A long-term deer-forest study intends to fill in gaps in understanding habitat health

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In the science of wildlife management, habitat is almost everything.

To learn how the current cottontail rabbit population cycle will impact foxes, coyotes and avian predators, evaluate rabbit habitat.

To know the optimal density of a particular migrating songbird, study the songbird's habitat.

To understand the overall health of wildlife, determine the overall health of the habitat animals need to survive.

The biggest consumer of vegetation in the forest eats 10 to 12 pounds of the habitat used by every other animal every day, and it doubles its population every two years. The white-tailed deer has a unique and dominant position in the health of forest ecosystems. Since 2000, the state Game Commission has intentionally reduced deer populations, attempting to normalize the sex ratio and stabilize deer numbers in parity with habitat.

But ecologists know that deer aren't the only variable impacting woodlands. Invasive plants, insect outbreaks, soil acidity and tree diseases are a few of the issues giving headaches to Pennsylvania forest managers.

In a long-term study starting this year, the Game Commission and its partners are trying to fine-tune analyses of deer-forest impacts including forest regeneration and evaluation methods. The collaborative program includes the state Department of Conservation and Natural Resources, Pennsylvania State University and the U.S. Geological Survey's Pennsylvania Cooperative Fish and Wildlife Research Unit.

The study area is limited to several tracts of forest land in central and northcentral Pennsylvania -- two representing typical northern hardwood forests, two of an oak-hickory forest type. Deer will be managed differently in each area by manipulating allocations of Deer Management Assistance Program permits. Researchers will analyze the impacts of various deer densities on habitat as compared with other factors.

Chris Rosenberry, supervisor of the Game Commission's deer and elk section, said hunters will perform an important function.

"We're relying on the survey work of hunters so we can fully evaluate the harvest and effects of the deer population on their hunting experience," he said. "Without their cooperation, that part of the study will disappear."

Deer aren't the only thing negatively impacting forest growth, said Rosenberry, but assessments based on deer impacts are "the most important habitat measure used in deer-management recommendations." Mostly, he said, that's because the hunter deer harvest is easier to regulate than other factors. In this unique study, hunters will establish deer control groups in designated areas while evaluation methods and other factors impacting forests are studied.

Fieldwork began in January with the capture and radio-collaring of deer in study areas in Rothrock, Bald Eagle and Susquehannock state forests. From May through August, technicians collected vegetation data on 200 permanent plots, which will be revisited every other year. In 2014, additional monitoring will occur in areas with planned timber harvests. After five years, said Rosenberry, researchers will decide whether to recommend that the study continue.

Among the study's objectives:

• Determine whether deer impact levels accurately reflect the effects of deer browsing on habitat, and identify ways to improve monitoring.

• Evaluate the effectiveness of DMAP in increasing the antlerless harvest in a specific area.

• Evaluate the effectiveness of DCNR's vegetation impact protocol to detect changes in habitat relative to the local deer population.

• Monitor the ways that hunters respond to changes in deer abundance.

Critics of the deer management plan have long argued that whitetails are only one of many things impacting forest growth. Why, they've asked, should their numbers be so radically reduced before other variables are evaluated?

Penn State deer expert Duane Diefenbach, a participant in the study, said some of that research was done before the deer plan was implemented. Deer densities needed to be under control, he said, before other factors could be properly analyzed.

"I see this as a continuation of what we've been doing for the past 15 years," he said. "It started in 2000 with [a] fawn study and led to doe harvest rates and other studies the agency used to make decisions on deer management. Now it's come down to deer numbers are reduced and we have more bucks. We have a real good handle on what the deer are doing, but one of the key objectives of the deer management plan has been to have the right habitat to support deer."

Despite deer reductions, forests in some areas are still not regenerating at necessary levels, and in other places deer still have an unsustainable impact on habitat used by every creature in the woods.

"We're at a good point now to ask two questions: a) is it because of some other factor, or b) did we not reduce numbers enough?" Diefenbach said. "We don't want to make recommendations to reduce deer numbers if that's not the issue. This study will help the DCNR to improve deer management on its lands and help the Game Commission to evaluate its metrics."

Hunters who get DMAP permits in the study areas are automatically registered to participate in the study. Rosenberry said the registration of hunters who hunt only antlered deer in the study areas, or hunt there with doe tags, will help to make the study successful.


For details about the deer-forest study and hunter registration: ecosystems.psu.edu/research/projects/deer. First Published October 19, 2013 8:00 PM


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