Impacts due to ungulate herbivores such as moose and white-tailed deer have been of
interest to researchers and resource managers for years. Recent studies have begun to
suggest the presence of alternative stable states in these systems where the existence of
hysteresis could result in significant changes to the understory community that would be
costly and time consuming to undo. However, before such assertions can be made, the
presence of different states needs to be established. Our study investigated changes to the
understory community and nutrient dynamics of twelve paired moose and white-tailed
deer exclosure and control plots located along a 95-mile section of the Lake Superior
North Shore Highlands. Exclosure ages ranged from 11 to 24 years old. During the
summer of 2010, we measured understory and shrub species percent cover, sapling
densities, litter depth, and bulk soil composition inside and outside of exclosures at each
site. Nitrogen availability was also measured at three sites using resin bags. Browsing significantly affected understory vegetation at all sites except one, as well as ammonium
(NH4) availability and percent of nitrogen and carbon in the mineral soil. The directions
of these effects varied by site and seemed to be related to differences in canopy
composition, age of exclosure, and relative ungulate population size. Future studies
should monitor long-term changes through time, as some trends may be important early
on in forest recovery while others do not appear until years later. Although our study
design was not able to detect evidence of hysteresis or affirm the presence of alternative
stable states, we believe it does suggest evidence of instability and non-linear ecosystem impacts of ungulate herbivory.
University of Minnesota M.S. thesis. December 2012. Major: Integrated biosciences. Advisor: George Host. 1 computer file (PDF); v, 63 pages.
McGarry, Elizabeth Anne.
Effects of herbivores on ground flora and nutrient dynamics along Lake Superior's North Shore Highlands.
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