Mounds facilitate regeneration of light-seeded and browse-sensitive tree species after moderate-severity wind disturbance
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Forest Ecology and Management
Using natural disturbance as a guide to management is an approach to develop resilience, maintain or restore natural processes, and sustain ecosystem goods and service. Here, we compare features of mounds resulting from tree uprooting, tree structure and composition, and browsing in recent 10–12-year-old moderate-severity wind disturbance events and reference stands in old hemlock– (Tsuga canadensis–) hardwood forests in Wisconsin, USA. Compared to reference stands, recent, partial blowdown stands had reduced overstory tree density and canopy heights, and more large gaps, coarse woody debris, exposed mineral soil, and newly-created mounds. Regeneration of light-seeded species was greater in blowdown stands relative to reference stands. We found an association between old mounds and overstory eastern hemlock and yellow birch, indicating mounds provide a long-term competitive advantage for these light-seeded species relative to pits and undisturbed areas. Notably, we found that the distance to the canopy was shortened by 30% for trees regenerating on young mounds in blowdown stands. In addition, light-seeded species, such as yellow birch, grew above browse height (2 m) in 10+ years on young mounds. In contrast, on flat and pit microsites, saplings were short (< 2 m) and more likely browsed. Maintaining and/or protecting naturally created mounds may facilitate regeneration of light-seeded, browse-sensitive species in mixedwood forests that evolved under infrequent, moderate-severity wind storms. Therefore, reserving a subset of uprooted trees from salvage operations could provide suitable substrate for germination and long-term development advantages, especially for light-seeded and browse-sensitive species and stands managed for high conservation values.
KeywordsNorthern hardwoods Tip-up mounds Microtopography Natural disturbance Ecological forestry Browse refugia Tree-throw Uprooted trees Canopy gaps
Kern, Christel C.; Schwarzmann, John; Kabrick, John; Gerndt, Kathryn; Boyden, Suzanne; Stanovick, John S. 2019. Mounds facilitate regeneration of light-seeded and browse-sensitive tree species after moderate-severity wind disturbance. Forest Ecology and Management. 437: 139-147. https://doi.org/10.1016/j.foreco.2018.12.040.