BIRKENFELD, Ore. — Eve Lonnquist’s family has owned a forest in the mountains of northwest Oregon since her grandmother bought the land in 1919. Her 95-year-old father still lives on the 157-acre property. And she and her wife often drive up from their home just outside Portland.

But lately, Ms. Lonnquist, 59 and recently retired, has been thinking about the future of her family’s land. Like many small-forest owners, they draw some income from logging and would like to keep doing so. But they would also like to see the forest, with its stands of Douglas fir, alder and cherry, protected from clear-cutting or being sold off to developers.

“For us, the property is our family’s history,” she said.

More than half of the 751 million acres of forestland in the United States are privately owned, most by people like Ms. Lonnquist, with holdings of 1,000 acres or less. These family forests, environmental groups argue, represent a large, untapped resource for combating the effects of climate change.