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Predicting plant community assembly is challenging in part because the influence of environmental conditions via plant functional strategies and the relevance of mechanisms of community assembly change across habitats and these changes remain poorly studied. To assess how environmental conditions drive species sorting in a tropical dry forest, we used the combined RLQ and Fourth‐Corner methods to analyse changes in tree species assemblages among sites with distinct atmospheric and soil drought risks. We asked how variation in potential radiation, soil water availability and evapotranspiration interact with functional traits to explain the cross‐site sorting of species lying along a continuum of drought coping strategies ranging from acquisitive to conservative resource‐use. Environment and traits were tightly related. Opposing common expectations on the success of strategies in resource limited environments, drought tolerant conservative species with dense tissues and tardily deciduous leaves were favoured on sites with higher resource (soil water) availability. Drought avoiding acquisitive species with water storing tissues and thin, light leaves with short retention time periods were favoured in sites with drier soils. A decoupling of stressing conditions caused by soil and atmospheric aridity combined with differences in species adaptations to each of these factors can explain the apparent discrepancies. Synthesis. Drought stress gradients entailed shifts in community functional composition. We show that atmospheric and soil drought risks can be decoupled and jointly determine species distribution in relation to their functional strategies. By considering atmospheric drought stress, a key yet often overlooked factor in studies of community assembly, we offer a novel explanation to a seemingly contrasting pattern in tropical dry forests where species with acquisitive, rather than conservative strategies, predominate in the most resource‐limited yet less water demanding environment. More generally, our results emphasize the need for detailed studies of the multiple habitat‐dependent relationships between traits and environment to advance our predictive understanding of species distributions and community assembly. Resumen Predecir el ensamblaje de las comunidades vegetales es una tarea compleja debido, en parte, a que la influencia de las condiciones ambientales, las cuales operan mediante las estrategias funcionales de las plantas, así como la relevancia de los mecanismos de ensamblaje comunitario, cambian a lo largo de distintos hábitats y estos aspectos todavía están insuficientemente abordados. Para evaluar cómo las condiciones ambientales determinan la segregación ecológica de especies en un bosque tropical estacionalmente seco, mediante el análisis de cambios en el ensamble de especies de árboles en sitios que conforman gradientes de riesgo de sequía atmosférica y edáfica, se utilizaron los métodos RLQ y ‘Fourth‐Corner’. Específicamente, nos preguntamos cómo la variación en la radiación potencial, la disponibilidad de agua del suelo y la evapotranspiración interactúan con los rasgos funcionales de las especies para explicar la distribución de especies con diferentes estrategias funcionales, las cuales van desde adquisitivas hasta conservativas, a lo largo de los gradientes de sequía. Las condiciones ambientales y los atributos funcionales estuvieron estrechamente relacionados. Contrario a lo esperado, las especies conservadoras tolerantes a la sequía, que tienen tejidos densos y hojas tardíamente caducas, fueron favorecidas en sitios con mayor disponibilidad de recursos (agua en el suelo). Las especies adquisitivas, que evitan la sequía y que tienen tejidos que almacenan agua, así como hojas delgadas, livianas y prontamente caducas, fueron favorecidas en sitios con suelos más secos. Estas aparentes discrepancias pueden explicarse por el desacoplamiento de las condiciones estresantes causadas por la aridez del suelo y la atmósfera, aunado a las diferencias en las adaptaciones de las especies a cada uno de estos factores. Síntesis. Los gradientes de estrés por sequía implicaron cambios en la composición funcional de la comunidad. Los resultados indican que la aridez atmosférica y la edáfica pueden estar desacopladas y determinar conjuntamente el ensamblaje de las especies con respecto a sus estrategias funcionales. El estrés por sequía atmosférica es un factor frecuentemente inadvertido cuando se pretende explicar el ensamblaje comunitario. Tras ponderar la relevancia de este factor ambiental, ofrecemos una explicación novedosa a un patrón aparentemente contrastante en los bosques tropicales estacionalmente secos, donde las especies con estrategias adquisitivas, en lugar de las conservadoras, predominan en ambientes con recursos más limitados pero menos demandantes de agua. En general, los resultados enfatizan la necesidad de estudios detallados que evalúen las múltiples relaciones entre el hábitat, los rasgos funcionales y el ambiente, como una estrategia para avanzar en nuestra comprensión predictiva de la distribución de especies y el ensamblaje comunitario. Atmospheric drought stress is a key yet often overlooked factor in studies of community assembly. We show that atmospheric and soil drought risks combined sort species with contrasting drought coping strategies and can explain a seemingly contrasting pattern in tropical dry forests where species with acquisitive, rather than conservative strategies, predominate in the most resource‐limited yet less water demanding environment.

Assessing the recovery of species diversity and composition after major disturbance is key to understanding the resilience of tropical forests through successional processes, and its importance for biodiversity conservation. Despite the specific abiotic environment and ecological processes of tropical dry forests, secondary succession has received less attention in this biome than others and changes in species diversity and composition have never been synthesised in a systematic and quantitative review. This study aims to assess in tropical dry forests 1) the directionality of change in species richness and evenness during secondary succession, 2) the convergence of species composition towards that of old-growth forest and 3) the importance of the previous land use, precipitation regime and water availability in influencing the direction and rate of change. We conducted meta-analyses of the rate of change in species richness, evenness and composition indices with succession in 13 tropical dry forest chronosequences. Species richness increased with succession, showing a gradual accumulation of species, as did Shannon evenness index. The similarity in species composition of successional forests with old-growth forests increased with succession, yet at a low rate. Tropical dry forests therefore do show resilience of species composition but it may never reach that of old-growth forests. We found no significant differences in rates of change between different previous land uses, precipitation regimes or water availability. Our results show high resilience of tropical dry forests in term of species richness but a slow recovery of species composition. They highlight the need for further research on secondary succession in this biome and better understanding of impacts of previous land-use and landscape-scale patterns. Synthesis Secondary forests account for an increasing proportion of remaining tropical forest. Assessing their resilience is key to conservation of their biodiversity. Our study is the first meta-analysis of species changes during succession focussing on tropical dry forests, a highly threatened yet understudied biome. We show a gradual species accumulation and convergence of composition towards that of old-growth forests. While secondary tropical dry forests offer good potential for biodiversity conservation, their capacity for recovery at a sufficient rate to match threats is uncertain. Further research on this biome is needed to understand the effect of land use history and landscape processes.

Succession is defined as a directional change in species populations, the community, and the ecosystem at a site following a disturbance. Succession is a fundamental concept in ecology as it links different disciplines. An improved understanding of succession is urgently needed in the Anthropocene to predict the widespread effects of global change on succession and ecosystem recovery, but a comprehensive successional framework (CSF) is lacking. A CSF is needed to synthesize results, draw generalizations, advance successional theory, and make improved decisions for ecosystem restoration. We first show that succession is an integral part of socio‐ecological system dynamics and that it is driven by social and ecological factors operating at different spatial scales, ranging from the patch to the globe. We then present a CSF at the local scale (patch and landscape) at which succession takes place and explain the underlying successional processes and mechanisms operating at that scale. The CSF reflects the increasingly broader perspective on succession and includes recent theoretical advances by not only focusing on species replacement but also on ecosystem development, considering succession as part of a socio‐ecological system, and taking the effect of past and current land use, the landscape context, biotic interactions, and feedback loops into account. We discuss how the CSF can be used to integrate and synthesize successional studies, and its implications for ecosystem restoration.

Biodiversity conservation and ecosystem-service provision will increasingly depend on the existence of secondary vegetation. Our success in achieving these goals will be determined by our ability to accurately estimate the structure and diversity of such communities at broad geographic scales. We examined whether the texture (the spatial variation of the image elements) of very high-resolution satellite imagery can be used for this purpose. In 14 fallows of different ages and one mature forest stand in a seasonally dry tropical forest landscape, we estimated basal area, canopy cover, stem density, species richness, Shannon index, Simpson index, and canopy height. The first six attributes were also estimated for a subset comprising the tallest plants. We calculated 40 texture variables based on the red and the near infrared bands, and EVI and NDVI, and selected the best-fit linear models describing each vegetation attribute based on them. Basal area (R(2) = 0.93), vegetation height and cover (0.89), species richness (0.87), and stand age (0.85) were the best-described attributes by two-variable models. Cross validation showed that these models had a high predictive power, and most estimated vegetation attributes were highly accurate. The success of this simple method (a single image was used and the models were linear and included very few variables) rests on the principle that image texture reflects the internal heterogeneity of successional vegetation at the proper scale. The vegetation attributes best predicted by texture are relevant in the face of two of the gravest threats to biosphere integrity: climate change and biodiversity loss. By providing reliable basal area and fallow-age estimates, image-texture analysis allows for the assessment of carbon sequestration and diversity loss rates. New and exciting research avenues open by simplifying the analysis of the extent and complexity of successional vegetation through the spatial variation of its spectral information.

We analyzed successional patterns in a very dry tropical deciduous forest by using 15 plots differing in age after abandonment and contrasted them to secondary successions elsewhere in the tropics. We used multivariate ordination and nonlinear models to examine changes in composition and structure and to estimate forest recovery rates and resilience. A shrub phase characterized early succession (0-3 yr); afterwards, the tree Mimosa acantholoba became dominant. Below its canopy, sprouts and seed-regenerated individuals of mature forest species slowly accumulated. Canopy height, plant density, and crown cover stabilized in less than 15 yr, whereas species richness, diversity, and basal area continued to increase. The pioneer species group has very low diversity and the long-lived pioneer phase typical of humid forests is absent; species composition may therefore recover soon as suggested by convergence toward mature forest species composition. The time trend of plant density also differed from humid forests for it lacked its characteristic density decline, presumably because of differences in regeneration mechanisms between very dry and other less water-stressed forest types. As opposed to the prevailing hypothesis, resilience was not higher than in moister forests, and thus factors other than structure relative simplicity must be accounted for when assessing resilience.

Mechanistic models of community assembly state that biotic and abiotic filters constrain species establishment through selection on their functional traits. Predicting this assembly process is hampered because few studies directly incorporate environmental measurements and scale up from species to community level and because the functional traits' significance is environment dependent. We analyzed community assembly by measuring structure, environmental conditions, and species traits of secondary forests in a species-rich tropical system. We found, as hypothesized, that community structure shaped the local environment and that strong relationships existed between this environment and the traits of the most successful species of the regeneration communities. Path and multivariate analyses showed that temperature and leaf traits that regulate it were the most important factors of community differentiation. Comparisons between the trait composition of the forest's regeneration, juvenile, and adult communities showed a consistent community assembly pattern. These results allowed us to identify the major functional traits and environmental factors involved in the assembly of dry-forest communities and demonstrate that environmental filtering is a predictable and fundamental process of community assembly, even in a complex system such as a tropical forest.

We tested whether and how functional composition changes with succession in dry deciduous and wet evergreen forests of Mexico. We hypothesized that compositional changes during succession in dry forest were mainly determined by increasing water availability leading to community functional changes from conservative to acquisitive strategies, and in wet forest by decreasing light availability leading to changes from acquisitive to conservative strategies. Research was carried out in 15 dry secondary forest plots (5-63 years after abandonment) and 17 wet secondary forest plots (<1-25 years after abandonment). Community-level functional traits were represented by community-weighted means based on 11 functional traits measured on 132 species. Successional changes in functional composition are more marked in dry forest than in wet forest and largely characterized by different traits. During dry forest succession, conservative traits related to drought tolerance and drought avoidance decreased, as predicted. Unexpectedly acquisitive leaf traits also decreased, whereas seed size and dependence on biotic dispersal increased. In wet forest succession, functional composition changed from acquisitive to conservative leaf traits, suggesting light availability as the main driver of changes. Distinct suites of traits shape functional composition changes in dry and wet forest succession, responding to different environmental filters.

Global plant trait studies have revealed fundamental trade-offs in plant resource economics. We evaluated such trait trade-offs during secondary succession in two species-rich tropical ecosystems that contrast in precipitation: dry deciduous and wet evergreen forests of Mexico. Species turnover with succession in dry forest largely relates to increasing water availability and in wet forest to decreasing light availability. We hypothesized that while functional trait trade-offs are similar in the two forest systems, the successful plant strategies in these communities will be different, as contrasting filters affect species turnover. Research was carried out in 15 dry secondary forest sites (5-63 years after abandonment) and in 17 wet secondary forest sites (<1-25 years after abandonment). We used 11 functional traits measured on 132 species to make species-trait PCA biplots for dry and wet forest and compare trait trade-offs. We evaluated whether multivariate plant strategies changed during succession, by calculating a 'Community-Weighted Mean' plant strategy, based on species scores on the first two PCA-axes. Trait spectra reflected two main trade-off axes that were similar for dry and wet forest species: acquisitive versus conservative species, and drought avoiding species versus evergreen species with large animal-dispersed seeds. These trait associations were consistent when accounting for evolutionary history. Successional changes in the most successful plant strategies reflected different functional trait spectra depending on the forest type. In dry forest the community changed from having drought avoiding strategies early in succession to increased abundance of evergreen strategies with larger seeds late in succession. In wet forest the community changed from species having mainly acquisitive strategies to those with more conservative strategies during succession. These strategy changes were explained by increasing water availability during dry forest succession and increasing light scarcity during wet forest succession. Although similar trait spectra were observed among dry and wet secondary forest species, the consequences for succession were different resulting from contrasting environmental filters.

Significance Although forest succession has been approached as a predictable process, successional trajectories vary widely, even among nearby stands with similar environmental conditions and disturbance histories. We quantified predictability and uncertainty during tropical forest succession using dynamical models describing the interactions among stem density, basal area, and species density over time. We showed that the trajectories of these forest attributes were poorly predicted by stand age and varied significantly within and among sites. Our models reproduced the general successional trends observed, but high levels of noise were needed to increase model predictability. These levels of uncertainty call into question the premise that successional processes are consistent over space and time, and challenge the way ecologists view tropical forest regeneration. Although forest succession has traditionally been approached as a deterministic process, successional trajectories of vegetation change vary widely, even among nearby stands with similar environmental conditions and disturbance histories. Here, we provide the first attempt, to our knowledge, to quantify predictability and uncertainty during succession based on the most extensive long-term datasets ever assembled for Neotropical forests. We develop a novel approach that integrates deterministic and stochastic components into different candidate models describing the dynamical interactions among three widely used and interrelated forest attributes—stem density, basal area, and species density. Within each of the seven study sites, successional trajectories were highly idiosyncratic, even when controlling for prior land use, environment, and initial conditions in these attributes. Plot factors were far more important than stand age in explaining successional trajectories. For each site, the best-fit model was able to capture the complete set of time series in certain attributes only when both the deterministic and stochastic components were set to similar magnitudes. Surprisingly, predictability of stem density, basal area, and species density did not show consistent trends across attributes, study sites, or land use history, and was independent of plot size and time series length. The model developed here represents the best approach, to date, for characterizing autogenic successional dynamics and demonstrates the low predictability of successional trajectories. These high levels of uncertainty suggest that the impacts of allogenic factors on rates of change during tropical forest succession are far more pervasive than previously thought, challenging the way ecologists view and investigate forest regeneration.

A complex set of interactions among neighbors influences plant performance and community structure. Understanding their joint operation requires extensive information on species characteristics and individual performance. We evaluated first-year survival of 35 719 tropical forest seedlings of 222 species and 15 annual cohorts relative to the density of conspecific and heterospecific neighbors and the phylogenetic similarity of heterospecific neighbors. Neighbors were from two size classes, and size asymmetric interactions provided insight into likely mechanisms. Large heterospecific and conspecific neighbors reduced seedling survival equally, suggesting resource competition rather than host-specific enemies as a mechanism. In contrast, much stronger negative conspecific effects were associated with seedling neighbors capable of limited resource uptake, suggesting shared pests rather than competition as the mechanism. Survival improved, however, near phylogenetically similar heterospecific neighbors, suggesting habitat associations shared among closely related species affect spatial patterns of performance. Improved performance near phylogenetically similar neighbors is an emerging pattern in the handful of similar studies.