Defenders' Experts
Thinning to Promote Biodiversity
Scientists in the Pacific Northwest have been working on techniques to speed development of old-growth characteristics in second-growth forests as one way to enhance biodiversity values on landscapes that have already been heavily modified by human activities.
Economic analysis suggests that some of these techniques may ultimately allow biodiversity-oriented land managers to generate financial returns approaching those produced by intensive management for commodity production.
The federal government's Northwest Forest Plan calls for extensive use of
thinning in existing plantations to accelerate the processes that create complex
older forests. Although research has focused on young (less than 80 years)
stands on federal lands designated for management as "late successional
reserves," the findings could apply to any forest ownership and at various
scales.
Forest Service researcher Andy Carey, now retired, has focused on how stand
complexity and the presence of "decadent" elements such as snags and logs
affects biodiversity. He specifically examined the effects of various forms of
thinning on squirrels and other small mammals, birds, fungi, as well as the
interactions among those species.
Carey's research indicates that "variable density" thinning may have better
prospects for maintaining or restoring biological diversity than would either
traditional thinning or simply letting dense second-growth forests alone.
Traditional thinning leaves evenly spaced trees.
Variable density thinning allows more flexibility to retain existing snags, logs and deciduous trees, as well promoting shrubs and complex canopies. The traditional thinning goal of increasing the growth rate of retained trees would still be achieved.
In late-successional reserves on federal public lands, thinned stands would be left to develop into old forests that would be more likely to exhibit complex ecological and habitat values.
However, variable density thinning also holds out promise for improved biodiversity values on other public and private lands managed for timber production - especially when combined with longer rotations and retention of biological legacies (snags, logs, green trees) when the stand is harvested.
Computer modeling indicates that stands managed with variable-density thinning and extended rotations may provide 82 percent of the economic return produced through conventional thinning and short rotations, traditional strategies to maximize economic values.
For further information, read Thinning, Fire, and Forest Restoration: A Science-based Approach for National Forests in the Interior Northwest by Rick Brown. Released in November 2000.
In this section. . .
Many conservation biologists are looking to the broader landscape for options to help conserve forest biodiversity.
Two landscape-level plans take different management approaches: the Northwest Forest Plan and the Blue River Landscape Study.
The Northwest Forest Plan is a system of late-successional reserves that are intended to provide essential habitat for northern spotted owls and other terrestrial wildlife associated with old-growth forests.
The Blue River Landscape Study is a long-term project designed to test an alternative landscape management strategy based on historical fire regimes and other disturbance processes.
Variable density thinning allows more flexibility to retain existing snags, logs and deciduous trees, as well promoting shrubs and complex canopies.
