Date of Award
5-2016
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Legacy Department
Forest Resources
Committee Member
Dr. G. Geoff Wang, Committee Chair
Committee Member
Dr. Saara J. DeWalt
Committee Member
Dr. Donald L. Hagan
Committee Member
Dr. Julia L. Kerrigan
Committee Member
Dr. William C. Bridges
Abstract
Laurel Wilt Disease (LWD) has caused severe mortality in native Persea species of the southeastern United States since it was first detected in 2003. This study was designed to document the range-wide population impacts to LWD, as well as the patterns of mortality and regeneration in Persea ecosystems. I used Forest Inventory and Analysis (FIA) data from the U.S. Forest Service to estimate Persea borbonia (red bay) populations from 2003 to 2011 to see if any decline could be observed since the introduction of LWD causal agents. Population estimates from 2003 to 2011 suggest that the population is declining. The population in Georgia significantly decreased from ca. 241.1 ± 11.9 million stems in 2003 to ca. 150.3 ± 7.9 million in 2011. Red bay densities decreased significantly in plots surveyed before and after the reported infection by an average of 89.6 live red bay stems/ha. I developed a logistic regression model to predict the probability of red bay mortality due to LWD. Number of years since LWD infection was the most significant variable, with every increase in 1 year resulting in a 153.7 % increase in odds of death. Diameter was also a significant predictor, with an increase of 1 cm DBH resulting in a 5.0 % increase in odds of death. To document the stand characteristics of red bay and swamp bay (Persea palustris) communities, I analyzed data collected from 1988-2012 by the Carolina Vegetation Survey. We used cluster analyses and species indicator analyses to group 388 plots into distinct communities. Red bay and swamp bay communities were significantly different in species composition. In addition, red bay was almost exclusively limited to maritime coastal forests, whereas swamp bay had a significantly larger geographical range, extending from near coastal setting inland through the fall-line sandhills. I surveyed plots from 1 to 10 years post LWD in South Carolina and Georgia. We did not find evidence of invasive species abundance increasing after LWD. Nearly all Persea in a plot are killed within the first two years of LWD, with the exception of smaller stems under 2.5 cm in diameter. After 10 years, Persea has regained much of the basal area prior to infection, however the structure of the stand is predominantly composed of small diameter stems (1 – 5 cm DBH). Seedling densities remain relatively the same throughout all recovery years. Contrary to initial fears, this study suggests that the native Persea species in the U.S. are not on the immediate verge of extinction from LWD at this time. However, it is still too early to say whether these species will fully recover from the disease.
Recommended Citation
Shearman, Timothy M., "Impacts of Laurel Wilt Disease on Native Persea of the Southeastern United States" (2016). All Dissertations. 1656.
https://open.clemson.edu/all_dissertations/1656