Abstract: A practical investigation of the five main tree species’ diameter, Larix Principis-rupprechtii, Chinese Pine, Populus davidiana, Betula platyphylla, Quercus Liaotungensis, is conducted in Pangquangou Nature Reserve. The χ² test and curve distribution trend are used to ascertain if they obey the normal distribution. To the tree species, the maximum likelihood estimation and minimum risk equivariant estimation are used to estimate the unknown parameters. The analysis and comparison of the above two methods show that the result of minimum risk equivariant estimation in fitting the stand forest diameters is more precise. The result indicates that the diameters of Larix Principis-rupprechtii, Chinese Pine, Populus davidiana, Betula platyphylla belong to the normal distribution, while that of Quercus Liaotungensis does not. And dynamic prediction of the diameters of the trees obeying normal distribution in this area is also done.

Key words: Pangquangon Nature Reserve, χ² test, maximum likelihood estimation, minimum risk equivariant estimation