How do distinct facets of tree diversity and community assembly respond to environmental variables in the subtropical Atlantic Forest?

This study assessed the impact of altitude, precipitation, and soil conditions on species richness (SR), phylogenetic diversity (PD), and functional diversity (FD) standardized effect sizes in subtropical Brazilian Atlantic Forest tree communities. We considered specific trait information (FDs) for FD, reflecting recent adaptive evolution, contrasting with deeper phylogenetic constraints in FD. Three functional traits (leaf area-LA, wood density-WD, and seed mass-SM) were examined for their response to these gradients. Generalized least squares models with environmental variables as predictors and diversity metrics as response variables were used, and a fourth-corner correlation test explored trait-environmental relationships. SR decreased with altitude, while PD increased, indicating niche convergence at higher altitudes. Leaf area and seed mass diversity also decreased with altitude. For LA, both FD and FDs were significant, reflecting filtering processes influenced by phylogenetic inheritance and recent trait evolution. For SM, only the specific trait structure responded to altitude. LA and SM showed significant trait-environmental relationships, with smaller-leaved and lighter-seeded species dominant at higher altitudes. Soil gradients affect diversity. Fertile soils have a wider range of LA, indicating coexistence of species with different nutrient acquisition strategies. WD variation is lower for FDs. SM diversity has different relationships with soil fertility for FDs and FD, suggesting phylogeny influences trait variation. Soil pH influences WD and LA under acidic soils, with deeper phylogenetic constraints (FD). Environmental factors impact tree communities, with evidence of trait variation constraints driven by conditions and resources. Subtropical Atlantic forests' tree assemblies are mainly influenced by altitude, pH, and soil fertility, selecting fewer species and narrower trait spectra under specific conditions (e.g., higher altitudes, pH). Functional diversity patterns reflect both phylogenetic and recent evolution constraints, with varying strength across traits and conditions. These findings highlight the intricate processes shaping long-lived species assembly across diverse environments in the Southern Brazilian Atlantic Forest.

Biotic homogenization and differentiation of plant communities in tropical and subtropical forests.

Anthropogenic impacts on biodiversity can lead to biotic homogenization (BH) and biotic differentiation (BD). BH is a process of increasing similarity in community composition (including taxonomic, functional, and phylogenetic components), whereas BD is a process of decreasing similarity over space and time. Here, we conducted a systematic review of BH and BD in plant communities in tropical and subtropical forests to identify trends and knowledge gaps. Our bibliometric search in the Web of Science returned 1989 papers, of which 151 matched our criteria and were included in the analysis. The Neotropical region had the largest number of articles, and Brazil was the most represented country with 92 studies. Regarding the type of change, homogenization was more frequent than differentiation (noted in 69.6% of publications). The taxonomic diversity component was measured more often than functional and phylogenetic diversity components. Most studies (75.6%) assessed homogenization and differentiation based on a single observation in time; as opposed to few studies that monitored plant community over multiple years. Forest fragmentation was cited as the main determinant of homogenization and differentiation processes (57.2% of articles). Our results highlight the importance of evaluating community composition over time and more than taxonomic components (i.e., functional and phylogenetic) to advance understanding of homogenization and differentiation. Both processes were scale dependent and not mutually exclusive. As such, future research should consider differentiation as a potential transition phase to homogenization and that potential differences in both processes may depend on the spatial and temporal scale adopted. Understanding the complexity and causes of homogenization and differentiation is essential for biodiversity conservation in a world increasingly affected by anthropogenic disturbances.

Los impactos antropogénicos sobre la biodiversidad pueden resultar en la homogenización y diferenciación biótica. La homogenización biótica consiste en una creciente similitud de la composición comunitaria (incluidos los componentes taxonómicos, funcionales y filogenéticos), mientras que la diferenciación biótica conlleva la disminución en similitudes a lo largo del tiempo y el espacio. En este trabajo realizamos una revisión sistemática de la homogenización y diferenciación biótica en las comunidades vegetales en los bosques tropicales y subtropicales para identificar tendencias y vacíos de conocimiento. Nuestra búsqueda bibliométrica en Web of Science produjo 1989 artículos, de los cuales 151 cumplieron con nuestros criterios y fueron incluidos en el análisis. La región neotropical tuvo el mayor número de artículos y Brasil fue el país más representado con 92 estudios. Con respecto al tipo de cambio, la homogenización fue más frecuente que la diferenciación (reportada en 69.6% de las publicaciones). El componente de diversidad taxonómica se midió más veces que los componentes de diversidad funcional y filogenética. La mayoría de los estudios (75.6%) examinó la homogenización y la diferenciación con base en una sola observación en el tiempo; unos cuantos estudios sí monitorearon las comunidades vegetales a través de varios años. Se citó a la fragmentación del bosque como el principal determinante de los procesos de homogenización y diferenciación (57.2% de los artículos). Nuestros resultados resaltan la importancia de la evaluación de la composición de la comunidad a través del tiempo y más allá de los componentes taxonómicos para propiciar el entendimiento de la homogenización y la diferenciación. Ambos procesos dependieron de la escala y no se excluyeron mutuamente. Por lo tanto, las siguientes investigaciones deberían considerar a la diferenciación como una fase potencial de transición hacia la homogenización y que las posibles diferencias en ambos procesos podrían depender de la escala espacial y temporal aplicada. Son esenciales el entendimiento de la complejidad y las causas de la homogenización y la diferenciación para la conservación de la biodiversidad en un planeta que cada vez se ve más afectado por las perturbaciones antropogénicas.