Traits mediate a tradeoff in seedling growth response to light and conspecific density in a diverse subtropical forest

Understanding tree species responses to biotic and abiotic factors is
fundamental for stronger predictions of community assembly and dynamics.
However, several challenges remain. These include a failure to investigate
whether there is evidence for key hypothesized life-history tradeoffs and
to link these tradeoffs to functional traits. In this study, we seek to
explicitly address the above outstanding challenges by constructing models
for individual seedling growth in response to abiotic and biotic factors
using three years of seedling census data from a 20-ha subtropical forest
dynamics plot in a diverse subtropical forest and correlated these
responses with functional traits. We found that light and conspecific
neighbours increase and decrease the relative growth rate of tree
seedlings, respectively. We also found that the ability of a species to
positively respond to canopy openness trades off against susceptibility to
CNDD. This tradeoff was evident across seasons and could be predicted on
functional trait - stem and leaf dry matter content. Synthesis. Our
findings indicate species that can grow quickly in high light environments
also tend to suffer more conspecific negative density dependence. The
results highlight strong evidence of a tradeoff relating to growth and
defence widely hypothesized to be of importance in diverse tree
communities and that this tradeoff occurs across seasons and can be linked
to a commonly measured functional trait.