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Discrete thresholds of structural or functional decline of a vegetation type are not readily apparent, as a vegetation type can slowly decline leading to transformations in its species composition and weakened or altered functions. However, forest monitoring can be used to assess changes in ecological functions in community structure and functional and phylogenetic composition of species. This study evaluated the existence of temporal variations in the functional and phylogenetic composition of a tree community, the occurrence of heterogeneity in the behavior of phylogenetic and functional variations, and how this possible heterogeneity influences the functional and phylogenetic variations under the aspect of environmental variations and by demographic ecological processes. Results detected quantitative and qualitative changes throughout the community, such as colonization, local extinctions, in demography and biomass, and increased evolutionary distinction, lower wood density species and phylogenetic clustering. These results have shown us that the natural changes of a community should not be underestimated, because the disappearance of a community can not only occur by the direct elimination of vegetation, but can be incremental with gradual changes in its functional characteristics and species composition, transforming itself into a new community with a new combination of species and new functions., Los umbrales discretos de deterioro estructural o funcional de un tipo de vegetación no son fácilmente aparentes, ya que un tipo de vegetación puede disminuir lentamente, lo que lleva a transformaciones en la composición de sus especies y funciones debilitadas o alteradas. Sin embargo, las observaciones pueden usarse para evaluar los cambios en las funciones ecológicas antes de que esto ocurra a través de la estructura comunitaria y la composición funcional y filogenética de las especies. Este estudio evaluó la existencia de variaciones temporales en la composición funcional y filogenética de una comunidad arbórea; la ocurrencia de heterogeneidad en el comportamiento de variaciones filogenéticas y funcionales; y cómo esta posible heterogeneidad influye en las variaciones funcionales y filogenéticas bajo el aspecto de variaciones ambientales y por procesos demográficos ecológicos. Los resultados en la detección de cambios cuantitativos y cualitativos en toda la comunidad con la colonización y las extinciones locales en la comunidad, las diferencias demográficas y de biomasa, la distinción evolutiva aumentada, las especies de menor densidad de madera y el agrupamiento filogenético. Los resultados han demostrado que los cambios naturales de una comunidad no deben subestimarse, porque la desaparición de una comunidad no solo puede ocurrir por la eliminación directa de la vegetación, sino que puede ser incremental con cambios graduales en sus características funcionales y composición de especies, transformando en una nueva comunidad con una nueva combinación de especies y nuevas funciones.

In the neotropical region, seasonally dry tropical forests (SDTF) are commonly associated with scatterly distributed limestone outcrops, known for harbouring high numbers of endemic species and genera. In the context of lacking knowledge on fine-scale vegetation and environmental heterogeneity of these geoecosystems and having a limestone outcrop in eastern Brazil as a case study, we address the question: how important are limestone outcrops for SDTF tree community composition, structure, function and evolution? We distinguished five habitats related to position and distance to the outcrop, and within each of 25 sampled plots (five per habitat), we identified and measured the diameter of all living tree individuals and collected soil samples for chemical and textural analyses. We investigated taxonomic and phylogenetic substitution across the habitats and fitted linear models to test the effects of habitat type, soil fertility and texture on taxonomic/structural, functional and phylogenetic parameters. We found striking taxonomic and phylogenetic differentiation among the habitats, especially related to recent diversification, with soil fertility and texture largely accounting for variations in all analysed parameters. Given the predominant roles of vicariance and in situ diversification believed to have given rise to the current patterns of endemism and diversity of eastern Brazil SDTF, we argue that the conditions presented by limestone outcrops, including aridity and high fertility, may have favoured the persistence of SDTF lineages during the Quaternary environmental changes, highlighting their role as litho-refugia. In order to complete this biogeographic puzzle, we encourage other fine-scale assessments of outcrop-associated SDTF from the phylogenetic viewpoint.

Our work aimed to test the hypothesis that soil microscale heterogeneity act as a community ecological driver, increasing diversity and promoting structural shifts on the Seasonally Dry Tropical Forest (SDTF) tree community. We evaluated the relationship between microscale edaphic variations and floristic–structural patterns of tree communities in a SDTF fragment located in the southern end of the Brazilian Caatinga domain. Vegetation and soil data were obtained through 27 sample units of 400 m2 (20 m × 20 m), within each one we measured and identified at species level all arboreal individuals with Circumference at the Breast Height greater or equal to 10 cm, and also collected the soil samples. Through the data we evaluated soil variation influence on the tree community structural and floristic patterns trough generalized linear models. Soil explained the small-scale structural and floristic variations, contributing significantly to biomass, sprouting and to floristic relationships between sample units. It was also observed a possible relation of the result with the Caatinga domain biogeographic history, due the presence of Sedimentary Caatinga species, which are not expected for the study region. Soil plays an important role in driving small-scale complexity and diversity of SDTF, but we also suggest that Caatinga biogeographic events have influence on the high heterogeneity patterns.

Tropical forests have played an important role as a carbon sink over time. However, the carbon dynamics of Brazilian non-Amazon tropical forests are still not well understood. Here, we used data from 32 tropical seasonal forest sites, monitored from 1987 to 2020 (mean site monitoring length, ~15 years) to investigate their long-term trends in carbon stocks and sinks. Our results highlight a long-term decline in the net carbon sink (0.13 Mg C ha-1 year-1) caused by decreasing carbon gains (2.6% by year) and increasing carbon losses (3.4% by year). The driest and warmest sites are experiencing the most severe carbon sink decline and have already moved from carbon sinks to carbon sources. Because of the importance of the terrestrial carbon sink for the global climate, policies are needed to mitigate the emission of greenhouse gases and to restore and protect tropical seasonal forests.

Resprouting is an ecological strategy widely adopted by trees in response to different restrictive factors, in which the stems can be emitted at different heights of the tree. Although the patterns of resprouting height are already known in response to some restrictive factors (such as fire), their occurrence is not well elucidated in non-fire prone dry environments where continuous resource restriction may stimulate resprouting. Here, we assessed the general ecological dominance of resprouting trees in the community and the ecological dominance of trees resprouting at different heights in response to environmental restrictions in a tropical dry forest (TDF). We used multi-stemmed trees as a proxy for resprouting in response to the local restrictive factors. Our hypotheses were: i) resprouting trees have greater ecological dominance (more trees and stems and higher biomass) in more restrictive plots; ii) the ecological dominance of lower-height resprouting trees is greater in more restrictive plots, while the dominance of upper-height resprouting trees is greater in less restrictive plots. For this, we used a dataset of 27 TDF plots where we measured and identified the trees that met the inclusion criterion (3 cm of diameter at breast height) and collected soil samples to gather data on environmental restriction. Multi-stemmed trees were classified according to the height of additional-stem emission (below-ground, ground-level, and above-ground), considering the bottom-most stem originating from the main stem. We then evaluated whether the ecological dominance of resprouting trees and trees with different resprouting heights varied significantly in response to environmental restrictiveness, and patterns of species composition in the height categories. We found a greater dominance of resprouting trees in more restrictive environments, with lower-height resprouting trees dominating the most restrictive plots (two hypotheses confirmed). This finding may be associated with physiological mechanisms of drought response because resprouting height is directly associated with the level of damage inflicted on the internal structure of trees. We also found that the species varied in their ability for stem emission at different heights, whereby the most plastic species were more dominant compared to those with just one height of emission. This finding indicates that different restrictive factors can produce similar resprouting expressions, reinforcing the need to advance the knowledge on the importance of resprouting in TDF.

Forest dynamics are driven by a myriad of factors and link directly to ecosystem services. The dynamics of the highly degraded Brazilian Atlantic Forest (AF) hotspot is mostly driven by its anthropogenic context. Currently, most of the AF region is composed of small disturbed secondary forest fragments that have received partial or full environmental protection with recent environmental norms. Such protection prevents further disturbances and consequently shifts the course of forest dynamics and ecosystem services in AF. Here, we assess long-term forest dynamics trends of a small secondary AF fragment to test the hypothesis that disturbed AF fragments are reaching advanced successional stages. We used a unique dataset of 126 permanent subplots (totaling 5.04 ha) monitored for 30 years (8 inventories between 1987 and 2017) of a disturbed secondary AF fragment (6.35 ha) that has been fully protected since 1986. In each inventory, we measured all living trees with a diameter at breast height (DBH) ≥ 5 cm and counted survivors, recruits and dead individuals between intervals. We monitored the temporal trends of (i) structural variables (biomass, tree density and species richness), (ii) functional composition (wood density and maximum potential size), (iii) and species dominance. Our results indicate that, now under full protection, the fragment is shifting towards a late successional stage: we observed increasing biomass, decreasing tree density (self-thinning) and increasing abundance of late-successional species with conservative strategies. Species richness and dominant species composition were stable throughout the monitoring period, suggesting an absence of substantial changes in community assembly. These results underscore the role played by small secondary AF fragments in ecosystem service provision (e.g., carbon uptake and shelter for biodiversity) and point to their forest dynamics trends.

The resilience or sensitivity of seasonally dry tropical forests (SDTF) to climate change remains an important issue because of their biodiversity and ecosystem services provision. Understand the underlying ecological processes of SDTF is crucial for the development of conservation and management strategies. We tested the hypotheses that SDTF tree species richness, above-ground woody biomass (AGWB), species and phylogenetic compositions are related to climate, soil and their interactions. We sampled 16 old-growth forest sites (313 plots) of SDTF within a 290 km latitudinal gradient. The sites are located in the transition zone between Caatinga and Cerrado biogeographic domains, and are near from Atlantic domain (~100 km). In each site we collected data on vegetation (trees with diameter at breast height ≥3 cm) and soil, and obtained climate data from WorldClim. Almost all vegetation attributes were significantly related to climate and soil. Soil texture mediated the effects of precipitation for tree species richness, AGWB and phylogenetic composition. Tree species richness decreases with annual precipitation but increases under less seasonal conditions; water availability leads to increases in AGWB and drives changes in both taxonomic and phylogenetic composition in these environments. Our findings indicate that tree species richness, above-ground woody biomass, taxonomic and phylogenetic composition of SDTFs are, in general, vulnerable to drought events even from local to regional scales and show the importance of local-scale aspects to understand SDTF diversity and ecosystem functioning; and provide useful information for conservation and management strategies.