一、引言森林生态系统是陆地生态系统的一个重要组成部分,它既可改善农业的生产条件,又可给人们提供良好的生活环境,是维持自然生态平衡的一个重要因素。在我国华北平原和沿海平原地区,林粮间作的方式可分为路林、沟渠林带网格的复合系统和混农林业系统,其中林木可起保持水土,防 I. INTRODUCTION Forest ecosystem is an important part of terrestrial ecosystem. It can not only improve agricultural production conditions, but also provide people with a good living environment, which is an important factor to maintain the natural ecological balance. In China’s North China Plain and the coastal plains, the intercropping of forest and grain can be divided into the compound system of forest road, ditch forest grid and agroforestry system, in which the forest trees can play a role in keeping water and soil, preventing