White-tailed deer (Odocoileus virginianus) browse damage in Ann Arbor, Michigan;
Bird Hills Nature Area, Winter 2015
Jacqueline Courteau, Ecologist, Moriah Young, University of Michigan, Independent Study Research This survey of 142 tree saplings (less than 2 meters tall) and shrubs in Bird Hills Nature Area shows that 80% have been browsed by deer, and 51% have half or more branches browsed. This level of browsing could interfere with forest regeneration and diminish the flowers and fruit available for birds, butterflies, and bees. Further monitoring would be necessary to track mortality, to reveal whether particular tree and shrub species of concern are browsed in future years, and to assess whether wildflower species are also being heavily browsed.
The deer browse figures compiled in this survey may underestimate actual browse damage in several ways. First, the survey excluded plants that were already dead or lacked live buds for identification. Many of the excluded plants showed clear signs of deer browse, which suggests that browse damage could be contributing to mortality, but estimating browse-related mortality was beyond the scope of this study. Numerous other studies suggest that browse damage over several decades may already have eliminated or greatly reduced populations of deer-preferred species (Côté et al. 2004, Rooney and Waller 2003, Ferker et al. 2014). Second, it is not possible to count how many buds are missing from a plant, so we focused on the number of branches browsed. However, some unbrowsed branches were counted even if they were quite small, while the portions of branches browsed off may have been larger than those that remained. Third, we assessed browse damage on all species, rather than on a set of species known to be preferred by deer; damage on preferred species could be even higher.
In a long-term experimental demography study, excluding ungulates reversed invader’s explosive population growth rate and restored natives
Proceedings of the National Academy of Sciences of the United States of America, vol. 111 no. 12, Mar 25, 2014
Susan Kalisz, p. 4501–4506.
In a long-term experimental demography study, excluding ungulates reversed invader’s explosive population growth rate and restored natives.
The study was long-term, over six years in a PA woodland with a deer population of 20-42 deer per km-sq (51-107 mi-sq), a population similar to some areas of Washtenaw County. There’s a lot of data and statistics in the report, and it shows that the garlic mustard population “explodes” (their “technical” term) where deer had access, but declines where deer were excluded. The ability of native plants to successfully compete with garlic mustard was dependent on the extent of deer browse. Deer never browsed on the garlic mustard, but selectively browsed the native plants.
For our natural areas to sustain the native plants that support a community of other wildlife, the PA study shows that the deer need to be managed at a level where the native flora can survive.
Washtenaw County Parks and Recreations
Status Report: Deer Population Trends and Impacts in County Parks, February 2014,
Shawn Severance, county naturalist
The deer population in Washtenaw County is elevated and increasing – The proposed DNR goal for Washtenaw County is 28 deer per square mile. Washtenaw County as a whole is currently 25% over the goal at 35 deer per square mile. The deer population in Washtenaw County has been steadily increasing over the last 15 years. Washtenaw County seems to be a magnet for deer due to a higher percentage of forested land than many of the adjacent Counties
Metroparks 2010 – 2011 Deer Management Plan Implementation Report, Meeting of Oct 11, 2011
“This year, 2010, was the first time since 1993 that (Trout Lily and) Michigan Lily were observed in blossom. Deer seem to have a special affinity for members of the lily family, and this plant is no exception. We have been anticipating the return of this species ever since the deer culls began in 1999.”