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Doctor of Philosophy (PhD)
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The above-ground responses of precommercially thinned (PCT) softwood stands have been well studied in comparison with the below-ground responses. The main objectives of this project were to compare root characteristics, and butt and root decay of red spruce and balsam fir in PCT and unthinned (UT) spruce-fir stands to provide information on windfirmness and decay condition of precommercially thinned stands.
Twenty-four 1 m2 forest floor plots (all woody roots > 2.0 mm in diameter) in addition to 80 crop tree root systems (roots > 1.0 cm in diameter) were excavated by hand in 30-year-old spruce-fir stands. Half of the plots and trees were located in the stands that were PCT 18 years ago, and half of them were located in untreated stands. There was no difference in woody root density between PCT and UT stands. The average total root biomass and length was 1.2 kg/m and 65.57 m/m , respectively. For crop tree root systems, balsam fir had more root biomass and length in PCT than in UT stands. However, red spruce did not show this. Red spruce had a larger proportion of large roots and a smaller proportion of small roots than did balsam fir. Balsam fir had more deep roots than red spruce. A strong relationship was found between diameter at breast height (DBH) and root biomass, and DBH and root length for both species. For root decay incidence of crop trees, there was no difference between PCT and UT stands for either species. It was shown that butt decay proportion was the best predictor of variability of root decay incidence. Seventeen mature (10 PCT and 7 UT) and sixteen recently PCT spruce-fir stands were surveyed for butt decay incidence. In mature stands, no difference in thinning treatment was found for red spruce. In young stands, balsam fir live-tree butt decay incidence was higher than its stump decay incidence. Sixty red spruces and balsam firs (half in PCT and half in UT stands) were selected to test the effect of PCT on tree windfirmness. No difference was found between PCT and UT stands for either species.
Tian, Suzhong, "Effect of Precommercial Thinning on Root Development and Root and Butt Decay Incidence of Red Spruce and Balsam Fir" (2002). Electronic Theses and Dissertations. 2630.
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