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Abstract: The tropical forest carbon sink is known to be drought sensitive, but it is unclear which forests are the most vulnerable to extreme events. Forests with hotter and drier baseline conditions may be protected by prior adaptation, or more vulnerable because they operate closer to physiological limits. Here we report that forests in drier South American climates experienced the greatest impacts of the 2015–2016 El Niño, indicating greater vulnerability to extreme temperatures and drought. The long-term, ground-measured tree-by-tree responses of 123 forest plots across tropical South America show that the biomass carbon sink ceased during the event with carbon balance becoming indistinguishable from zero (−0.02 ± 0.37 Mg C ha−1 per year). However, intact tropical South American forests overall were no more sensitive to the extreme 2015–2016 El Niño than to previous less intense events, remaining a key defence against climate change as long as they are protected.

Resprouting is a plant persistence strategy in response to disturbance or stressful environmental conditions. Resprouters can dominate in stressful environments such as tropical dry forests (TDFs), but our knowledge of resprouting in TDFs is limited. Here, using a dataset of forest inventories in 16 TDF fragments (covering 15,642 trees and 321 species), we investigated patterns of resprouting in ecosystems subject to substantial seasonal water stress. We focused on two resprouting metrics: the proportion of trees that are multistemmed (resprouting frequency) and the number of stems per tree. In addition, we investigated the relative importance of environmental factors, taxonomic identity, and evolutionary history in resprouting response. Taxa with low to medium resprouting frequencies (17.19%–40.2%) are the most prevalent in TDF, compared to non‐resprouters and high‐frequency resprouters. Overall, resprouting ability appears to be an intrinsic trait that varies in response to environmental conditions but only within a range constrained by taxonomic identity. However, we found no phylogenetic signal above the genus level for any resprouting variables. Thus, the variation in resprouting across TDF lineages likely has been shaped by divergence between closely related taxa and convergence between distantly related ones, reflecting the specific environmental and disturbance factors to which they have been subjected. [ABSTRACT FROM AUTHOR]

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Species distribution patterns, community structure, and dynamics are determined on a small scale by soil and habitat heterogeneity. The aim of this work is to evaluate the temporal changes in composition and structure of a tree community, revealing the ecological drivers of the observed vegetation patterns. For 16 years (2000, 2005, 2010, and 2016) we monitored the temporal variations in structure and floristic composition of a semideciduous seasonal forest through 20 × 20 m2 (400 m2) plots, totaling 2.08 ha of sampled area encompassing Cambisol (0.4 ha), Oxysol (1.12 ha), and Nitosol (0.56 ha) soil classes. These tree communities were different in floristic and structural composition and showed oscillations over the years. The individual density and temporal beta diversity did not show differences among the soil classes in any of the monitoring intervals. In the other parameters, the Cambisols differed from the other soil classes, presenting the lowest species richness, greater floristic dissimilarity, and a structural pattern characterized by the dominance of Galipea jasminiflora (A.St.-Hil.) Engl. in all measurement years. From these results, we conclude that the temporal oscillations did not alter the original characteristics of the vegetation due to the species' adaptations to the environment, entailing the maintenance of the habitat characteristics and the directional development of the communities. [ABSTRACT FROM AUTHOR]

• Soil mediates the effects of precipitation on dry forests tree vegetation. • Precipitation seasonality decreases biomass and drives shifts in species composition. • Biomass of sites on sandy soils under strong seasonality are vulnerable to drought. • Biogeographic transitional regions can have high heterogeneity at local scales. • Local scale aspects should be included in conservation and management planning. 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. [ABSTRACT FROM AUTHOR]

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., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)