Monitoring Deer Impacts on Natural Vegetation in Ann Arbor:
A Pilot Study of Red Oak Seedlings as Experimental Indicators of Deer Browse Intensity
Across 10 city parks
November 2015 – October 2016
Jacqueline Courteau, Ph.D.
Consulting Biologist/Ecologist, NatureWrite LLC
October 17, 2016
This pilot experimental study, in which red oak seedlings were planted and monitored in 10 city parks (and in a separate study at the Arboretum), found that deer are browsing 20–90% of tree seedlings, a level that exceeds the 15% recommended in existing scientific literature as allowing for sustainable tree regeneration (Blossey 2014). Overall, deer alone were responsible for 76% of the browse-damaged seedlings, with an additional 11% browsed by both deer and small mammals.
A total of 9% of seedlings were browsed by small mammals only; including seedlings also browsed by deer, 20% of seedlings showed evidence ofsmall mammal browse.
U-M biologists support Ann Arbor deer cull
Michigan News, Jan 14, 2016
A University of Michigan evolutionary biologist says he and many of his U-M colleagues support the city of Ann Arbor’s plans to kill up to 100 deer this winter, calling the cull “a positive step toward ecological sustainability.”
U-M botanists have long noted declines in native plants that deer favor, Dick said. In a 2015 study, an ecological team surveyed browsing impacts in Ann Arbor’s Bird Hills Nature Area and found browsing damage in 80 percent of the tree saplings.
Sustainable Management of White-Tailed Deer and White-Cedar
Laura S. Kenefic, Jean-Claude Ruel and Jean-Pierre Tremblay
The Wildlife Society, Oct 5, 2015
Using recent and historical regeneration data from the Forest Service’s permanent sample plots, Larouche and her colleagues compared the dynamics of white-cedar to those of companion species over a 40-year period and found that white-cedar seedlings have not progressed to larger-size classes over time, while seedlings of other species have grown into sapling and merchantable-size classes (Larouche et al. 2010). Furthermore, density of white-cedar has declined in the study area since the 1960s, with close to 90 percent of sampled white-cedar seedlings and large saplings having evidence of deer browsing in 2005.
Deer impacts on vegetation and communities in the Leonard Preserve, Manchester, MI
Jacqueline Courteau, Ph.D., Sept 2015
Presence of deer is correlated with significant reductions in plant species composition, abundance and flowering, with the potential to reduce populations of spring and fall wildflowers in both forests and grasslands, and to reduce oak recolonization in old fields. 13 out of 15 indicator species in forest and grassland plots were both more abundant and more likely to flower/fruit in areas protected from deer. Although species composition and abundance data alone do not demonstrate that deer has caused the declines, the combination of data on indicator species (including clear signs of deer browse damage) strengthens the case. Effects ripple to communities and tropic levels beyond plant populations, however, because the affected species provide key resources for a range of insect, small mammal, and bird species.
Many Native Connecticut Plants in Danger, Report Warns
Hartford Courant, March 26, 2015
The report also warns that, “For the first time in 200 years, every state in New England is losing forest,” a result of human activities such as development, attacks by invasive insects, deer over-population, and the impact of climate change. .Elizabeth Farnsworth, the society’s senior research ecologist and the author of the report, said Connecticut’s and New England’s massive deer population is a major contributor to the loss of forest because deer browse on young seedlings.
Special Issue: Deer eating the future of Pennsylvania’s Forests!,
U Penn., no date
Deer population levels, when the earliest European settlers arrived, have been estimated at 9-11 deer per forested square mile. Today levels of 30-80 deer per forested square mile are not unusual and in some urban/suburban sites they are even higher.
It’s rare plants versus deer in the College Woods
William & Mary News, Jan 15, 2015
What was once lush is now sparse. “This isn’t good for the forest, but it isn’t good for the deer either,” said Dalgleish. The problem is not simply that the deer are eating too many plants, but that the plants are growing back smaller and smaller each year. The deer are eating the plants so quickly that they are unable to store enough regenerative material to grow back to their original height the next year.
Deer account for almost half of long-term forest change, study finds
University of Wisconsin-Madison News, January 2, 2015
A study released this week has linked at least 40 percent of species changes in the forests of northern Wisconsin and Michigan over the past 60 years to the eating habits of white-tailed deer.
Long-Term Regional Shifts in Plant Community Composition Are Largely Explained by Local Deer Impact Experiments
PlosOne, Dec 31, 2014
The fact that herbivores and predators exert top-down effects to alter community composition and dynamics at lower trophic levels is no longer controversial, yet we still lack evidence of the full nature, extent, and longer-term effects of these impacts. Here, we use results from a set of replicated experiments on the local impacts of white-tailed deer to evaluate the extent to which such impacts could account for half-century shifts in forest plant communities across the upper Midwest, USA. We measured species’ responses to deer at four sites using 10–20 year-old deer exclosures. Among common species, eight were more abundant outside the exclosures, seven were commoner inside, and 16 had similar abundances in- and outside. Deer herbivory greatly increased the abundance of ferns and graminoids and doubled the abundance of exotic plants. In contrast, deer greatly reduced tree regeneration, shrub cover (100–200 fold in two species), plant height, plant reproduction, and the abundance of forbs. None of 36 focal species increased in reproduction or grew taller in the presence of deer, contrary to expectations. We compared these results to data on 50-year regional shifts in species abundances across 62 sites. The effects of herbivory by white-tailed deer accurately account for many of the long-term regional shifts observed in species’ abundances (R2 = 0.41). These results support the conjecture that deer impacts have driven many of the regional shifts in forest understory cover and composition observed in recent decades.
Deer density and plant palatability predict shrub cover, richness, diversity and aboriginal food value in a North American archipelago,
Diversity and Distribution, Sept 2014
We provide comparative examples of endangered plant communities to demonstrate that, contrary to the intermediate disturbance hypothesis, any positive effect of deer on plant diversity on islands in the Pacific north-west of North America occurs at densities < 0.08 ha−1, if at all. This detailed example of trophic downgrading highlights the need and provides the methods to identify herbivore densities compatible with the persistence of all native species in conserved landscapes.