Abstract
Khilmi’s self-thinning model of a Gompertz function is a practical model, but generally it is difficult to estimate a self-thinning parameter. The purpose of this paper is to estimate parameters with existent material. First, we attempt to estimate the parameters by a supposition used to express a self-thinning curve on a stand density control diagram. The result was as follows: the self-thinning parameter is only concerned with height curve parameters. If height curve is expressed with a Gompertz function, the self-thinning parameter is equal to the time coefficient. In addition, when a height curve is expressed with a Richards function, the same result was gotten with a supposition. Then we tested this result with Spurr et al.’s self-thinning data and Usoltsev’s yield table. When we applied stand density and height for growth function independently, we couldn’t confirm a relationship between the self-thinning parameter and the time coefficient of the height curve. However, when we applied stand density with fixed parameters except end density, AIC of the model didn’t increase. Finally, we compared Khilmi’s self-thinning model expressed by these parameters with a self-thinning model on a stand density control diagram—Tadaki’s model. These two curves are close to each other before crossing the full density curve.
