Title

Ecological Dynamics of Native Bottomland Pecan Communities in the Edwards Plateau of Texas

Document Type

Thesis

Comments


Presented to the Graduate Council of Texas State University–San Marcos in Partial Fulfillment of the Requirements for the Degree Master of Science, May 2008.

Committee Members Approved:
Dr. Thomas R. Simpson
Dr. John T. Baccus
Dr. Floyd Weckerly
Dr. T. Wayne Schwertner

Approved:
J. Michael Willoughby, Dean of the Graduate College

Abstract

Native bottomland pecan (Carya illinoiensis) communities exist as fragments along river systems of the Edwards Plateau. They persist in this sub-humid rangeland environment because of the unique hydrologic regime of the riparian zone. Bottomland sites are currently dominated by an over story of mature pecan trees with little woody understory or replacement pecan seedlings. The lack of pecan recruitment might result in the loss of these native bottomland pecan communities as adult trees senesce and die. Objectives of my study were to: 1) determine the extent of change in these communities over several decades, 2) assess current age structure of these communities, 3) assess impact to recruitment due to herbivory and grove management, and 4) construct a computer-based conceptual model of community behavior to identify factors having the potential to affect native pecan bottomlands. Sites were selected based on species composition, accessibility, herbivore pressure, and management history (natural, harvested, harvested/groomed). Twenty pecan trees from each site were cored and cores were sent to a dendrochronology lab for aging. Results show that these pecan communities have changed little in size over the past 60 years. These communities exist primarily as mature trees with few younger age classes. Deer densities are extremely high within these communities indicating that herbivory is likely influencing recruitment rates. Computer simulation modeling identified factors affecting recruitment and mortality of native pecan trees in bottomland communities.