Elevational shifts in tree community composition in the Brazilian Atlantic Forest related to climate change

Abstract

Question: Climate change induces shifts in species distributions, ultimately changing community composition. Mountains are especially sensitive to climate change, and tree species are predicted to move towards higher elevations, but observed changes are not always unidirectional. The diversity and complexity of tropical and subtropical systems limits our understanding of climate-induced responses of subtropical mountain forests. Here, we investigated migration trends in tree community composition along an elevational gradient, and between the transition from lowland to montane forests in subtropical forests. Location: Brazilian Atlantic Forest. Methods: We used thermal affiliations of 627 tree species to calculate community temperature scores (CTS) for different life-history stages of trees in 96 permanent plots. We compared CTS of different life-history stages across space and time. Results: Most tree communities (58%) did not show a significant difference of CTS between life-history stages, indicating a non-migration trend. On the other hand, 27% of tree communities showed upward migration and 15% downward migration. Upward migration was more common in montane forests, and downward migration in lowland forests. Our temporal analysis shows significant changes in CTS values for juvenile communities with 0.36°C decrease in lowland forests and 0.34°C increase in montane forests. Conclusions: Contrasting results between lowland and montane forest communities indicate that the transition zone influences migration patterns and may reflect differences in species’ thermal limitations, as well as by non-thermal factors such as biotic interactions. Our findings provide the first evidence of climate change-induced community shifts in the Brazilian Atlantic Forest. We demonstrated that upward migration trends were predominantly observed in montane–upper mountain forests, while downward migrations were noted in lowland–submontane forests. The thermophilization of montane forests may suggest an increased risk of reduction for cold-demanding species under climate change scenarios.