Forest Restoration Using Variable Density Thinning: Lessons from Douglas-Fir Stands in Western Oregon

Klaus Puettmann,Erich Dodson,Julia Burton,Adrian Ares

doi:10.3390/f7120310

Klaus Puettmann, Erich Dodson + Show 2 more

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https://doi.org/10.3390/f7120310

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Journal: Forests	Publication Date: Dec 7, 2016
Citations: 35	License type: CC BY 4.0

Affiliation: Oregon State University, Utah State University

Abstract

A large research effort was initiated in the 1990s in western United States and Canada to investigate how the development of old-growth structures can be accelerated in young even-aged stands that regenerated following clearcut harvests, while also providing income and ecosystem services. Large-scale experiments were established to compare effects of thinning arrangements (e.g., spatial variability) and residual densities (including leave islands and gaps of various sizes). Treatment effects were context dependent, varying with initial conditions and spatial and temporal scales of measurement. The general trends were highly predictable, but most responses were spatially variable. Thus, accounting for initial conditions at neighborhood scales appears to be critical for efficient restoration. Different components of stand structure and composition responded uniquely to restoration thinnings. Achieving a wide range of structures and composition therefore requires the full suite of silvicultural treatments, from leave islands to variable density thinnings and creation of large gaps. Trade-offs among ecosystem services occurred as result of these contrasting responses, suggesting that foresters set priorities where and when different vegetation structures are most desirable within a stand or landscape. Finally, the results suggested that foresters should develop restoration approaches that include multiple treatments.

Highlights

At the time of European settlement, vast areas in the western portion of the Pacific Northwest in the United States were covered with old-growth conifer forests, primarily dominated bylong-livedDouglas-fir (Pseudotsuga menziesii (Mirb.)) and western hemlock (Tsuga heterophylla (Raf.)) capable of attaining massive sizes [1]
Douglas-fir and western hemlock often naturally regenerated after early harvests, as planting and seeding was uncommon
The small-scale spatial variability in pre-treatment vegetation and environmental conditions is likely to result in highly variable outcomes, even if restoration treatments are applied homogenously

Summary

Introduction

At the time of European settlement, vast areas in the western portion of the Pacific Northwest in the United States were covered with old-growth conifer forests, primarily dominated bylong-lived. Douglas-fir (Pseudotsuga menziesii (Mirb.)) and western hemlock (Tsuga heterophylla (Raf.)) capable of attaining massive sizes [1]. Native Americans living in the region used wood for various purposes, such as building harpoons, mats, and baskets, but did not harvest and manufacture products from trees on a large scale. They managed forests by setting fires, e.g., to encourage food crops such as huckleberry or camas, or to improve traveling and hunting opportunities [2].

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