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Thinning may be key to forest growth
CORVALLIS, Ore. — For decades, land managers had assumed that the dense young forests that blanket much of the Pacific Northwest would grow to resemble the old-growth forests they replaced.
Associated Press Deseret News
But a new study by U.S. Geological Survey and Oregon State University researchers suggests that will not happen unless the young forests are selectively thinned to allow the remaining, uncut trees to grow under less-dense conditions.
Crowded young trees develop differently from more open-grown individuals, the scientists found. And young trees that are widely spaced will have larger crowns and diameters than closely spaced trees of the same species and age.
Dense young forests typically have more than 200 trees per acre at 50 years of age, but studies of 90-year-old growth forests revealed an average of just six to eight large trees per acre.
The researchers also contrasted the responses of plants and animals in three types of forest stands in western Oregon — young stands thinned by commercial techniques about 20 years ago, young unthinned stands and old-growth stands.
They found that:
— Thinning dense, young-growth stands increased the diversity and abundance of some lichens, particularly those that are important as forage for wildlife.
— Hardwood trees and old conifers remaining in young stands hosted diverse and abundant lichens and mosses.
— The abundance of forest songbirds was greater in thinned young stands and old-growth stands than in young unthinned stands, and the number of different species of birds was linked with the presence of hardwood trees.
— Thinned stands encouraging hardwood shrub growth had more caterpillars and other insects, which are important foods for several types of birds living in the forest understory.
"Taken together, these studies suggest that thinning may have positive results for plants and animals if the methods used protect shrubs, hardwoods, large trees and old trees," Oregon State forest scientist John Tappeiner said.
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