Understanding and emulating natural processes in management is one approach to ecosystem management. Emulating wind disturbances has focused on residual live tree stem (e.g., diameter distribution) and canopy cover (e.g., gap density and size) and less on residual microtopography. Mounds created by tree tipping, in particular, expose mineral soil, release nutrients slowly, provide refugia from deer, and present a unique microsite for tree regeneration. We compared the mound features in old-growth, unmanaged forests that have and have not experienced moderate-severity wind disturbances 10-12 years ago. We hypothesized that where recent blowdown disturbance has occurred, there will be a greater proportion of recently formed mounds, a greater density of mounds, and more mineral soil exposure than in areas undisturbed by recent blowdown. We also expected a high abundance of all sapling species, especially light-seeded tree species, such as Betula alleghaniensis, on mounds in recently disturbed areas. We tested our hypotheses at four northern hardwood forests of Wisconsin, USA. At each site, we used a split-plot design, split by disturbed and undisturbed areas of recent blowdown. We surveyed mound density, age, and exposed mineral soil and sapling species, density, and mounding status (on/off).
Results/Conclusions
We found similar mound density in recently disturbed (12.8 mounds/ha) and undisturbed (11.6 mounds/ha) areas. Recent mounds (3.2 mounds/ha) and exposed mineral soil (7.5%) were more prevalent in recently disturbed than undisturbed areas (<1 mound/ha and 1.6%, respectively). The relative density of saplings of any size displayed a possible interaction between disturbance and mounding (df=6, F=4.7, p=0.07). Sapling density was greater on mounds in recently disturbed areas than off mounds or on mounds in undisturbed areas, providing marginal support for our hypothesis. For small (<2.54 cm diameter at breast height [DBH]) light-seeded species, there was a possible interaction between disturbance and mounding (df=6, F=16.0, p=0.07), with greater sapling density on mounds in recently disturbed areas than mounds in undisturbed areas, partially supporting our hypotheses as well. As predicted, the relative density of large (>2.54 DBH) light-seeded species was 1.3 times greater on mounds than non-mound areas (df=6, F=6.58, p=0.04). Overall, mounding and recent blowdown disturbance influenced tree regeneration density and composition. The results highlight the role that mounding could potentially play in managing forests for tree diversity and other ecosystem services.