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CORVALLIS - Black-tailed deer, once numerous throughout the woods of western Oregon, are suffering a population decline, scientists reported at a conference this week at Oregon State University.

The event attracted about 300 wildlife and forest scientists, managers, family forest owners and hunters to explore relationships between deer and elk populations and forest practices in western Oregon.

Habitat change seems to be a main factor in the population decline, although there may be others, such as an invasive louse that spreads rapidly through deer herds.

The sag in population shows up in declining estimates of the deer population and in the lower numbers of deer harvested by hunters in recent years, said presenter DeWaine Jackson of the Oregon Department of Fish and Wildlife. The elk population has increased in recent years, but there are warning indicators that their numbers may also decline in the future.

According to presenter John Cook, a wildlife biologist with the National Council for Air and Stream Improvement, animals that don't get enough of the right kind of food in the summer and fall may not put on enough fat to carry them through the winter in good health. Undernourished females tend to have fewer young. And because the underweight mothers don't have as much milk as the healthy ones, their young also tend to be underweight, making them less likely to survive and thrive.

"We're finding that nutrition from late spring through early autumn is more important than we thought," Cook said.

While disease also has played a role in declining deer populations, the health of big game seems to be closely related to forest management, said Cook. A forest in its early successional period, the first 10 or 15 years, provides the best forage for big game. Both deer and elk prefer the deciduous shrubs and soft-stemmed plants that come in after a forest fire or clearcut. Once the forest canopy begins to close, these plants lose out to less palatable and less nutritious evergreen shrubs and ferns.

"If we want large, productive populations of deer and elk," said Cook, "scientific evidence suggests that there must be a reasonable amount of early-successional vegetation."

Good quality big-game habitat has declined significantly in recent decades, said Hal Salwasser, dean of the OSU College of Forestry. The abundance of early-successional forests that existed during the 1960s and 1970s is either maturing forest now, or it's being managed as plantation forestland, with aggressive weed control to promote fast growth of the trees.

"Federal policy has created mostly late-successional forests on federal lands for the sake of conserving old-growth wildlife," said Salwasser, a wildlife biologist. "However, forests support different species of wildlife during their different successional stages."

The species that prefer older forest are different from the ones that prefer younger forest - not only big game but other mammals and birds, Salwasser said.

"If we want the full range of forest-dwelling wildlife across our landscape, then, as a society, we need to maintain forests at their full range of successional stages," he said.

There is evidence that deer forage may be improved through strategic weed control in forest plantations, according to presenter Liz Cole, a forest ecologist with OSU's Department of Forest Science. In some of the experiments Cole described, the plants that came in after spraying may be better big-game forage than those that were growing on unsprayed sites.

In addition, an exotic louse recently introduced into the Pacific Northwest may be contributing to a decline in the general health of the deer population, said presenter Bruce Coblentz, an OSU wildlife biologist. The louse, first reported in Washington in 1995, is thought to be responsible for the hair loss observed among black-tailed deer in the past few years. Itching from the louse makes the deer bite and chew at the affected patches until their hair falls out.

Conference sponsors were the Oregon Forest Resources Institute, Oregon State University, Oregon Department of Fish and Wildlife, Oregon Forest Industries Council, and Oregon Department of Forestry.

Salwasser praised the recent initiative by the Oregon Fish and Wildlife Commission to create a comprehensive wildlife management plan with the involvement of scientists, forest and wildlife managers, hunter and other conservation interests, and the public.