Ecologist have a long standing interest in describing species' distributions and abundances along gradients and in understanding how species attributes determine performance, but have rarely simultaneously considered all parts of this relationship. Co-considering environmental gradients, traits, and performance allows for the evaluation of trade-offs across gradients and can create a better understanding of the importance of traits during establishment. Here we evaluate the importance of trait-environment interactions during seedling establishment. Virtually all trait-based community assembly studies use data collected from communities dominated by adult individuals and infer the process of assembly. However, much of the sorting that occurs during community assembly may take place through the germination, establishment, and death of seedlings. Individuals that successfully disperse to a location may fail to establish if conditions are not conducive to germination and establishment.
To do this we utilized a large-scale prairie restoration experiment. In the first year of establishment, across 12 restoration sites, we counted the abundance of 70 sown species within five 25m2 plots at each site. Within each site we collected data on environmental conditions thought to influence seedling establishment including soil water holding capacity (WHC), light availability, soil nutrient content, and herbivore pressure. We also grew each species in the greenhouse and collected functional traits related to establishment including seed mass, growth rate, specific leaf area (SLA), and root:shoot. We asked whether trait environment interactions affected the establishment of sown prairie species within the first growing season across these sites.
Results/Conclusions
We did not find an effect of any individual trait on seedling establishment. We did however find that trait-environment interactions predicted seedling establishment rates. There was a significant interaction between SLA and herbivore pressure (p=0.03), whereby species with higher SLA occurred less frequently in plots with high herbivory rates. We also found a marginally significant interaction between SLA and soil water holding capacity (p=0.07) where all species established relatively poorly in plots with low WHC, but low SLA species established better than high SLA species on sites with high WHC. Our findings illustrate the importance of considering trait-environment interactions to understand seedling establishment and community assembly, as traits alone did not predict establishment. We also show evidence of trade-offs, as traits did not perform equally well across environmental gradients. Further consideration of trait environment interactions is required, given that we may be currently under-estimating the importance of traits, if measured independent of environment, for community assembly.