Year of Award

2016

Document Type

Thesis

Degree Type

Master of Science (MS)

Other Degree Name/Area of Focus

Forest Management

Department or School/College

College of Forestry and Conservation

Committee Chair

Andrew J. Larson

Commitee Members

R. Travis Belote, John M. Goodburn

Keywords

Western larch, precommercial thinning, density management, carbon, competition, long-term studies

Publisher

University of Montana

Subject Categories

Forest Biology | Forest Management | Other Forestry and Forest Sciences

Abstract

Long-term silvicultural experiments can be used to test novel ecological hypotheses and answer contemporary management questions that were not envisioned at study initiation. We used a 54-year old western larch precommercial thinning (PCT) study in northwest Montana to examine two sets of questions: (1) how different PCT regimes affect long-term stand yield and tree growth, and (2) how PCT affects total aboveground carbon (C) storage and distribution among C pools. The study has three target densities (494 trees ha-1, 890 trees ha-1, and 1680 trees ha-1) and three numbers of entries to achieve those target densities (1, 2, and 4 entries). We included unthinned plots for comparison in our C analysis. We measured multiple tree attributes and sampled three additional aboveground C pools: understory/ mid-story vegetation, woody detritus, and forest floor material. Tree measurements were used to calculate tree- and stand-level attributes, as well as total live tree C. Carbon samples from other pools were processed in a lab. ANOVA and linear contrasts were used to test specific research questions.

Results from our yield analysis found long-term constant yield and constant volume growth over a range of densities. The primary effect of early thinning is to control whether volume and tree crown are concentrated on few large individuals or spread over a greater number of small individuals. Top height was negatively affected by higher densities. Height to diameter ratio, an attribute related to tree stability, acted to increase mortality in high density plots, decreasing yield at higher densities.

Three main conclusions follow from our examination of effects of early thinning on total aboveground C. (1) Fifty-four years after treatment total aboveground C of stands precommercially thinned to a wide range of densities is similar, due primarily to the increase in mean tree C of trees grown at lower stand densities. (2) Sixty-two years after stand replacing disturbance deadwood legacies from the pre-disturbance forest still play an important role in long-term C storage. (3) Given enough time since early thinning, there is no trade-off between managing stands to promote individual tree growth, and maximizing stand level accumulation of aboveground C.

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© Copyright 2016 Michael S. Schaedel