While plant functional traits have been frequently used as a proxy for species’ life history strategies, and distributions of these traits have been used as evidence for particular mechanisms of community assembly, these tests often rely on deducing process from observed pattern. In attempting to link functional traits to coexistence mechanisms, one potential route is to consider the impact of traits on demographic performance. While certain traits have been tied to demographic performance, and while under some circumstances, demographic tradeoffs have been shown to drive coexistence, bringing these three components together in one study is novel.
In this study, we ask three questions: 1) Are traits and intraspecific variability in those traits tied to demographic performance of woody species in a temperate forest? 2) Are observed trait patterns consistent with stabilizing or fitness equalizing demographics? 3) What trait tradeoffs would be necessary to drive demographic coexistence?
To test these questions, we sampled a total of 7195 leaves from 632 individuals representing 14 species at the E.S. George Reserve in Southeast Michigan, and utilize existing 5 year census data from over 20,000 stems. Specific leaf area, leaf laminar area, and leaf dry matter content were measured and recorded for each leaf; leaf nitrogen content samples were bulked by individual.
Results/Conclusions
We found moderate correlations between growth and SLA (positive), LDMC (negative), and Leaf Laminar Area (negative); mortality increased with increasing SLA and decreased with increasing LDMC. Recruitment into the 3.18 cm dbh size class was not correlated with any of these functional traits. Plasticity and intraspecific variability levels were at best weakly correlated with any of the demographic rates.
These results suggest that functional traits can be moderately efficacious predictors of demographic parameters in some cases. The poor correlation of recruitment with these traits was somewhat puzzling, given the relatively large size of the smallest size class. Perhaps seed size and numbers dominate through more years of ontogeny than previously thought, or perhaps other forces have essentially equalized processes to that point in ontogeny. It appears that at least some trait tradeoffs surrounding growth-survivorship, in particular, may be stabilizing in this model.
