Growing Deer Population Hurts Survival Of Forests
NPR, June 15, 2011
The deer side of the fence has a carpet of grass, a shrubby looking thing, and some large trees – things that are either too big for deer to eat, or are among the very few plants they don’t like to eat. Inside it is practically a jungle. Dozens of different almost exotic looking plants are tumbling over one another. Many of them are young trees.
You have the old trees. And when the old trees go, there is something here [in the enclosure] to take its place. Out there, I don’t see anything out there that’s a small tree.
One of the surprising things they’ve found with this experiment is that deer allow invasive species to flourish. And with fewer native plants, there are fewer birds who depend on them for nests and food. There are fewer mice and fewer chipmunks here when they have to compete with deer.
Hardwood forests not regenerating as deer eat maple saplings, Michigan study shows
Science Daily, May 10, 2011
In a sweeping study of a huge swath of Michigan’s Upper Peninsula, researchers documented that in many places, the sugar maple saplings that should be thriving following harvesting are instead ending up as a deer buffet. This means the hardwood forests are not regenerating.
Legacy of top-down herbivore pressure ricochets back up multiple trophic levels in forest canopies over 30 years, Ecosphere, Jan 2011Removal of top-down control on herbivores can result in a trophic cascade where herbivore pressure on plants results in changes in plant communities. These altered plant communities are hypothesized to exert bottom-up control on subsequent herbivory via changes in plant quality or productivity. But it remains untested whether top-down perturbation causes long term changes in plants that ricochet back up the new food chain that depends on them. In a large-scale, 30-yr controlled field experiment, we show that 10 yr of top-down control of an ungulate herbivore (white-tailed deer, Odocoileus virginianus) created contrasting forest tree communities exerting bottom-up effects that ricochet back up 3 trophic levels 20–30 yr later. Higher ungulate densities during stand initiation caused significant reductions in tree species diversity, canopy foliage density, canopy insect density, and bird density in young (ca. 30 yr old) forests. Because recruitment of trees from seedlings to the canopy occurs over a relatively brief period (ca. 10 yr), with membership in the canopy lasting an order of magnitude longer, our results show that even short-term perturbations in ungulate density may cause centuries-long disruptions to forest ecosystem structure and function. In documenting this five-step trophic ricochet, we unite key concepts of trophic theory with the extensive literature on effects of ungulate overabundance. As predators decline and ungulate herbivores increase worldwide, similar impacts may result that persist long after herbivore density becomes effectively managed.
Deer Damage After Foliage Falls
Fairfield County, 2010
Dr. Georgina Scholl, Vice Chairman of the Alliance, stated “Residents have forgotten that it is not normal to look through the forest and see the rise and fall of our topography hundreds of feet out. The shrubs and saplings that once comprised the leafy understory used to block your view. Today, such lower areas look more like manicured parklands”.
With each deer consuming approximately 10 pounds of vegetation each day, the forest cannot regenerate its vegetation fast enough to support 60+ deer per square mile.
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.
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.
A demographic study of deer browsing impacts on Trillium grandiflorum
Plant Ecology, May 2003
Thomas P. Rooney and Kevin Gross
A moderate drought during the study could account for the negative population growth rate, but deer browsing accelerates the rate of decline. Population growth is most sensitive to the proportion of plants remaining in the nonflowering stage, and deer browsing reduces this proportion. Browsing damage was relatively low in this study (5.4% of stems in 1998, 11.5% in 1999) compared to another study of browsing impacts on T. grandiflorum, indicating deer could have far more severe demographic consequences in populations subject to higher levels of browsing.
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.