Effects of light and microsite conditions on tree size of 6-year-old Cryptomeria japonica planted in a group selection opening |
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Authors: | Toru Kohama Nobuya Mizoue Satoshi Ito Akio Inoue Kotaro Sakuta Hiroyuki Okada |
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Institution: | (1) Faculty of Agriculture, University of Miyazaki, Miyazaki, Japan;(2) Laboratory of Forest Planning, Faculty of Agriculture, Kyushu University, 6-10-1, Hakozaki, Higashiku, Fukuoka 812-8581, Japan;(3) Faculty of Agriculture, Tottori University, Tottori, Japan;(4) Faculty of Agriculture, Kyushu University, Fukuoka, Japan;(5) Sumitomo Forestry Co., Ltd., Tokyo, Japan;(6) Present address: Omura, Nagasaki, Japan |
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Abstract: | We examined the extent to which direct and indirect measures of light and microsite conditions could explain variation in
tree height and diameter at the base of 6-year-old Cryptomeria japonica trees planted in a group selection opening of about 0.32 ha on a steep slope at Shiiba, Miyazaki Prefecture, southern Japan.
We first used the gap light index (GLI) and soil thickness (ST) as directly measured indices. For an indirect measure of light, we used a between-cohort competition index (BCI) estimated from the position and total height of residual trees. For indirect measures of microsite, we examined topographic
indices (slope, plan and profile curvature, average slope gradient, and relative elevation) derived from digital elevation
models (DEMs) with different resolutions ranging from 2 to 10 m. The multiple linear regression using GLI and ST explained about 45% of variation in tree size, while simple regression using only GLI explained about 35%. The contribution of ST was about half of GLI. The multiple regressions using BCI and the topographic indices did not explain any more variation than using BCI alone (R
2 of about 0.26). We conclude that microsite conditions with shallower soil and steeper slope have negative effects on tree
growth in group selection openings, although the relative importance is smaller than light conditions. More comprehensive
studies considering several openings with more heterogeneous topography including different species are needed to generalize
our growth prediction using the indirect measures, which are useful for practical forest management. |
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Keywords: | Competition index Digital elevation model Gap light index Soil thickness Topographic indices |
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