Appetite for trouble
Wisconsin Natural Resources Magazine, Oct 2007
Even small numbers of deer can have dramatic consequences where the land can’t support a larger herd. At a deer density of 12 to 15 animals per square mile of range, herbaceous plants like trillium, Indian cucumber, showy lady’s slipper and white fringed orchid decline. When deer densities reach 20 to 25 animals per square, species like pines, white cedar, hemlock, oaks and Canada yew can stop regenerating and small mammals like red-backed voles, an important prey species, starve out without the forest floor vegetation they need. At 25 to 35 animals per square mile of range, birds like hooded warblers decline from lack of needed ground, shrub and tree layers.
The impact of deer on relationships between tree growth and mortality in an old-growth beech-maple forest
Zachary T. Long, Thomas H. Pendergast IV, Walter P. Carson, Department of Biological Sciences, University of Pittsburgh
Forest Ecology and Management 252 (2007)
White-tailed deer have been at high levels in the northeastern forests of the United States for decades and have strongly influenced forest dynamics. In this long-term study, we found that the composition of the overstory and understory assemblages of an old-growth beech-maple forest differed significantly. We used exclosures to test the hypothesis that deer contributed to these differences by differentially influencing the relationship between growth and mortality among seedlings of the six most abundant tree species. In the absence of deer, we found that the mortality of the six species decreased with increased growth and that interspecific differences in the relationships between growth and mortality coincided with previously observed shade-tolerance rankings. In the presence of deer, mortality decreased with growth only for the browse tolerant species (American beech, black cherry, and sugar maple). Mortality did not decrease with growth for preferred browse species (oak species, ash species, and red maple), rather, this relationship was eliminated in the presence of deer. The changes in growth and mortality relationships in the presence of browsing generally corresponded to observed changes in seedling density following the removal of deer. Sugar maple, ash, black cherry, and total stem density increased in the absence of deer. Our results suggest that the relationship between survival and growth in the understory, a metric of shade tolerance, is a fairly plastic response that varies depending upon the presence and absence of herbivores. Our results indicate that deer have contributed to the differences between understory and overstory vegetation, with browse tolerant species increasing in abundance at the expense of preferred browse species.
Michigan’s Natural Communities: Rich Conifer Swamp
Michigan’s Natural Features Inventory, 2007
Long-term conservation of rich conifer swamps will require reducing deer densities across the landscape and allowing natural disturbances such as windthrow to create the complex structure that creates habitat for late-successional species.
Overabundant White-tailed Deer and the Alteration of Forested Communities
Department of Ecology and Evolution, Rutgers University-School of Environmental & Biological Sciences, 2006?
Deer can have profound effects on preferred woody and herbaceous browse species. Deer browse of woody vegetation alters the subcanopy and the shrub layer which are made up of small understory trees, young recruits for future canopy openings, and shrubs. The overbrowsing of the herbaceous level affects one level and can virtually eradicate an entire plant during one browsing episode.
Dr. Victor Reinstein Woods Nature Preserve Unit Management Plan
Town of Cheektowaga, New York, 2006
One of the major threats to the continued existence of the mature forest at Reinstein Woods is the large deer population. The town of Cheektowaga has begun a town-wide bait and shoot program to reduce the size of the population. The program is expected to take several years to achieve a significant reduction in the size of the population. Therefore, DEC plans to go ahead with establishing deer exclosures in strategic locations to encourage regeneration of desirable tree species in the forest… Two deer exclosures within the Woods give visible evidence that the deer population is impacting the forest within the Woods.
Seed dispersal by white-tailed deer: implications for long-distance dispersal, invasion, and migration of plants in eastern North America, Jonathan A. Myers, Mark Vellend, Sana Gardescu, P. L. Marks,
We investigated the potential for white-tailed deer (Odocoileus virginianus Zimm.), the dominant large herbivore in much of eastern North America, to disperse seeds via endozoochory. This is the first comprehensive study of seed dispersal by white-tailed deer, despite a vast body of research on other aspects of their ecology. More than 70 plant species germinated from deer feces collected over a 1-year period in central New York State, USA. Viable seeds included native and alien herbs, shrubs, and trees, including several invasive introduced species, from the full range of habitat types in the local flora. A mean of >30 seeds germinated per fecal pellet group, and seeds were dispersed during all months of the year. A wide variety of presumed dispersal modes were represented (endo- and exozoochory, wind, ballistic, ant, and unassisted). The majority were species with small-seeded fruits having no obvious adaptations for dispersal, underscoring the difficulty of inferring dispersal ability from diaspore morphology. Due to their broad diet, wide-ranging movements, and relatively long gut retention times, white-tailed deer have tremendous potential for effecting long-distance seed dispersal via ingestion and defecation. We conclude that white-tailed deer represent a significant and previously unappreciated vector of seed dispersal across the North American landscape, probably contributing an important long-distance component to the seed shadows of hundreds of plant species, and providing a mechanism to help explain rapid rates of plant migration.
Height of White-Flowered Trillium (Trillium Grandiflorum) as an Index of Deer Browsing Intensity
Roger C. Anderson
Feb 1, 1994
Trillium stem height was positively correlated with reproductive output by perennial herbaceous plants and negatively correlated with the percent of the herbaceous understory that is browsed. This indicates change in stem height is as indication of the general status of the herbaceous flora as influenced by deer browsing. Based on deer population densities associated with study sites supporting Trillium populations with stable stem heights and flowering plants, maintenance of deer densities of 4—6 individuals/km2 is recommended for deciduous forests in northeastern Illinois.
Impacts of White-tailed Deer On Endangered and Threatened Vascular Plants
Natural Areas Journal, 1992.
To assess the impact of white-tailed deer on flora, a review of pertinent literature and a telephone survey of professional botanists, endangered species scientists, natural area managers, and US National Park Service resource managers was undertaken. Ninety-eight species of threatened or endangered plants were reported disturbed by deer. Monocots and dicots comprised 39.8% and 56.1%, respectively, of the species disturbed. Of the disturbed species, 38.7% belonged to families Liliaceae and Orchidaceae.
The terrestrial vegetation and flora of North and South Manitou Islands, Sleeping Bear Dunes National Lakeshore
University of Michigan, 1983
The vegetation and flora of North and South Manitou Islands in northern Lake Michigan were surveyed during the summer of 1982 and the spring of 1983, the first comprehensive study of both islands. The vegetation associations were mapped and described, and a catalogue of 490 vascular plant species was compiled. A noticeable difference in forest structure and floristic composition between the islands was observed, largely due to an introduced deer herd on North Manitou. Twenty permanent plots were established on the islands to observe any future changes at selected sites. The island distributions of eight native species listed as threatened or of special concern by the State of Michigan were mapped and fragile habitats were identified.