The biggest threat for Virginia forests, a new study suggests, may be people.

A recent report from the Virginia Department of Forestry warns that the state could soon reach the point where the consumption of wood, paper and other forest products exceeds the rate at which they can be produced from available land.

It’s not that the state is running out of forests, according to the “Virginia Forest Land Assessment” report, but rather that more people are moving into them, making woodlands unavailable for other uses — even as the public demands more from forests, both in terms of products, recreation and other services.

While forests expanded in the state from 1940 to 1976, they have remained fairly steady since then, at about 15.4 million acres. But not all that land is available for harvest. About 3.9 million acres are on steep slopes, small plots or arranged in such a way — such as in long, narrow strips — that harvest is not practical, according to the report.

Much of that may not be available because of the continued development of woodlands. As people move into forests, it reduces the size of woodlands and often increases land use conflicts among owners, as well as resistance to timbering.

“At some level of population density, forests which can be harvested and managed will essentially disappear,” the report said.

When foresters compared population densities to forest management throughout the state, they found that the probability of sustainable management was about zero when the number of people per square mile reached 150.

There was a 25 percent chance of management at 70 people per square mile; a 50 percent chance at 45 people per square mile; and a 75 percent chance at 20 people per square mile.

When those figures were applied statewide, another 3.1 million acres — or 20 percent of all forest land in the state — was considered unsuitable for forest management because of population pressure, according to the study.

So while Virginia has 15.4 million acres of forest land, only about 8.5 million acres, or 55 percent, is likely to remain available for timber management when areas unsuitable for harvest are subtracted from the total.

As a result, the report said, current rates of timber harvest in the state “meet or exceed” the current rate of growth on land available to management.

The report cautions that some harvests will continue to come from lands that have been classified as too populated to be used, or that the report deemed unsuitable for other reasons. And it said the state should have adequate timber land well into the 21st century.

But the report said that if the state wants a sustainable forest industry in the long term — an industry that generated an estimated $9.7 billion in economic activity in Virginia in 1995 — it will have to deal with critical issues such as land-use policy, changes in regulations and ordinances, changing citizen demand for wood products and controlling fragmentation.

“Of primary concern is the fact that rapid population growth increases demands on forest resources even as it decreases the amount and availability of forest land,” the report said. “There are obvious needs both to conserve forest land and to improve its productivity.”