to Rees et al. has been beneficial in clarifying points of difference between our approaches, and the need to visualize the shape of the importance-severity relationship. From this response we draw three broad conclusions. We need: (i) metrics of environmental severity that are independent of the success of target species; (ii) analytical approaches that avoid the statistical problems associated with ratios whilst enabling us to assess the shape of the severity-importance relationship; (iii) new data to assess the generality of proposed relationships. Studies incorporating these elements will take forward our understanding of the role of competition in plant communities. [ABSTRACT FROM AUTHOR]

Predicting climate-driven changes in plant distribution is crucial for biodiversity conservation and management under recent climate change. Climate warming is expected to induce movement of species upslope and towards higher latitudes. However, the mechanisms and physiological processes behind the altitudinal and latitudinal distribution range of a tree species are complex and depend on each tree species features and vary over ontogenetic stages. We investigated the altitudinal distribution differences between juvenile and adult individuals of seven major European tree species along elevational transects covering a wide latitudinal range from southern Spain (37°N) to northern Sweden (67°N). By comparing juvenile and adult distributions (shifts on the optimum position and the range limits) we assessed the response of species to present climate conditions in relation to previous conditions that prevailed when adults were established. Mean temperature increased by 0.86 °C on average at our sites during the last decade compared with previous 30-year period. Only one of the species studied, Abies alba, matched the expected predictions under the observed warming, with a maximum abundance of juveniles at higher altitudes than adults. Three species, Fagus sylvatica, Picea abies and Pinus sylvestris, showed an opposite pattern while for other three species, such as Quercus ilex, Acer pseudoplatanus and Q. petraea, we were no able to detect changes in distribution. These findings are in contrast with theoretical predictions and show that tree responses to climate change are complex and are obscured not only by other environmental factors but also by internal processes related to ontogeny and demography. [ABSTRACT FROM AUTHOR]

Context: There is strong interest in sustainable forest management systems that preserve characteristics of forests close to naturalness. Assessing the effectiveness of these systems is difficult because defining 'natural' baselines from which impacts are estimated is challenging and because the influence of harvesting can have complex interactions with major natural disturbances. Aims: We used SORTIE/NZ, an individual tree-based forest dynamics model, to understand how harvesting and earthquake disturbance affect the dynamics of a New Zealand podocarp-angiosperm forest. Methods: Having parameterized SORTIE/NZ with extensive field data, we ran simulations for three natural dynamics scenarios (no disturbance and two earthquake scenarios) and then added podocarp harvesting scenario to each of these. Results: Simulations suggest that this forest is experiencing transient dynamics, with a natural rise in the dominance of one species of slow-growing podocarp with and without earthquake. Harvesting podocarps strongly affected its increase in basal area. Conclusion: Our results indicate that transient dynamics may occur in mixed podocarp forests and major disturbances may have complex interactions with management. Evaluating management impacts without accounting for these complex dynamics may be misleading. Models make predictions about transient trajectories that may help to evaluate these impacts. [ABSTRACT FROM AUTHOR]

Background: Despite empirical support for an increase in ecosystem productivity with species diversity in synthetic systems, there is ample evidence that this relationship is dependent on environmental characteristics, especially in structurally more complex natural systems. Empirical support for this relationship in forests is urgently needed, as these ecosystems play an important role in carbon sequestration. Methodology/Principal Findings: We tested whether tree wood production is positively related to tree species richness while controlling for climatic factors, by analyzing 55265 forest inventory plots in 11 forest types across five European countries. On average, wood production was 24% higher in mixed than in monospecific forests. Taken alone, wood production was enhanced with increasing tree species richness in almost all forest types. In some forests, wood production was also greater with increasing numbers of tree types. Structural Equation Modeling indicated that the increase in wood production with tree species richness was largely mediated by a positive association between stand basal area and tree species richness. Mean annual temperature and mean annual precipitation affected wood production and species richness directly. However, the direction and magnitude of the influence of climatic variables on wood production and species richness was not consistent, and vary dependent on forest type. Conclusions: Our analysis is the first to find a local scale positive relationship between tree species richness and tree wood production occurring across a continent. Our results strongly support incorporating the role of biodiversity in management and policy plans for forest carbon sequestration. [ABSTRACT FROM AUTHOR]

The relative importance of competition vs. environmental filtering in the assembly of communities is commonly inferred from their functional and phylogenetic structure, on the grounds that similar species compete most strongly for resources and are therefore less likely to coexist locally. This approach ignores the possibility that competitive effects can be determined by relative positions of species on a hierarchy of competitive ability. Using growth data, we estimated 275 interaction coefficients between tree species in the French mountains. We show that interaction strengths are mainly driven by trait hierarchy and not by functional or phylogenetic similarity. On the basis of this result, we thus propose that functional and phylogenetic convergence in local tree community might be due to competition-sorting species with different competitive abilities and not only environmental filtering as commonly assumed. We then show a functional and phylogenetic convergence of forest structure with increasing plot age, which supports this view. [ABSTRACT FROM AUTHOR]

Intra-specific variability often produces an overlap between species distributions of individual performances which can influence competition relations and community dynamics. We analysed a two-species competition-colonisation model of vegetation with intra-specific variability in juvenile growth. On each patch colonised by both species, the winner was the juvenile with higher individual growth. Intra-specific variability disproportionately favoured the more fecund species because the tail of its distribution represented more individuals. In some cases, this process could even lead to a reversal of competition hierarchy and exclusion of the species with higher mean juvenile performance. In the space of species 2 mean growth and fecundity traits, the combinations of traits allowing coexistence with species 1 appeared close to an ideal trade-off curve. Along this curve, species 2 and species 1 coexisted at similar abundance. The balance of relative abundances diminished with the distance of species 2 from this curve. For a given level of relative species performances, coexistence stability increased continuously as species differentiation increased. In contrast to classical models that exhibit abrupt changes of equilibrium community properties when species traits vary, our model displayed continuous changes of these properties in relation to the balance of life traits within and among species. Intra-specific variability allows flexible patterns of community dynamics and could explain discrepancies between observations and classical theories. [ABSTRACT FROM AUTHOR]

Plant interactions play a central role in regulating plant communities and this role can be altered by abiotic stress. With increasing stress, ecological theory predicts that the role of competition decreases whilst that of facilitation increases. Such predictions have been tested with short-term plant removal experiments using two distinct indices evaluating the role of plant interactions: the intensity (absolute impact) and the importance (impact relative to that of other abiotic constraints) of plant interactions. Using data on individual tree radial growth from more than 17 000 forest plots covering the habitat conditions of 16 species in the Alps and the Jura mountains of France, we show that non-manipulative estimates of plant interactions provide an alternative to this experimental approach. We developed a Bayesian neighbourhood growth competition model to test theoretical predictions about plant-plant interactions with a much larger spatio-temporal scope and set of study species than classically used in experimental studies of plant-plant interactions. Our analyses revealed that competition - measured as neighbours effects on adult tree growth - varies in importance but not in intensity along two major bioclimatic gradients (degree-day sum and water availability). Observed patterns of competition importance differed between shade-tolerant and shade-intolerant tree species. First, the mean importance of competition was found to be much higher for shade-intolerant species. Second, for shade-intolerant species the importance of competition remained high even at low crowding indices (i.e. at a low competitor density), whereas for shade-tolerant species competition only became important at high crowding indices. Synthesis. Our non-manipulative approach to the study of plant-plant interactions allows analysing interactions among many species over large climatic gradients. Our results clearly demonstrate that a quantitative estimation of density dependence effects is key to understanding how plant-plant interactions vary along abiotic gradients. Growth predictions derived from our model can easily be integrated with other results on tree regeneration and mortality in individual-based models to investigate how plant-plant interactions drive tree population and community dynamics under varying climatic conditions. [ABSTRACT FROM AUTHOR]

Tree species differences in crown size and shape are often highlighted as key characteristics determining light interception strategies and successional dynamics. The phenotypic plasticity of species in response to light and space availability suggests that intraspecific variability can have potential consequences on light interception and community dynamics. Species crown size varies depending on site characteristics and other factors at the individual level which differ from competition for light and space. These factors, such as individual genetic characteristics, past disturbances or environmental micro-site effects, combine with competition-related phenotypic plasticity to determine the individual variability in crown size. Site and individual variability are typically ignored when considering crown size and light interception by trees, and residual variability is relegated to a residual error term, which is then ignored when studying ecological processes. In the present study, we structured and quantified variability at the species, site, and individual levels for three frequently used tree allometric relations using fixed and random effects in a hierarchical Bayesian framework. We focused on two species: Abies alba (silver fir) and Picea abies (Norway spruce) in nine forest stands of the western Alps. We demonstrated that species had different allometric relations from site to site and that individual variability accounted for a large part of the variation in allometric relations. Using a spatially explicit radiation transmission model on real stands, we showed that individual variability in tree allometry had a substantial impact on light resource allocation in the forest. Individual variability in tree allometry modulates species’ light-intercepting ability. It generates heterogeneous light conditions under the canopy, with high light micro-habitats that may promote the regeneration of light-demanding species and slow down successional dynamics. [ABSTRACT FROM AUTHOR]

1. Due to species-specificity of the outcomes of biotic interactions, it is difficult to generalize from observed biotic interactions at the individual plant level to the effect of those interactions at the community level. To evaluate the importance of biotic interactions in shaping plant communities, it is necessary to understand how the outcomes of the complex interactions observed at the individual level can influence community structure. 2. Here, we propose a trait-based framework that identifies and organises mechanisms affecting community structure (here described with relative abundances of plant functional traits – i.e. the distribution of trait values at the community level). We applied our approach to a single leaf trait, specific leaf area (SLA), to link individual responses to plant interactions with community structure (SLA distribution observed at the community level) and to test whether biotic interactions can predict the functional composition of subalpine grasslands. We evaluated the generality of our model through a cross-validation with a set of eight subalpine grasslands independent from the four fields used to build the model. 3. We found that competition and facilitation were able to explain the functional composition of subalpine grasslands, and the relevant fitness components (survival or growth) explaining this link changed depending on the limiting resources. When soil water availability was limiting, positive plant-plant interactions acting on survival were able to explain community structure. In contrast, when no water limitation was observed competition acting on individual growth was the main driver of community structure. 4. Our framework enables evaluation of the consequences of biotic interactions observed at individual level on community structure, thereby indicating when and where different types of plant-plant interactions are important. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Forest Research is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

1. A trade-off between growth in high-light and survival in low-light of species is often proposed as a key mechanism underpinning the dynamics of trees in forest communities. Yet, growth and survival are known to depend on plant size and few studies have analysed how this trade-off can vary between juvenile life stages and the potential consequences of the trade-off for the differences in regeneration rate between species in mixed forests. 2. We quantified growth and mortality for two different juvenile life stages – seedlings and saplings – of seven tree species common in temperate rain forests in New Zealand using data from field studies. We found strong evidence that the ranking of species for survival in shade and growth in full light was affected by size. There was a trade-off between seedling survival in low light and sapling height growth in high light, but no trade-offs were observed when considering other combinations of life stages (seedling growth vs. seedling survival, seedling growth vs. sapling survival, or sapling growth vs. sapling survival). 3. We ran simulations with an individual-based forest dynamics model – SORTIE/NZ – to explore how the trade-off drives the differences in tree species regeneration success in gaps vs. under closed forest conditions. These simulations indicate that because species’ ranks in shade tolerance varied with life stage, regeneration success was not predicted from knowledge of tree performance at a single life stage. For instance, high-light sapling growth was a strong determinant of regeneration success in forest gaps, but seedling growth was also influential. Under closed forest, regeneration success was primarily limited by low-light mortality at the seedling stage, but seedling growth and sapling survival were also influential. 4. Synthesis. Growth-survival trade-offs can be strongly affected by the size of the individual analysed, resulting in completely different rankings of the shade tolerance of species across different juvenile life stages. Performance of both seedlings and saplings influenced regeneration success, highlighting the need to consider growth-survival trade-offs and the shade-tolerance strategies of tree species over a large range of juvenile sizes. [ABSTRACT FROM AUTHOR]

1. A central concept in forest ecology is that differences in the growth rates and shade tolerances of tree species determine patterns of secondary succession. The most shade-tolerant tree species are the competitive dominants in late-successional forests, while species with fast growth rates persist through rapid establishment after disturbance. There is ample support for niche differentiation along the shade-tolerance axis, at least for temperate forests, but less thought has been given to the range of shade tolerances and growth rates encountered within a community and to how it might vary along environmental gradients. 2. We hypothesized that a wider range of growth rates and shade tolerances are found on nutrient-rich soils, because such soils not only support fast-growing species with high metabolic rates, but also species capable of tolerating the very deep shade cast by forest canopies growing where nutrients are plentiful. We test our hypothesis by quantifying light transmission through two neighbouring forests in southern New Zealand, one on phosphorus-rich alluvial soil and one on phosphorus-depleted marine-terrace soil, and comparing the growth rates of saplings on these contrasting sites. 3. Less light was transmitted to the forest floor on alluvial sites than on marine terraces (2.5% vs. 7.5% daylight, on average) and neighbourhood analyses within mapped stands indicated that large-leaved subcanopy species were responsible for intercepting that extra light. Sapling growth was strongly inhibited by shade in the understorey of the alluvial forests, but was less inhibited under the terrace forests. 4. Fast-growing subcanopy species were common on the alluvial sites and these species had characteristically soft leaves and high foliar-nutrient concentrations. Slow-growing shade-tolerant species were also abundant on these sites. Therefore, the interspecific variance in growth rates was greater on nutrient-rich sites, supporting our hypothesis of a greater range of shade tolerance niches on better soils. Of the five species found on both forest sites, all five had greater high-light growth rate on the alluvial sites. 5. Synthesis: A wider range of growth rates was observed in the nutrient-rich forests. This wider range may translate into a greater number of shade tolerance niches and thereby provides an explanation for the greater numbers of species commonly found on nutrient-rich soils when compared with neighbouring nutrient-poor sites. [ABSTRACT FROM AUTHOR]

1. Once neglected, the role of facilitative interactions in plant communities has received considerable attention in the last two decades, and is now widely recognized. It is timely to consider the progress made by research in this field. 2. We review the development of plant facilitation research, focusing on the history of the field, the relationship between plant–plant interactions and environmental severity gradients, and attempts to integrate facilitation into mainstream ecological theory. We then consider future directions for facilitation research. 3. With respect to our fundamental understanding of plant facilitation, clarification of the relationship between interactions and environmental gradients is central for further progress, and necessitates the design and implementation of experiments that move beyond the clear limitations of previous studies. 4. There is substantial scope for exploring indirect facilitative effects in plant communities, including their impacts on diversity and evolution, and future studies should connect the degree of non-transitivity in plant competitive networks to community diversity and facilitative promotion of species coexistence, and explore how the role of indirect facilitation varies with environmental severity. 5. Certain ecological modelling approaches (e.g. individual-based modelling), although thus far largely neglected, provide highly useful tools for exploring these fundamental processes. 6. Evolutionary responses might result from facilitative interactions, and consideration of facilitation might lead to re-assessment of the evolution of plant growth forms. 7. Improved understanding of facilitation processes has direct relevance for the development of tools for ecosystem restoration, and for improving our understanding of the response of plant species and communities to environmental change drivers. 8. Attempts to apply our developing ecological knowledge would benefit from explicit recognition of the potential role of facilitative plant–plant interactions in the design and interpretation of studies from the fields of restoration and global change ecology. 9. Synthesis: Plant facilitation research provides new insights into classic ecological theory and pressing environmental issues. Awareness and understanding of facilitation should be part of the basic ecological knowledge of all plant ecologists. [ABSTRACT FROM AUTHOR]

Native tree populations have been fragmented by anthropogenic disturbance worldwide, leaving them at risk from extinction. The possibility of sizable recovery of fragmented populations is a function of their dispersal, the abiotic conditions, and the biotic interactions. The relative importance of these three drivers for the recruitment rate of a fragmented population of the late-successional Fagus sylvatica L. was analysed at the landscape scale in Causse du Larzac, southern margins of the Massif Central, in the South of France. We used regression models on observational data to analyse the response of Fagus recruitment rate to the distance to the nearest mature population, to climatic and geological variables, and to variables describing biotic interactions (pine vs. grassland, light, shrub cover). Distance to the nearest F. sylvatica adult population was the most important explanatory variable. Recruitment rate was also influenced by facilitative biotic interactions with shrubs, and by the climatic conditions of the plot. Recruitment occurred at a greater distance from the nearest mature population of Fagus in pine forests than in grassland. Dispersal was the major limitation to recruitment of F. sylvatica in this landscape. The recruitment rate was then modulated by the climate and positive biotic interactions. The activity of the European jay could be of great importance for such fragmented populations, because it can lead to long-distance dispersal events and may result in a preferential dispersal towards pine forests. [ABSTRACT FROM AUTHOR]

1. A prominent idea in the literature on plant–herbivore interactions is that fast-growing species have low resistance but high resilience to herbivory. In other words, fast-growing species are selectively eaten by herbivores but recover quickly following damage. Many studies have challenged the generality of this theory, but little attention has been paid to plant species that have evolved in the absence of major groups of herbivores. Here we analyse whether this resistance-resilience trade-off applies to New Zealand woody species, which evolved without exposure to mammalian herbivores until their introduction in 19th century. 2. We simulated deer browse by clipping saplings of 12 tree species to varying extents (0, 20, 40, 80 and 100% of leaf-bearing branches removed), and quantified the shoot growth, diameter growth and survival of these saplings. The time taken to regrow the removed branches was generally slow, but varied among species. For example, species took between 0.5 and 3 years to recover from removal of 60% of branches. It was the inherently fast-growing species that recovered most quickly. Some species had stimulated shoot growth at moderate levels of clipping (40–60%) but this effect had relatively little effect on recovery time compared with differences in potential growth rates of species. 3. Diameter growth rate fell linearly with increased clipping intensity for all 12 species, and there was no indication of recovery 2 years after the treatment. We speculate that saplings invested in rebuilding their canopies following clipping, and that few resources were left over for diameter growth. 4. Few saplings died as a result of clipping, except when 100% of leaf-bearing shoots were removed, in which case five species died in substantial numbers (> 15%), including all three conifers in the study. 5. Previous work has shown that the most palatable species (i.e. those with low resistance) have leaves with low fibre content. We find that these species are relatively fast growing and recover most rapidly from simulated browsing (i.e. are highly resilient). This provides some support for a resistance-resilience trade-off related to potential growth rates. 6. Deer invasion in New Zealand was associated with the loss of short soft-leaved tree species from the browse layer. Our study suggests that the most palatable species have the potential to grow fast and may be in a relatively strong position to recover if deer are eradicated. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Forest Research is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Canadian Journal of Forest Research is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

1. Molecular techniques have greatly added to the number of known sympatric cryptic species in insects. Ecological differences between these newly distinguished species are little explored, but niches often appear to overlap strongly. These cases are good models for exploring new ideas about species coexistence and community structure. 2. Acanthoscelides obtectus and A. obvelatus are two sister species of bean bruchids, which have been confused until the last decade. One important ecological difference between them has emerged, however: A. obtectus is multivoltine and now distributed worldwide, whereas A. obvelatus is univoltine and restricted to Mesoamerica. Where their ranges overlap, the two species share the same host plants and larvae can sometimes complete development in the same seed. 3. The analysis of 27 622 Mexican individuals of the two species in 2001-2002 and 2002-2003 indicates that their niches overlap, but are differentiated with respect to altitude and the kind of beans (wild vs. domesticated). The principal patterns in their relative abundance in different habitats, and at different seasons, were constant from one year to the next. 4. As sympatry of these species seems to be of recent origin, the observed niche differentiation may not have evolved in response to competition, but could instead be the consequence of physiological differences, evolved independently in each species in allopatry, that pre-adapted them for different altitudes and kinds of resources. 5. The combination of biological and historical factors thus appears to allow these two sibling species to coexist in sympatry, despite their broadly overlapping ecological niches. [ABSTRACT FROM AUTHOR]

Questions: In the absence of herbivores, what is the importance of shrub facilitation for the colonization of grasslands by Fagus sylvatica and Quercus pubescens? Is there an indirect facilitative effect of shrubs on tree seedlings by limiting herb competition? Location: Causse du Larzac, southern Massif Central, France. Methods: We conducted field experiments on the facilitative role of shrubs in seedling emergence and survival, in relation to potential negative effects of shading and the presence of herbs. The effects of shade and herbs on allocation and root morphology were analysed in a pot experiment. Results: According to these experiments, the establishment of both tree species was facilitated by shrubs, but the two species differed in the processes underlying this facilitation. Shade directly facilitates the emergence rate of both species. Shade also indirectly facilitates Fagus survival by limiting herb competition. No indirect facilitation of Quercus survival was detected. These differences reflect variation in the tolerance of herb competition by seedlings of the two species. The tolerance of herb competition by Quercus seedlings allows regeneration over a wide area under each shrub and some regeneration events in grasslands at low grazing intensity. In contrast, for Fagus, only a narrow area under each shrub is suitable; regeneration is zero in grassland. The high tolerance of herb competition by Quercus seedlings may result from the avoidance of root competition. Conclusions: In grasslands with severe drought stress, and almost obligatory shrub facilitation for tree seedling regeneration, the tolerance of herb competition may alter the precise role of facilitation in the colonization process. [ABSTRACT FROM AUTHOR]

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