Effects of Granivores and Herbivores on Pine Savanna Groundcover Vegetation

• Main Author: Leichty, Ellen Ruth
• Other Authors: Platt, William
• Format: Others
• Language: en
• Published: LSU 2011
• Subjects: Biological Sciences
• Online Access: http://etd.lsu.edu/docs/available/etd-01272011-133441/

Pine savannas are an endangered ecosystem and cover <2% of their former range. Although often characterized by the presence of a single tree, P. palustris, the groundcover vegetation is extremely species rich. Thus, the groundcover vegetation is the focus of conservation efforts in pine savannas. This dissertation describes how fire, patches of shrubs, winter avian granivores, winter mammalian herbivores, and an introduced climbing fern (Lygodium japonicum) affect pine savanna groundcover. The fieldwork for this dissertation was done at Camp Whispering Pines, a pine savanna that has been undergoing restoration since 1990. Biennial, prescribed fires at the beginning of the growing season are a part of the habitat restoration. Although stem production of all groups of plants except bunchgrasses was stimulated by fire, annuals were found to respond most strongly to fire. Thus frequent fires appear to increase the presence of annuals in the groundcover of pine savannas. Pine savanna vegetation is interspersed with patches of shrubs. Along the margins of shrub patches there were more annual stems and fewer bunchgrass stems. Thus, shrubs appear to increase the heterogeneity of the groundcover. Pine savannas have a diverse group of avian granivores including some rare and endemic species. Avian granivores are probably selective in the seeds that they remove. Thus, they probably change the composition of the pool of seeds available to germinate. By removal of common species or large-seeded competitive dominants, avian granivores were predicted to increase the species richness of pine savanna groundcover vegetation. The White-tailed Deer (Odocoileus virginianus) and the Eastern Cottontail (Sylvilagus virginianus) are mammalian herbivores present at the study site. Mammalian herbivores often affect plant communities by removal of competitive dominants or selective removal of woody species. Mammalian herbivory was found to decrease the numbers of bunchgrasses, but did not affect other components of the plant community. In addition, bunchgrasses showed a large increase through the five seasons of data. There were, however, no subsequent changes as a result of this increase in stem numbers. Thus, bunchgrasses do not appear to competitively exclude other members of the species-rich groundcover community. Lygodium japonicum potentially threatens pine savanna groundcover. I evaluated how shrubs and fire affect its ability to invade pine savannas. Lygodium japonicum was found to occur in many more of the experimental plots along the margins of shrubs, and fire did not decrease its biomass. Presence of shrubs appears to facilitate invasion of pine savannas by L. japonicum, and fire is not an effective method of control.