Topography influences the tree dynamics of a tropical dry forest in western Mexico

Abstract

In seasonally dry tropical forests (SDTF's) drought risk driven by topography-related factors determines vegetation structure, functional composition, and species diversity; however, the effect of slope aspect and topographic position on tree community dynamics are still poorly explored. In this paper, we studied the dynamics and structural attributes of the tree community of a Mexican SDTF. Plots were established in a combination of two topographic conditions: slope aspect (north/south) and topographic position (upper/middle/lower). Differences among these conditions were assessed through (i) community dynamics´ parameters, (ii) species dynamics, (iii) vegetation structure, and (iv) species diversity. We analyzed community attributes for each of our study years (2012–2020) and rates of change between this period for the entire community (DBH ≥1 cm), small-sized trees (DBH ≤3 cm), and large-sized trees (DBH >3 cm). Multivariate analyses were also used to examine the relationship between vegetation and topography. In upper positions, trees showed higher mortality (mean mr ± SE = 3.1 ± 0.2% yr − 1) and lower recruitment rates (mean rr ± SE = 6.3 ± 0.9% yr − 1) than those from the lower positions (mean mr ± SE = 1.7 ± 0.1% yr − 1; mean rr ± SE = 7.7 ± 0.7% yr − 1). The relative change (%) in the number of individuals for the entire community and small-sized trees increased towards the lower positions. The entire community showed a temporary loss of stems on south-facing slopes, but temporary gains in number of stems in lower positions for the small-sized trees. We did not find any temporary changes in species diversity attributes. The drought risk gradient imposed by topographic position influences the tree dynamics with a higher mortality of stems/individuals towards upper positions, but species diversity was maintained.