Range maps of thousands of species, compiled and made freely available by the International Union for Conservation of Nature, are being increasingly applied to support spatial conservation planning. ...However, their coarse nature makes them prone to commission and omission errors, and they lack information on the variations in abundance within species’ distributions, calling into question their value to inform decisions at the fine scales at which conservation often takes place. Here, we tested if species ranges can reliably be used to estimate the responsibility of sites for the global conservation of species. We defined ‘specific responsibility’ as the fraction of a species’ population within a given site, considering it useful for prioritising species within sites; and defined ‘overall responsibility’ as the sum of specific responsibility across species within a site, assuming it informative of priorities among sites. Taking advantage of an exceptionally detailed dataset on the distribution and abundance of bird species at a near‐continental scale – a level of information rarely available to local decision‐makers – we created a benchmark against which we tested estimates of responsibility derived from range maps. We investigated approaches for improving these estimates by complementing range maps with plausibly available local data. We found that despite their coarse nature, range maps provided good estimates of sites’ overall responsibility, but relatively poor estimates of specific responsibility. Estimates were improved by combining range maps with local species lists or local abundance data, easily available through local surveys on the sites of interest, or simulated expert knowledge. Our results suggest that combining range maps with local data is a promising route for improving the effectiveness of local conservation decisions at contributing to reducing global biodiversity losses. This is all the more urgent in hyper‐diverse poorly‐known regions where conservation‐relevant decisions must proceed despite a paucity of biodiversity data.
Secondary forests are a prominent component of tropical landscapes, and they constitute a major atmospheric carbon sink. Rates of carbon accumulation are usually inferred from chronosequence studies, ...but direct estimates of carbon accumulation based on long-term monitoring of stands are rarely reported. Recent compilations on secondary forest carbon accumulation in the Neotropics are heavily biased geographically as they do not include estimates from the Guiana Shield. We analysed the temporal trajectory of aboveground carbon accumulation and floristic composition at one 25-ha secondary forest site in French Guiana. The site was clear-cut in 1976, abandoned thereafter, and one large plot (6.25 ha) has been monitored continuously since. We used Bayesian modeling to assimilate inventory data and simulate the long-term carbon accumulation trajectory. Canopy change was monitored using two aerial lidar surveys conducted in 2009 and 2017. We compared the dynamics of this site with that of a surrounding old-growth forest. Finally, we compared our results with that from secondary forests in Costa Rica, which is one of the rare long-term monitoring programs reaching a duration comparable to our study. Twenty years after abandonment, aboveground carbon stock was 64.2 (95% credibility interval 46.4, 89.0) Mg C/ha, and this stock increased to 101.3 (78.7, 128.5) Mg C/ha 20 yr later. The time to accumulate one-half of the mean aboveground carbon stored in the nearby old-growth forest (185.6 155.9, 200.2 Mg C/ha) was estimated at 35.0 20.9, 55.9 yr. During the first 40 yr, the contribution of the long-lived pioneer species Xylopia nitida, Goupia glabra, and Laetia procera to the aboveground carbon stock increased continuously. Secondary forest mean-canopy height measured by lidar increased by 1.14 m in 8 yr, a canopy-height increase consistent with an aboveground carbon accumulation of 7.1 Mg C/ha (or 0.89 Mg C·ha-1·yr-1) during this period. Long-term AGC accumulation rate in Costa Rica was almost twice as fast as at our site in French Guiana. This may reflect higher fertility of Central American forest communities or a better adaptation of the forest tree community to intense and frequent disturbances. This finding may have important consequences for scaling-up carbon uptake estimates to continental scales.
Summary
Water stress can cause declines in plant function that persist after rehydration. Recent work has defined ‘resilience’ traits characterizing leaf resistance to persistent damage from drought, ...but whether these traits predict resilience in whole‐plant function is unknown. It is also unknown whether the coordination between resilience and ‘resistance’ – the ability to maintain function during drought – observed globally occurs within ecosystems.
For eight rainforest species, we dehydrated and subsequently rehydrated leaves, and measured water stress thresholds for declines in rehydration capacity and maximum quantum yield of photosystem II (Fv/Fm). We tested correlations with embolism resistance and dry season water potentials (ΨMD), and calculated safety margins for damage (ΨMD – thresholds) and tested correlations with drought resilience in sap flow and growth.
Ψ thresholds for persistent declines in Fv/Fm, indicating resilience, were positively correlated with ΨMD and thresholds for leaf vein embolism. Safety margins for persistent declines in Fv/Fm, but not rehydration capacity, were positively correlated with drought resilience in sap flow.
Correlations between resistance and resilience suggest that species' differences in performance during drought are perpetuated after drought, potentially accelerating shifts in forest composition. Resilience to photochemical damage emerged as a promising functional trait to characterize whole‐plant drought resilience.
Community composition is a primary determinant of how biodiversity change influences ecosystem functioning and, therefore, the relationship between biodiversity and ecosystem functioning (BEF). We ...examine the consequences of community composition across six structurally realistic plant community models. We find that a positive correlation between species’ functioning in monoculture versus their dominance in mixture with regard to a specific function (the “function‐dominance correlation”) generates a positive relationship between realised diversity and ecosystem functioning across species richness treatments. However, because realised diversity declines when few species dominate, a positive function‐dominance correlation generates a negative relationship between realised diversity and ecosystem functioning within species richness treatments. Removing seed inflow strengthens the link between the function–dominance correlation and BEF relationships across species richness treatments but weakens it within them. These results suggest that changes in species’ identities in a local species pool may more strongly affect ecosystem functioning than changes in species richness.
We examine the consequences of community composition on the structure of biodiversity and ecosystem functioning (BEF) relationships across six structurally‐realistic plant community models. We find that the correlation between species' functioning in monoculture vs. their dominance in mixture with regards to a specific function (A, B; the "function‐dominance correlation") generates contrasting BEF patterns across and within species richness treatments (C). These results, supported by empirical BEF results, suggest that changes in species' identities in a local species pool may more strongly affect ecosystem functioning than changes in species richness.
Key message
We combined aerial LiDAR and ground sensors to map the spatial variation in micro-environmental variables of the tropical forest understory. We show that these metrics depend on forest ...type and proximity to canopy gaps. Our study has implications for the study of natural forest regeneration.
Context
Light impacts seedling dynamics and animals, either directly or through their effect on air temperature and relative humidity. However, the micro-environment of tropical forest understories is heterogeneous.
Aims
We explored whether aerial laser scanning (LiDAR) can describe short-scale micro-environmental variables. We also studied the determinants of their spatial and intra-annual variation.
Methods
We used a small-footprint LiDAR coverage combined with data obtained from 47 environmental sensors monitoring continuously understory light, moisture and temperature during 1 year over the area. We developed and tested two models relating micro-environmental conditions to LiDAR metrics.
Results
We found that a volume-based model predicts empirical light fluxes better than a model based on the proportion of the LiDAR signal reaching the ground. Understory field sensors measured an average daily light flux between 2.9 and 4.7% of full sunlight. Relative seasonal variation was comparable in the understory and in clearings. In canopy gaps, light flux was 4.3 times higher, maximal temperature 15% higher and minimal relative humidity 25% lower than in the forest understory. We found consistent micro-environmental differences among forest types.
Conclusions
LiDAR coverage improves the fine-scale description of micro-environmental variables of tropical forest understories. This opens avenues for modelling the distribution and dynamics of animal and plant populations.
Intraspecific variability (IV) has been proposed to explain species coexistence in diverse communities. Assuming, sometimes implicitly, that conspecific individuals can perform differently in the ...same environment and that IV increases niche overlap, previous studies have found contrasting results regarding the effect of IV on species coexistence. We aim at showing that the large IV observed in data does not mean that conspecific individuals are necessarily different in their response to the environment and that the role of high‐dimensional environmental variation in determining IV has largely remained unexplored in forest plant communities. We first used a simulation experiment where an individual attribute is derived from a high‐dimensional model, representing “perfect knowledge” of individual response to the environment, to illustrate how large observed IV can result from “imperfect knowledge” of the environment. Second, using growth data from clonal Eucalyptus plantations in Brazil, we estimated a major contribution of the environment in determining individual growth. Third, using tree growth data from long‐term tropical forest inventories in French Guiana, Panama and India, we showed that tree growth in tropical forests is structured spatially and that despite a large observed IV at the population level, conspecific individuals perform more similarly locally than compared with heterospecific individuals. As the number of environmental dimensions that are well quantified at fine scale is generally lower than the actual number of dimensions influencing individual attributes, a great part of observed IV might be represented as random variation across individuals when in fact it is environmentally driven. This mis‐representation has important consequences for inference about community dynamics. We emphasize that observed IV does not necessarily impact species coexistence per se but can reveal species response to high‐dimensional environment, which is consistent with niche theory and the observation of the many differences between species in nature.
Intraspecific variability is often assumed to result from intrinsic differences between conspecific individuals, being represented as random variation. Based on multiple insights from theory, experimental, and empirical data, we emphasize this is often not the case, with radically different consequences for community dynamics.
Climate extremes and biotic interactions at the neighbourhood scale affect tropical forest dynamics with long‐term consequences for biodiversity, global carbon cycling and climate change mitigation. ...However, forest disturbance may change crowding intensity, and thus the relative contribution of climate extremes and neighbourhood interactions on tree growth, thereby influencing tropical forest resistance and resilience to climate change. Here, we aim to evaluate the separate and interactive effects of climate and neighbours on tree growth in old‐growth and disturbed tropical forests.
We used 30 years of growth measurements for over 300 tropical tree species from 15 forest plots in French Guiana to investigate the separate and interactive effects of climate anomalies (in solar radiation, maximum temperature, vapour pressure deficit and climatic water deficit) and neighbourhood crowding on individual tree growth. Contrasting old‐growth and selectively logged forests, we also examined how disturbance history affects tree growth sensitivity to climate and neighbours. Finally, for the most abundant 100 species, we evaluated the role of 12 functional traits pertaining to water relations, light and carbon use in mediating tree growth sensitivity to climate anomalies, neighbourhood crowding and their interactions.
Climate anomalies tied to heat and drought stress and neighbourhood crowding independently reduced tree growth, and showed positive interactive effects which attenuated their separate effects on tree growth. Their separate and interactive effects were stronger in disturbed than undisturbed forests. Fast‐growing species (i.e. higher intrinsic growth rates) were more abundant in disturbed forests and more sensitive to climate anomalies and neighbourhood crowding. Traits related to water relations, light and carbon use captured species sensitivities to different climate anomalies and neighbourhood crowding levels but were weak predictors of their interactions.
Synthesis: Our results demonstrate that climate anomalies and neighbourhood crowding can interact to shape tropical tree growth, suggesting that considering the biotic context may improve predictions of tropical forest dynamics facing altered climate regimes. Furthermore, species traits can capture tree growth sensitivity to the separate effects of climate and neighbours, suggesting that better representing leading functional dimensions in tropical tree strategies offers a promising way towards a better understanding of the underlying ecological mechanisms that govern tropical forest dynamics.
Résumé
Les extrêmes climatiques ainsi que les interactions biotiques à l'échelle du voisinage, affectent la dynamique des forêts tropicales, avec des conséquences à long terme pour la biodiversité, le cycle global du carbone et l'atténuation du changement climatique. Cependant, les perturbations forestières peuvent faire varier localement les voisinages, et ainsi modifier la contribution relative des extrêmes climatiques et des interactions de voisinage sur la croissance des arbres, ce qui peut impacter la résistance et la résilience des forêts tropicales au changement climatique. Nos travaux visent à évaluer les effets individuels et interactifs du climat et des voisins sur la croissance des arbres dans les forêts tropicales non‐pertubées et perturbées.
Nous avons utilisé 30 ans de mesures de croissance pour plus de 300 espèces d'arbres tropicaux provenant de 15 parcelles forestières en Guyane française pour étudier les effets individuels et interactifs des anomalies climatiques (en termes de rayonnement solaire, de température maximale, de déficit de pression de vapeur, et de déficit hydrique climatique) et des interactions de voisinage sur la croissance individuelle des arbres. En comparant les forêts exploitées sélectivement aux forêtsnon‐pertubées, nous avons également examiné comment l'historique des perturbations peut influencer la sensibilité de la croissance des arbres au climat et aux voisins. Enfin, pour les 100 espèces les plus abondantes, nous avons évalué le rôle de 12 traits fonctionnels reflétant les relations hydriques, l'utilisation de la lumière et du carbone sur la réponse de la croissance des arbres aux anomalies climatiques, aux interactions de voisinage et à leurs interactions.
Les anomalies climatiques liées aux stress thermique et hydrique, ainsi que les interactions de voisinage, réduisent la croissance des arbres. De plus, elles peuvent interagir positivement, ce qui atténue leurs effets individuels sur la croissance des arbres. Leurs effets individuels et interactifs sont plus forts dans les forêts perturbées que dans les forêts non‐perturbées. Les espèces à croissance rapide (c'est‐à‐dire à taux de croissance intrinsèque plus élevé) sont plus abondantes dans les forêts perturbées, et aussi plus sensibles aux anomalies climatiques et aux interactions de voisinage. Les traits liées aux relations hydriques, à la lumière et à l'utilisation du carbone captent la sensibilité des espèces aux différentes anomalies climatiques et aux différents niveaux d'interactions de voisinage, mais ne prédisent pas leurs interactions.
Synthèse: Nos résultats montrent que les anomalies climatiques et les interactions de voisinage peuvent interagir pour façonner la croissance des arbres tropicaux, ce qui suggère que prendre en compte le contexte biotique peut améliorer les prévisions de la dynamique des forêts tropicales face aux changements climatiques. En outre, les traits des espèces peuvent capter la sensibilité de la croissance des arbres aux effets individuels du climat et des voisins, ce qui suggère que mieux représenter les principales dimensions des stratégies fonctionnelles des arbres tropicaux ouvre sur une meilleure compréhension des mécanismes écologiques qui régissent la dynamique des forêts tropicales.
A 30‐year monitoring of tropical wet forests reveals that drought‐related climate anomalies can interact with neighbourhood crowding to shape tree growth and that tree growth in disturbed forests is more sensitive to climate stress and neighbourhood crowding than in old‐growth forests. Traits pertaining to light capture, carbon use and water relations captured variation in species sensitivities to climate and neighbours.
Water availability is a key determinant of forest ecosystem function and tree species distributions. While droughts are increasing in frequency in many ecosystems, including in the tropics, plant ...responses to water supply vary with species and drought intensity and are therefore difficult to model. Based on physiological first principles, we hypothesized that trees with a lower turgor loss point (πtlp), that is, a more negative leaf water potential at wilting, would maintain water transport for longer into a dry season.
We measured sapflux density of 22 mature trees of 10 species during a dry season in an Amazonian rainforest, quantified sapflux decline as soil water content decreased and tested its relationship to tree πtlp, size and leaf predawn and midday water potentials measured after the onset of the dry season.
The measured trees varied strongly in the response of water use to the seasonal drought, with sapflux at the end of the dry season ranging from 37 to 117% (on average 83 ± 5 %) of that at the beginning of the dry season. The decline of water transport as soil dried was correlated with tree πtlp (Spearman’s ρ ≥ 0.63), but not with tree size or predawn and midday water potentials. Thus, trees with more drought‐tolerant leaves better maintained water transport during the seasonal drought.
Our study provides an explicit correlation between a trait, measurable at the leaf level, and whole‐plant performance under drying conditions. Physiological traits such as πtlp can be used to assess and model higher scale processes in response to drying conditions.
A plain language summary is available for this article.
Plain Language Summary
Extreme wind blowdown events can significantly modify the structure and composition of forests, and the predicted shift in tropical cyclone regimes due to climate change could strongly impact forests ...across the tropics. In this study, we coupled an individual-based and spatially-explicit forest dynamics model (TROLL) with a mechanistic model estimating wind damage as a function of tree size, traits, and allometry (ForestGALES). We assimilated floristic trait data and climate data from a subtropical forest site in Taiwan to explore the effect of wind regimes on forest properties. We found that the average canopy height and biomass stocks decreased as wind disturbance strength increased, but biomass stocks showed a nonlinear response. Above a wind intensity threshold, both canopy height and biomass drastically decreased to near-zero, exhibiting a transition to a non-forest state. Wind intensity strongly regulated wind impact, but varying wind frequency did not cause discernible effects. The implementation of within-stand topographic heterogeneity led to weak effects on within-stand forest structure heterogeneity at the study site. In conclusion, the intensity of wind disturbances can potentially greatly impact forest structure by modifying mortality. Individual-based modeling provides a framework in which to investigate the impact of wind regimes on mortality, other factors influencing wind-induced tree mortality, as well as interaction between wind and other forms of forest disturbance and human land use legacy.
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