Mixed effects of climate and species richness on aboveground carbon stock in subtropical Atlantic forests.

Tropical forests are global biodiversity hotspots and are crucial in the global carbon (C) cycle. Understanding the drivers of aboveground carbon stock (AGC) in a heterogeneous and biodiverse system can shed light on the processes underlying the relationship between biodiversity and carbon accumulation. Here, we investigate how biodiversity, environment, and landscape structure affect AGC. We examined such associations in 349 plots comprising over 95,346 km2 the Atlantic Forest of southern Brazil, encompassing three forest types: Dense Ombrophylous Forest (DF), Mixed Ombrophylous Forest (MF), and Seasonal Deciduous Forest (SF). Each plot was described by environmental variables, landscape metrics, and biodiversity (species richness and functional diversity). We used diversity, environmental, and landscape variables to build generalized linear mixed models and understand which can affect the forest AGC. We found that species richness is associated positively with AGC in all forest types, combined and separately. Seasonal temperature and isothermality affect AGC in all forest types; additionally, stocks are positively influenced by annual precipitation in SF and isothermality in MF. Among landscape metrics, total fragment edge negatively affects carbon stocks in MF. Our results show the importance of species diversity for carbon stocks in subtropical forests. The climate effect was also relevant, showing the importance of these factors, especially in a world where climate change tends to affect forest stock capacity negatively.

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.

Spatial and temporal structure of diversity and demographic dynamics along a successional gradient of tropical forests in southern Brazil.

Analysis of the structure, diversity, and demographic dynamics of tree assemblages in tropical forests is especially important in order to evaluate local and regional successional trajectories.We conducted a long-term study to investigate how the structure, species richness, and diversity of secondary tropical forests change over time. Trees (DBH ≥ 5 cm) in the Atlantic Forest of southern Brazil were sampled twice during a 10-year period (2007 and 2017) in six stands (1 ha each) that varied in age from their last disturbance (25, 60, 75, 90, and more than 100 years). We compared forest structure (abundance and basal area), species richness, alpha diversity, demographic rates (mortality, recruitment, and loss or gain in basal area), species composition, spatial beta diversity, and temporal beta diversity (based on turnover and nestedness indices) among stand ages and study years.Demographic rates recorded in a 10-year interval indicate a rapid and dynamic process of species substitution and structural changes. Structural recovery occurred faster than beta diversity and species composition recovery. The successional gradient showed a pattern of species trade-off over time, with less spatial dissimilarity and faster demographic rates in younger stands. As stands grow older, they show larger spatial turnover of species than younger stands, making them more stochastic in relation to species composition. Stands appear to split chronologically to some extent, but not across a straightforward linear axis, reflecting stochastic changes, providing evidence for the formation of a nonequilibrium community. Policy implications. These results reiterate the complexity and variability in forest succession and serve as a reference for the evaluation and monitoring of local management and conservation actions and for defining regional strategies that consider the diversity of local successional trajectories to evaluate the effectiveness of restoration measures in secondary forests of the Atlantic Forest biome.

Forest structure and species composition along a successional gradient of Lowland Atlantic Forest in Southern Brazil / Estrutura e composição ao longo de um gradiente sucessional de Floresta de Terras Baixas no sul do Brasil

The Lowland Forest is one of the most disturbed and fragile ecosystems in the Atlantic Forest biome, yet little is known regarding its successional trajectory and resilience. We evaluated changes in species assemblages and forest structure of the canopy and understory along a successional gradient (young 21-yrs old forest, immature 34-yrs old forest and late successional 59-yrs old forest) aiming to assess changes in species composition and successional trajectory of different strata of secondary forests. A 0.1 ha plot (ten 10x10 m sub-plots) from each forest stand was surveyed for trees and shrubs with a diameter at breast height (DBH) ≥ 4.8 cm (canopy) and for individuals with heights ≥ 1 m and DBH < 4.8 cm (understory). A total of 3,619 individuals from 82 plant species were sampled. The successional gradient was marked by a unidirectional increase in species richness and a bidirectional pattern of density changes (increasing from young to immature forest and decreasing from immature to late successional forest). Community assemblages were distinct in the three forests and two strata; indicator species were only weakly shared among stands. Thus, each successional forest and stratum was observed to be a unique plant community. Our results suggest slight predictability of community assemblages in secondary forests, but a relatively fast recovery of forest structure.

As Florestas de Terras Baixas constituem um dos ecossistemas mais perturbados e frágeis no bioma Mata Atlântica, mas ainda pouco se sabe sobre sua trajetória sucessional e resiliência. Foram avaliadas alterações na composição de espécies e a estrutura florestal do dossel e sub-bosque ao longo de um gradiente sucessional (floresta jovem-21 anos, floresta imatura-34 anos, floresta madura-59 anos) com o objetivo de verificar as mudanças na composição de espécies e a trajetória sucessional de diferentes estratos destas florestas secundárias. Uma parcela de 0,1 ha (dez sub-parcelas de 10x10 m) foi estabelecida em cada floresta, amostrando-se árvores e arbustos com um diâmetro è altura do peito (DAP) ≥ 4,8 cm (dossel) e para indivíduos com altura > 1 m e DAP < 4,8 cm (sub-bosque). Um total de 3.619 indivíduos de 82 espécies de plantas foram amostrados. O gradiente sucessional foi marcado por um aumento unidirecional na riqueza de espécies com o tempo, e um padrão bidirecional de mudanças de densidade (aumentando da floresta jovem para a imatura e diminuindo da imatura para a madura). As assembléias de plantas eram distintas nas três florestas e nos dois estratos; espécies indicadoras foram pouco compartilhadas entre as florestas. Portanto, cada estádio da cronosequência e cada estrato representam uma comunidade única de plantas. Nossos resultados sugerem pouca previsibilidade das assembleias de plantas destas florestas secundárias, mas uma recuperação relativamente rápida da estrutura da floresta.

Ant-diaspore interactions during secondary succession in the Atlantic forest of Brazil

Animal-plant interactions are important for the recovery of diversity and processes in secondary forests, which increasingly dominate the tropical landscape. We used a combination of observational and experimental approaches to study the interactions of ants with diaspores across a successional gradient of forests in Southern Brazil, from August 2007 to April 2008. In addition to diaspore removal rates, we assessed the species richness, diversity and behaviour of ants interacting with diaspores, in three replicated sites of four successional stages of forests. We recorded 22 ant species interacting with diaspores (an estimated 15% of the total species pool in the region). Species richness and diversity did not differ among successional stages but the behaviour of ants towards diaspores changed with the age of secondary forests. In old successional stages the removal of entire diaspores was more common than in young successional stages of forests. Concordantly, diaspore removal rates were lowest in the youngest successional stage of secondary forests and increased with the age of forests. These results indicate that ant-diaspore interactions in secondary forests are disturbed and lower removal rates in secondary forests are likely to constrain the recruitment of plant populations during secondary succession. Rev. Biol. Trop. 60 (2): 933-942. Epub 2012 June 01.

Las interacciones entre animales y plantas son importantes para la recuperación de la diversidad y los procesos en los bosques secundarios, los cuales cada vez más tienden a dominar el paisaje tropical. Nosotros utilizamos una combinación de métodos experimentales y observaciones para estudiar las interacciones entre hormigas y diásporas a través de un gradiente de sucesión en los bosques del sur de Brasil, entre agosto 2007 y abril 2008. Además de las tasas de eliminación de diásporas, evaluamos la riqueza de especies, la diversidad y el comportamiento de las hormigas que interactúan con las diásporas, con tres repeticiones por sitio de cuatro estadios de sucesión del bosque. Se registraron 22 especies de hormigas que interactúan con diásporas (se estima un 15% del total de especies en la región). La riqueza y diversidad de especies no varió entre las etapas de sucesión, pero el comportamiento de las hormigas hacia las diásporas cambio con la edad de los bosques secundarios. En las etapas sucesionales avanzadas del bosque la eliminación de diásporas fue más común que en las etapas tempranas. En concordancia, las tasas de eliminación de diásporas fueron menores en la etapa más temprana de la sucesión de bosques secundarios y aumenta con la edad de los mismos. Estos resultados indican que las interacciones hormigasdiásporas en los bosques secundarios son alteradas y las menores tasas de extracción en los bosques secundarios es probable que limiten el reclutamiento de las poblaciones de plantas durante la sucesión secundaria.

Ant-diaspore interactions during secondary succession in the Atlantic forest of Brazil.

Animal-plant interactions are important for the recovery of diversity and processes in secondary forests, which increasingly dominate the tropical landscape. We used a combination of observational and experimental approaches to study the interactions of ants with diaspores across a successional gradient of forests in Southern Brazil, from August 2007 to April 2008. In addition to diaspore removal rates, we assessed the species richness, diversity and behaviour of ants interacting with diaspores, in three replicated sites of four successional stages of forests. We recorded 22 ant species interacting with diaspores (an estimated 15% of the total species pool in the region). Species richness and diversity did not differ among successional stages but the behaviour of ants towards diaspores changed with the age of secondary forests. In old successional stages the removal of entire diaspores was more common than in young successional stages of forests. Concordantly, diaspore removal rates were lowest in the youngest successional stage of secondary forests and increased with the age of forests. These results indicate that ant-diaspore interactions in secondary forests are disturbed and lower removal rates in secondary forests are likely to constrain the recruitment of plant populations during secondary succession.