乔木在城市森林建设中的重要作用

城市森林对光、热、气、水、土等生态因子具有重要的调节作用，对城市的生态环境保护起着不可替代的作用。目前，我国城区生态建设所使用的树种普遍比较单一，造成城市绿化景观的单调。在城市森林建设中，要重构人与自然的关系，按照复合生态系统理论，以人为本，林水结合。选择城市乔木树种时，要按照适地适树的原则，尽可能应用乡土及野生树种，利用乔木尽快占领城镇空间，保证生态环境安全。提高枝下高到8m左右，就可营造出夏天降温，冬天充分享受阳光的公共场所。在城区广场的绿化中，要引入一些高大乔木，形成巨大的伞状树冠，以乔木为主组成乔、灌、藤、草结合的近似天然林，充分向空间要生态效益，是一条行之有效的捷径，还要增加攀缘植物的绿化比重。攀缘植物有较强的适应性、耐旱性和吸附攀缘能力，不仅是荒漠化土地、荒山、沟壑恢复植被的先锋植物，而且也是城市绿化、桥梁美化、道路护坡的优良绿化植物。

Discussion on Important Role of Trees in Urban Forest

Since conducting the policy of opening and reform, urbanization is speeding in China, which helps socioeconomic development. However, environmental problems become vital as well. In the viewpoint of ecology, urban forest,which mainly consist of trees,plays an important role on the adjustment of eco-elements such as light, heat, gas, water and soil as well as protects urban-rural eco-environment. At present tree species applied in urban forest usually are monotonous, which makes city landscape looks dull. Thus the relationship between human and nature must be reformed in urban forest construction, and according to compound ecosystem theory human is the prime. For building urban forest, trees must integrate with water. Tree species selection must follow the principle of trees adapted to site conditions and employ local and wild plants especially trees so as to as early as possible expand spatially. According to measures when first branching reaches 8 m, the surroundings could be created that lower temperature in summer and fine sunlight in winter. Hence in city square construction some high trees must be planted together with scrubs, lianas and herbs so that huge umbrella-ship crown could be formed and bring ecological benefits spatially. Additionally climbers must be paid attention as are characterized with wide adaptation, strong drought tolerance and climbing capacity, so that they are not only applied in greening dessert, bare mountain and hills, also in urban area, bridges and roads.