Structural, chemical and growth variations of the woody of species distributed along a neotropical seasonal gradient (evergreen forest-savannah-dry forest) and their relationships with climate change

Tropical forests are important providers of ecosystem services and climate regulators. Among them, seasonal forests play a key role as a seasonal carbon sink, modulated by temperature and precipitation. Despite this, little is known about how interannual climate variability affects tree growth and wood structure and how climate growth responses vary across rainfall gradients in these forests. Here we evaluated changes in climate sensitivity of tree growth, various chemical-physical wood traits within 8 cm diameter size classes (SCI), as well as constructed projections of future wood growth and yield after programmed cutting cycles along an environmental gradient of seasonally dry tropical vegetation types (evergreen forest – savannah – dry forest) in Northeast Brazil, using congeneric species from two common Neotropical genera: Aspidosperma and Handroanthus. We constructed tree ring width chronologies for each combination of species × forest type and explored how growth variability correlated with local (precipitation, temperature) and global (El Niño Southern Oscillation - ENSO) climatic factors. We also evaluated how the sensitivity of growth to climate and the presence of growth deviations varied along the gradient. Through the chronologies we calculated the SCI and quantified its changes in the water use efficiency (iWUE) over time, relationship with wood structure and chemistry, in addition to the differences between different forest types. We also calculated aspects related to the cumulative diameter, the growth trajectory of the trees along the gradient and their yield after two cutting cycles. Our results reveal a dominant effect of precipitation on tree growth in seasonally dry tropical forests and suggest that along the gradient, dry forests are the most sensitive to water deficit. The negative relationship of temperature and ENSO with growth were similar between sites, however, negative growth deviations were observed mainly in dry forest species. In contrast, temperature and ENSO positively influenced iWUE, which increased over time in all seasonal forests, regardless of forest type, and had no effect on growth. In the dry forest, the variation in the iWUE of A. multiflorum was significantly related to the frequency of vessel elements in the xylem and the concentration of Fe, S and K/Ca, showing the importance of using more than one strategy to withstand stress. water in dry forests. In this sense, the dry forest species showed the lowest growth in relation to their congeners of other forest types, with different extraction limits between the congeners of Aspidosperma and Handroanthus. Only A. castroanum (evergreen forest) presented a yield close to considerable sustainable (~80%), while the other species had a low average yield, between 10-30%. These results highlight the importance of understanding the climate sensitivity of different tropical forests. Understanding the impact of water scarcity on the productivity of seasonal forests and their strategies to support it can help to understand the future carbon cycle and serve as a basis for measures to mitigate climate change. These differences show that the type of forest management must take into account the socio-environmental variations along forest gradients and that dry forests are the ones that take the longest to recover after management. This understanding is critical to predicting carbon dynamics in tropical regions, and differences in sensitivity must be considered when prioritizing conservation measures for seasonally dry topical forests (AU)