手法を比較

	ワイブル直径分布	林分密度指数
分野	林学	林学
系統	Process / pipeline	Process / pipeline
提唱年	1973	1933
提唱者	Robert Bailey	Louis Reineke
種類	probability distribution	density measurement
原典	Bailey, R. L., & Dell, T. R. (1973). Quantifying diameter distributions with the Weibull function. Forest Science, 19(2), 97–104.	Reineke, L. H. (1933). Perfecting a stand-density index for even-aged forests. Journal of Agricultural Research, 46(7), 627–638.
別名	Weibull distribution, size-class distribution	SDI, Reineke density index
関連	1	2
概要	The Weibull diameter distribution is a flexible three-parameter probability model used to describe the size-class distribution (proportion of trees by diameter class) in forest stands. Introduced by Bailey and Dell in 1973, the Weibull function provides an excellent fit to observed diameter distributions across diverse forest types and management histories. It is widely used in growth simulators, yield models, and forest inventory analysis because it can capture a variety of distribution shapes (right-skewed, near-normal, and even multi-modal) with just three parameters.	The Stand Density Index (SDI), introduced by Reineke in 1933, is a dimensionless measure of forest density that accounts for both tree number and size. It expresses the number of trees per hectare in a stand, adjusted to a reference quadratic mean diameter (QMD) of 25 cm, providing a standardized metric for comparing tree density across different forest types and sizes. SDI is widely used in forest management to assess stocking levels and to guide thinning decisions.