Author ORCID Identifier
Year of Publication
Doctor of Philosophy (PhD)
Arts and Sciences
Dr. Scott K. Gleeson
Dr. John J. Cox
Terrestrial plant communities are shaped by competition for resources, herbivory, and abiotic processes. Savanna systems represent a dynamic coexistence of contrasting life forms (grasses and trees) shaped by competition and disturbance. The Kentucky Inner Bluegrass Savanna-Woodland (KIBSW) is described as an open woodland of shade intolerant species; however, climatic, and edaphic conditions can support closed-canopy forest. After European pioneer settlement (c1750-1800), over 99% of “savanna-woodlands” have been lost. KIBSW remnants are experiencing a recruitment failure, leading to a dominance shift in tree communities. I researched how tree-grass competition and mammalian herbivory influence KIBSW regeneration and maintenance. The KIBSW does not have an intact reference system, a necessary requirement for restoration ecology. Therefore, I experimentally “rebuilt” the community by reintroducing a species pool and implementing a hypothesized disturbance regime at the best remaining example of KIBSW—Griffith Woods Wildlife Management Area, KY, USA. I established a long-term experiment on twelve species of planted tree seedlings (5760 seedlings total; 480 seedlings/sp.), representing three shade tolerance categories. Experimental treatments manipulated levels of competition (via mowing and herbicide) and herbivory (via individual seedling protectors). I collected data on individual seedling species trait-based and performance-based responses by measuring seedling survival, growth, mammalian herbivory, leaf anatomy, and ecophysiology. I reviewed factors hypothesized to influence KIBSW regeneration and maintenance by distinguishing the top-down vs. bottom-up factors that regulate plant communities. I then investigated whether competitor and herbivore reduction influenced survival and growth of tree seedlings. First year survival increased with herbivory protection; over five years, survivorship and diameter growth increased with competition reduction. Height growth increased with both competition and herbivory reduction. Species responded variably to treatments, but all increased in biomass (survival x growth) and employed either a fast or slow growth-rate strategy regardless of competition treatment. I next characterized how mammalian herbivory impacted seedling species in response to the experimental treatments. Deer herbivory was altered by the competition treatment and season. Rabbit herbivory was influenced by protector treatment and initial year, and increased rabbit herbivory reduced seedling survival and growth. Rodent herbivory was impacted by both protector and competition treatment but showed no seasonal or yearly patterns. All herbivore types exhibited tree browse preferences. Finally, I examined how tissue allocation and photosynthesis responded to the competitive environment. I predicted that within species sun leaves would be smaller, thicker, have higher photosynthesis, and higher N content compared to shade leaves. Between species I predicted that shade intolerant species would be more plastic than shade tolerant species in response to light environment. Sun/shade leaf predictions were supported; sun/shade morphological plasticity existed both within and between species. Tissue N was positively correlated to maximum photosynthetic rates, and maximum photosynthetic rates were positively correlated with survival and growth. Tissue N concentration was positively correlated with increased rates of deer herbivory, and highly preferred browse species had higher concentrations of leaf N. This research indicates that KIBSW regeneration and maintenance depends on individual species growth and survival responses to competition and herbivory, with a strong trade-off between growth allocation (via tissue N) and exposure to herbivory. The growth-herbivory trade-off is one of the potential factors contributing to KIBSW species variability in community assembly patterns.
Digital Object Identifier (DOI)
2019 Ribble Pilot Grant, University of Kentucky, Department of Biology.
2011-2016 Ribble Summer Research Grant, University of Kentucky, Department of Biology
2010-2019 Graduate Teaching Assistantship. University of Kentucky, Department of Biology.
2011, 2013 G. Flora Ribble Research Fellowship, University of Kentucky, Department of Biology.
2012 Kentucky Native Plant Society, Graduate Research Award.
2010-2016 University of Kentucky Cooperative State Research, Education, and Extension Service Grant
Shaffer, James D., "COMPETITION AND HERBIVORY INFLUENCE THE SURVIVAL, GROWTH, AND PHYSIOLOGY OF NATIVE TREE SEEDLINGS IN THE KENTUCKY INNER BLUEGRASS SAVANNA-WOODLAND" (2023). Theses and Dissertations--Biology. 93.