在森林经营中要做到森林不发生虫害,是一个值得林学家们注意的问题。美国密执安州北部的阔叶树林组成复杂,有单纯林;也有岩槭、红槭、黄桦、铁杉及椴树、黑樱桃等其他几种树种组成的混交林。在多树种的混交林内很少有严重的虫害发生。因 It is a question that should be paid attention to by forest scientists to prevent forest pests from occurring in forest management. The broad-leaved forests in the northern part of Michigan State of the United States are composed of complex forests with simple forests. There are also mixed forests consisting of rock maple, red maple, yellow birch, hemlock and lime trees, black cherry and other tree species. There are few serious pests in the mixed forest of many species. because