Structural, compositional, and functional responses to tornado and salvage logging disturbance in southern New England hemlock-hardwood forests
The frequency and severity of wind storms, such as hurricanes and tornados, are expected to increase in northeastern North America under climate change. As such, salvage logging is likely to become a more frequently-used post-disturbance management strategy; however, there is concern that the compound disturbance of wind followed by salvage logging could generate negative impacts on species composition, forest structure, and ecological resilience. These impacts are variable and uncertain, posing an opportunity for further research that considers differences in forest recovery following stand-replacing wind alone versus stand-replacing wind and salvage logging. We evaluated the short-term impacts of these singular (tornado) and interactive disturbance events (tornado + salvage logging) on the structure, composition, and function of a mature hemlock-hardwood forest in south-central Massachusetts. Specifically, we were interested in quantifying the impacts of salvage logging practices on forest recovery and resilience. Our analyses consider salvage logging impacts on forest overstory in addition to the regeneration layer (defined here as tree seedlings and saplings that make up the forest understory). We found that (i) delayed overstory mortality was highest on tornado-damaged sites, contributing additional material to dead wood pools, while salvaged sites lacked much of this material and associated structural legacies; (ii) tree regeneration layer diversity, as measured by Shannon's Index, was higher in the tornado-damaged sites than salvaged sites, but levels of sapling (>=1.4 m in height and <12.7 cm in dbh) density and richness were the same; and (iii) regeneration present on tornado-damaged sites was more functionally similar to that present on undisturbed control sites than to that on salvaged sites. Our results indicate that the compound disturbance created by salvage logging may have initially homogenized regeneration composition and pushed these areas toward disturbance-adapted species (e.g., Acer rubrum and Betula lenta) and traits (e.g., transitory on-site reproductive strategies). This shift in composition may have also been influenced by the removal of dead material and structural legacies at these sites. However, the high levels of regeneration density and richness found on both tornado-damaged and salvage-logged sites suggests that rapid forest recovery is occurring via multiple mechanisms of regeneration, such as vegetative reproduction, advance regeneration, and new seedlings. These findings highlight how post-disturbance management actions affect forest resilience and development after severe wind disturbances, and suggest that future salvage logging operations more explicitly integrate retention of structural legacies and protection of advance regeneration to enhance forest recovery.