Flexible demographic strategies promote the population persistence of a pioneer conifer tree (Pinus massoniana) in ecological restoration

Abstract

Understanding how plant species are able to persist in temporally variable environments is a fundamental goal in ecology. According to the demographic buffering hypothesis (DBH), organisms persist by minimizing variation over time in those vital rates (survival, growth, and/or reproduction) which affect the population growth rate the most. Alternatively, the demographic lability hypothesis (DLH) posits that a population could instead track and benefit from environmental fluctuations, by adjusting one or more of its vital rates accordingly, to maximize fitness. Empirical evidence has been found for and against each hypothesis, yet rarely are both tested in tandem for pioneer tree species, which may be the most responsive or vulnerable to environmental stochasticity in the course of forest restoration. Here we evaluated the stochastic population growth rate (λs) of Pinus massoniana, a pioneer conifer tree, using integral projection models (IPMs) applied to five plots spanning distinctive stages along early ecological restoration in Southeast China. We assessed the demographic strategy operating in each plot through an elasticity analysis and uncovered the sources of variability in these demographic strategies across plots. We found that the ca. 40-year stand populations of P. massoniana were stable or growing (i.e., λs ≥ 1) in most plots, but strategies shifted between demographically labile and buffer across plots, which was predominately driven by among-plot variation in reproduction. Our findings suggest that diverging demographic strategies may promote the persistence of pioneer tree species of P. massoniana and others similar to it during the ecological restoration of subtropical forests.