Assessing the stand size of bay trees (Persea spp.) after exposure to laurel wilt disease in a North Florida Preserve

Abstract

Although laurel wilt disease was first reported in the United States in 2002 from redbay trees (Persea borbonia) around Savannah, Georgia it has rapidly spread throughout the southeastern coastal plain including Georgia and Florida. In the current study, transects were used to assess the spread and impact of the disease on two native bay trees redbay (P. borbonia) and swampbay (P. palustris) from north Florida in a semi-naturalized ecological preserve. Although tree size and mortality rates have been reported previously, this study provides the first size-based static life tables for both species. While a significantly higher percent (76%) of swampbay trees exhibited signs of laurel wilt disease compared to redbay trees (62%); redbay had more of its canopy damaged by the disease (41% vs. 32% for redbay vs. swampbay respectively); this resulted in a significantly smaller stem diameter for P. borbonia compared to swampbay, both species are experiencing significant declines due to the disease. Both species exhibited a Type III survivorship curve in which the vast majority of individuals were in the smallest size class (average stem diameter was only 2.5 and 3.6 cm for redbay and swampbay respectively). Although traditionally, population age (or size) structure that is heavily biased toward younger or smaller size classes suggests that the population is likely to expand in the future, for these bay trees high mortality rate due to beetle/fungal infestation of larger size classes is responsible for this trend; the smallest size classes are largely free from beetle infestation and laurel wilt disease because the stem diameter is likely insufficient to support beetle development. Results from this study suggest that swampbay is also highly susceptible to laurel wilt disease and its populations are likely to exhibit a similar (albeit slower) decline in Florida’s wetland and mesic ecosystems.