美国大部分天然林经历过采伐利用。东北部森林以往实施择伐方式 ,优质林木被择伐后 ,残留下的是劣质林木。虽然西部天然林开发较晚 ,但次生林的状况同样令人担扰。总之 ,全国天然林区均充塞着小径林木和非理想树种的林木。为了优化天然林资源结构 ,必须充分开发利用这类低值原? Most of the natural forests in the United States have undergone harvesting. In the past, the northeast forest was implemented with selective cutting methods. After the high-quality forest trees were selected for cutting, the inferior trees were left behind. Although the development of natural forests in the western part of the country is relatively late, the situation in the secondary forests is equally disturbing. In a word, natural forest areas in China are stuffed with small-diameter trees and non-ideal trees. In order to optimize the natural forest resource structure, we must fully exploit the use of such low-value original?