Posted on 06/10/2004 10:18:14 PM PDT by mdittmar
Study Finds Oversize Deer Herd, Exotic Plants Hurting Wisconsin Forest Diversity
The forests of northern Wisconsin have had significant losses of native plant species in the past 50 years, a new study concludes. The study blames an oversize deer herd and the arrival of exotic plants as key factors in the changes, which were not found on tribal forests where deer numbers are kept lower and development is closely controlled.
Scientists at the University of Wisconsin-Madison did the comparative study by returning to forest tracts mapped in the early 1950s by the late John T. Curtis, author of "The Vegetation of Wisconsin," and fellow UW botanist Grant Cottam.
The work done by the two gives Wisconsin an ecological baseline that exists in few other places in the world, according to UW officials.
The new survey of 62 carefully selected sites found less variety in plant life, which could mean there also is less habitat for insects, animals and birds.
Researchers noted that when deer feed on plants, the plants that replace them tend to be the so-called "generalists" such as ferns, sedges and grasses, as well as invasive species such as orange hawkweed, Kentucky bluegrass and hemp nettle.
Thomas Rooney, a senior scientist at the UW-Madison and one of the study's authors, said the changes can make places less favorable for tree seedlings to germinate and for some insects, birds and animals to live.
For example, removing a plant such as wild sarsaparilla takes away a valuable food source for the wood thrush and hermit thrush.
The findings by Rooney and lead researcher UW-Madison botanist Don Waller are published in the June issue of Conservation Biology.
"I think that what we have here is both good and bad news," Waller said. "The bad news is that these sites are becoming more homogeneous. The good news is that it doesn't have to be this way."
Waller, Rooney and two other researchers, Shannon Wiegmann and David Rogers, found that plant diversity was lowest where deer numbers were highest and there was little or no hunting pressure.
But parcels on tribal lands, where development is more tightly controlled and deer herds are smaller due to year-round hunting, had an increase in native species.
On the Menominee Indian reservation, deer numbers total about 10.4 deer per square mile, according to Don Reiter, fish and wildlife manager for the 360 square miles of tribal land.
The deer population is about twice as high in the surrounding deer management units, according to the state Department of Natural Resources.
Jonathan Gilbert, wildlife section leader for the Great Lakes Fish and Wildlife Commission, said that tribes are sometimes criticized for deer populations that are lower on than the surrounding lands.
"Now, in hindsight, when you look at the total ecosystem, it looks like the tribes are doing a better job of managing their land," Gilbert said.
The study found little change in the total number of species. In 1950, Curtis recorded 138 plant species at 62 sites. In 2000, the researchers traveled to the same locations and found 134 species. Of the 62 sites, 40 lost some plant species.
But the researchers found less diversity in plant life in each area.
The density of native species declined an average of 19 percent, while the exotic species rose 80 percent. In addition to wild sarsaparilla, other plants at risk are bluebeard lily, sessile bellwort and bishop's cap.
Among other findings:
On average, each site surveyed had lost nearly 20 percent of its native plants from 50 years ago.
Species diversity declined at 45 of the 62 sites surveyed.
Invasive species showed up on two-thirds of the sites resurveyed. Fifty years ago, they appeared only on one site.
Areas faring the worst are those where hunting is restricted, such as Brunet Island State Park in northwest Wisconsin. A native plant called the rosy twisted stalk had declined by 80 percent there, largely because of heavy deer browsing.
So far, much of the research has been on forests in northeastern and north central Wisconsin, and a few sites in Michigan's Upper Peninsula. Now researchers plan on moving to other areas of the state, also once surveyed by Curtis, to learn how the landscape has changed since the middle of the last century.
But parcels on tribal lands, where development is more tightly controlled and deer herds are smaller due to year-round hunting, had an increase in native species.
No,why that's amazing,who would have thunk it.
Don't they know? Specialty species always die out and the generalists win.
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