Robust Prediction of Treefall Pit and Mound Sizes from Tree Size Across 10 Forest Blowdowns in Eastern North America

Treefall pits and mounds, formed when trees are uprooted by wind, influence an exceptionally broad range of phenomena in forests, having impacts on vegetation composition, soil formation, erosion, and soil respiration, among other processes. For example, treefall pits and mounds are known to have plant species composition with more pioneer species than nearby undisturbed soil; these microsites also are wetter (pits) or drier (mounds) than undisturbed soil; and have lower rates of soil respiration. Therefore, knowledge of the extent or coverage of these microsites will improve estimates of several processes as well as vegetation composition at the stand and landscape scale. Such information would be timely, given predictions of climate-change driven increases in severe weather that is the primary agent of pit and mound formation. However, to date, there have been no attempts to define a robust relationship to predict the sizes of these microsites across multiple forest types in eastern North America. Here, we summarize field measurement of the relationship between tree size and treefall pit and mound sizes, across ten catastrophic windthrow study sites. We find that for all ten sites pooled, simple ln-ln regression explains almost 54% of the variation in sizes of treefall pits (n = 1,039) and treefall mounds (n = 962) on the basis of tree diameter. This relationship spans numerous soil types, 31 tree species, and tree sizes ranging from 5 cm to greater than 105 cm diameter. Such a relationship may be coupled with information on the severity of disturbance (for example, proportion of stems uprooted) and pre-disturbance tree size structure, to provide a basis for predicting the area covered by pit and mound microsites at the landscape scale, and thereby a basis to frame expected impacts on soil formation, carbon cycling, vegetation establishment, and other ecological, edaphic, and biogeochemical processes.