Term of Award

Summer 2010

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (open access)

Department

Department of Biology

Committee Chair

Lissa M. Leege

Committee Member 1

Risa A. Cohen

Committee Member 2

John B. Pascarella

Abstract

Laurel wilt disease (LWD), a fungal disease vectored by the non-native redbay ambrosia beetle (Xyleborus glabratus), has caused mortality of redbay (Persea borbonia) in the Coastal Plain of Georgia, USA, since 2003. This disease has spread 30-100 km/year and little research has evaluated its impacts on redbay population structure and forest communities. Healthy and infested populations of redbay and their associated communities were compared in five sites infested with LWD and three un-infested sites in five counties in Georgia. Tree, shrub, and herb layers were sampled separately to determine redbay population structure and community composition and structure. Only 8% of redbay trees >3 cm diameter at breast height (DBH) were alive in infested sites, compared to 80% in control sites. Live redbay trees had 2 times greater average DBH in control sites. Dead tree stems had almost 3 times more stump sprouts per tree in infested sites. Impacts from LWD were found in redbay <1.00 cm diameter at ground height. Photosynthetically active radiation (PAR) was 4.8 times greater at infested sites due to loss of redbay canopy. Shrubs in control sites were taller with larger crowns than those in infested sites relative to stem diameter due to differences in light levels. Redbay trees had the greatest mean importance value (IV) at control sites compared to the 8th mean IV at infested sites for live stems. Redbay had the greatest mean IV in infested sites when dead stems were included. Two co-dominant species to redbay, sweetbay (Magnolia virginiana) and loblolly bay (Gordonia lasianthus), ranked 1st and 2nd in mean IV at infested sites but 2nd and 3rd in mean IV at control sites and may be increasing in importance. Increases in herbaceous pioneer species were found in infested sites. This study shows that LWD has impacted redbay populations and caused changes in associated forest communities in Georgia in 2-4 years post-infestation. Future research may show further shifts in population and community structure and consequent changes to ecosystem processes. Redbay populations may even be at risk of threatened or endangered status if this disease continues to spread throughout redbay's range.

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