Increasing Aspen Production through Mechanical Strip-Thinning (December 1, 1992-May 31, 1993): Monitoring Report

Abstract

This project has five primary research tasks related to the determination of growth and yield of aspen in response to mechanical strip-thinning; analysis of disease incidence in thinned and unthinned stands and determination of the costs and economic feasibility of mechanical stripthinning of aspen. Studies of growth through the 1992 growing season on recently-thinned aspen stands have shown an average growth increase due to thinning of 15 percent over unthinned stands. Statistical analysis shows a strong correlation between initial tree size and the magnitude of the growth response to thinning. Growth of the largest trees in thinned areas is 34 percent faster than unthinned areas of the stands. Evaluation of site characteristics continues with textural analyses completed on the majority of soil samples collected to date. Indices of stand density and initial tree diameter distribution are being developed for the fourteen stands in the experimental network. Analysis of previously-thinned stands on the Chippewa National Forest shows that thinned stands have more than twice the merchantable volume than an unthinned stand at this time. This indicates that the ultimate goal to reduce harvest rotations of aspen by ten years is likely attainable on some sites in Minnesota. Summary tables describing disease incidence and severity for all sites have been prepared. Differences between thinned and unthinned stands in mechanical injury is evident at some sites. Variation in disease incidence and severity is apparent between sites. Economic analyses have continued with additional information collected on thinning costs and operational feasibility. Two sites evaluated in the spring showed extremes of the previously-established range of thinning costs. Costs per acre were $8.50 at one site and $20 per acre at another. This is due to differences in terrain and stand composition.