Potential host and range expansion of an exotic insect-pathogen complex: Simulating effects of sassafras mortality from laurel wilt disease invasion in the central hardwoods region

Laurel wilt disease is altering forests of the southeastern USA with widespread mortality to lauraceaous hosts, such as redbay (Persea borbonia (L.) Spreng.) and sassafras (Sassafras albidum (Nutt.) Nees). Sassafras is broadly distributed throughout the eastern USA and could serve as a pathway for laurel wilt disease spread into deciduous forests. The resulting invasion and widespread mortality of sassafras would affect these forests ecologically. In anticipation of this, we used preexisting vegetation data and the Forest Vegetation Simulator to predict future characteristics of invaded and noninvaded forests under two sassafras mortality scenarios, 33% and 99%. We calculated changes in total basal area and basal area of dominant species to assess the effects of invasion on forests of central Kentucky. We found that simulated sassafras mortality immediately resulted in significant declines to total basal area (0.87-2.32 m²/ha reductions) and also affected basal areas of selected species over time. Yellow poplar (Liriodendron tulipifera L.) and red maple (Acer rubrum L.) had the largest response to sassafras decline with long-term increases in basal area under both invasion scenarios. In contrast, the basal area of Quercus spp. as a whole only increased in the scenario with 99% sassafras mortality and only for a 15-yr period. Of the three oak species, black oak (Quercus velutina Lam.) was the only one to demonstrate significant long-term basal area increases, but again only within the 99% simulation. Our results suggest that if laurel wilt disease spreads north into deciduous forests, the resulting decline of sassafras will alter forest characteristics and affect ecological interactions, even at low levels of sassafras mortality.