Different heights of resprouting by trees: response to small-scale environmental restrictions in a non-fire-prone Caatinga tropical dry forest

Abstract

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.