Comparison of the modified Weibull and Richards growth function for developing site index equations |
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| Authors: | Buan Payandeh Yonghe Wang |
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| Institution: | (1) Natural Resources Canada, Ontario Region, 1219 Queen Street East, P6A 5M7 Sault Ste. Marie, Ontario, Canada |
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| Abstract: | A site index model based on the Weibull cumulative distribution function was fitted to three stem analysis data sets of black spruce (Picea mariana (Mill) BSP), white spruce (Picea glauca (Moench) Voss) and aspen (Populus tremuloides Michx.). The resulting equations were compared with those based on the modified Richards' (1959) biological growth function (Ek 1971; Payandeh 1977, 1978). The Weibull-type model performed as well as or better than the biological growth function for white spruce and aspen, respectively, but it performed less accurately in the case of black spruce. The Weibull-type model appears to behave better, i.e., it produces more realistic height growth patterns, than the Richards function upon extrapolation particularly at young ages. |
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| Keywords: | stem analysis data site index model black spruce white spruce aspen |
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