Conclusion
The size of resident species in old-field vegetation plots had a significant impact on light penetration; however, it appears that this impact is quite limited. This should be studied further, with more thorough assessments of plot-level height, to clarify the degree to which large species have the capacity to shade smaller species in herbaceous communities. Small plant species abundance and richness were significantly lower when light penetration was lower; however, this impact was once again relatively small. Our results are consistent with the results of competition experiments that reveal a size-advantage in competition, but add context by demonstrating that, in our study community, this advantage has only a very small impact on small species. Several possible explanations exist. For example, mitigating impacts on large plants, like herbivory, may reduce the capacity for large species to outcompete small species for light. It is also possible that one or more of several characteristics of small species (early season growth and reproduction, shade tolerance) contribute to greater reproductive economy of small species (Aarssen 2008). This study also adds to the sparse body of literature on the light environment in unmanipulated herbaceous plant communities.
Acknowledgments: Funding was provided by a discovery grant to LA from the Natural Sciences and Engineering Research Council of Canada (NSERC). Summer salary for GP was provided by an Undergraduate Summer Research Award from NSERC. Jennifer Waugh provided field assistance, and the staff of the Queen’s University Biological Station provided logistical support for this project. The authors declare that there is no conflict of interest.