Forest
Stewardship News Release
November
1 , 2004- For Immediate Release
Contact: Allyson
Muth , Phone: 814-863-0401 E-mail: abm173@psu.edu
The Complexities of Deer Overabundance and Forest Growth and Development
When you're
in the woods this fall, look at the habitat within the forest. What do
you notice? If what you see is a distinct browse line along the trees,
an absence of herbaceous plants and shrubs, or a dense understory of ferns,
grasses, beech, or striped maple, you may be in an area suffering from
the impacts of too many deer.
Deer overabundance is a serious problem in many parts of Pennsylvania.
White-tailed deer are a natural part of the forest ecology. Unfortunately,
a combination of historical and ecological occurrences has allowed deer
populations in the northeastern U.S. to rise to levels that result in
more than just human-centered problems, such as motorist-deer accidents,
garden destruction, or Lyme disease spread. "In the long-term, deer
have the capability of changing forest ecology, by changing the direction
of forest vegetation development," says Dr. Stephen Horsley. Such
changes could result not only in damage to the forest's ecological
integrity but also to the humans who depend on it environmentally, for
hunting, birding, recreation, and lumber.
A recently released report by the USDA Forest Service Northeastern Research
Station delves into the complexities and outcomes of too many deer on
the forests of Pennsylvania. The Winter 2004 Forest Science Review presents
results from a USDA Forest Service study on deer overabundance and its
effects on forest regeneration, species composition, songbird populations,
and wildflowers and other understory vegetation.
The report cites a study, published by Drs. Stephen Horsley, Susan Stout,
and David S. deCalesta in the journal Ecological Applications, which examined
the effects of various levels of deer populations on the forest. Fenced
160-acre study sites were built to exclude local deer populations, then
populated with deer at four specific levels: 10, 20, 38, and 64 deer per
square mile. Each study site was treated so that it contained 10% clearcut,
30% thinned, and 60% untreated forest. The scientists measured and analyzed
the vegetation and found that deer affected the abundance and density
of all plants; the horizontal and vertical structure of the forest; species
abundance of herbaceous plants, shrubs, and birds; species composition
and biodiversity of the forest understory; and resilient versus deer-preferred
foods. Translating this study onto the larger landscape means that we
see very little undergrowth left in the forest except for plants that
deer don't like. Wildflowers and the middle level of shrubs such as virburnums
and small trees, which are home to many native songbirds, are no longer
present and fewer songbirds are to be seen. There are no saplings of sugar
maple, white ash, pin cherry, or oaks.
The chosen deer densities studied represent the range that has been found
in Pennsylvania forests from pre-European settlement days in the early
to mid-1800s through the peak densities of the 1960s and 70s in the region.
During the late 1960s through the early 80s deer herds in northwest Pennsylvania,
for example, reached levels of 40 to 60 deer per square mile. The average
density of deer per forested square mile in Pennsylvania was 35 in 2001,
according to the Pennsylvania Game Commission, and in some forested areas,
deer populations remain much higher.
During the 1990s Pennsylvanians passed new initiatives allowing hunters
to reduce deer populations and their impacts. However, many forests have
already developed serious problems after 70+ years of deer overabundance.
Understories are crowded with species less preferred by deer or resilient
to their browsing pressure, such as hay-scented and New York fern, striped
maple, and beech. When understories become dominated by such species,
simple reductions in deer density may not always be sufficient to restore
healthier understory growth, diversity, and development. "We think we
know our forest. But in Pennsylvania and many other parts of the Northeast,
deer overabundance has changed our forests so much and for so long that
we truly don't know how our forests would look without too many deer,"
adds Dr. Susan Stout.
Copies of Forest Science News are available from the School of Forest
Resources, Cooperative Extension, The Pennsylvania State University. Call
1-800-235-WISE or email RNRext@psu.edu.
Excerpted from Forest Science News, USDA Forest Service Northeastern Research
Station, Winter 2004, Issue 1.
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