Successional Growth Dynamics of Woody Saplings in Tropical Dry Forest Understory

Abstract

Thoroughly understanding tropical forest secondary succession requires insights into the processes occurring in the forest understory, the vegetation component where the regenerating community develops. Although sapling growth is essential to this process, information on how it changes along succession is scarce. Here, we examine relative growth rates (RGR) of woody species saplings along a broad successional gradient in a tropical dry forest based on height and basal area data gathered over 15 years of vegetation monitoring in permanent plots differing in successional age (1–73 years) plus a mature forest plot. We used mixed-effects models to examine the link between individual size, fallow age, and plant traits, and from this link model their relationship with sapling RGR. Despite sizable RGR variability, growth was generally slow over the successional gradient, except in the first 10 years of succession, when growth rates were highest for most groups. Species' successional guild and their identity as members of the Leguminosae family were the main factors responsible for growth in basal area, while for growth in height, the main factors involved were successional guild and growth form. A generalized decrease in sapling growth rates in the understory suggests that this process is increasingly limited by light rather than by water towards later successional stages. Enhanced knowledge of the dynamics of the regenerating community in tropical dry forests is fundamental for gaining a comprehensive view of their recovery.