Department Chair

I. Martha Skerrett, Chair and Associate Professor of Biology

Date of Award


Access Control

Open Access

Degree Name

Biology, M.A.


Biology Department


Robert J. Warren II, Ph.D., Assistant Professor of Biology

Department Home page

First Reader

Daniel L. Potts, Ph.D., Associate Professor of Biology

Second Reader

Amy M. McMillan, Ph.D., Associate Professor of Biology


Recruitment success determines the abundance and composition of plant communities. Successful recruitment can be summarized as a simple dichotomy of establishment versus seed limitations. Establishment limitation occurs when plant populations are inhibited by habitat availability and quality, whereas seed limitation occurs when seeds fail to arrive in necessary densities. Recruitment failure undermines overstory sustainability if the existing trees cannot replace themselves. Preliminary analysis indicated tree recruitment failure at an urban nature preserve with too few tree seedlings to replace mature canopy trees. These data suggested that the urban forest was not sustainable. The overarching goal of the study was to test whether establishment or seed limitation explained the recruitment failure. Given that 90% of seeds are killed by unsuitable habitat conditions it was hypothesized that establishment limitation would best explain the limited recruitment. This hypothesis was tested using field experiments with introduced native tree seeds. However, environmental limitations are of little consequence if the seeds fail to arrive. This alternative hypothesis was tested using seed traps to capture dispersed seeds. Seedling recruitment varied by tree species, and it increased significantly with herbivore/granivore exclusion in experimental plots. Seed rain correlated significantly with immediately proximate parent plants, but seeds from species beyond 50 m of the experimental plots were not present in seed traps. These results suggested that habitat quality, particularly granivory and competition, limited recruitment at local scales in the urban forest whereas long-distance dispersal limited seed availability beyond local species.