黄河上游退耕地植被组成、结构及水保功能评价

 面对黄河上游地区生态失衡的严重现实,作为植被恢复重建重要手段的退耕还林还草工程,其水保功能研究不仅具有理论价值,而且有十分迫切的实践需要。退耕地人工植被的建立,是一种仿拟自然植被的过程,植物种数越多,垂直层次性越复杂,植被的水保功能也越高。在黄河上游脑山区,物种丰富度指数最高的阶段,往往为植物群落演替的中间阶段,此时植物层次较多,一般可达3～5层,种类繁杂,生物基因保存多;同时,多层次的植物群落结构,对降水的截留作用明显,水保功能突出,以青海云杉为主的针阔混交类型,就是其典型代表之一。退耕地植被随着林分年龄增加,其水保功能逐步提高。一些退耕20多年的人工植被类型,生物多样性高,垂直层次结构复杂,水保功能甚至超过一些天然植被类型,直逼水保功能表现最好的50多年生天然青海云杉针阔混交林。在退耕还林还草工作中,通过仿拟自然植被结构,建造复层、混交的植被类型,来实现稳定的退耕地人工植被水保功能的整体思路,是切实可行的。

Evaluation to composing, structure and function for soil and water conservation of vegetation in rehabilitated lands in upper reach of the Yellow River

For the severe situation of eco-unbalance in the upper reaches of the Yellow River, the study of function for soil and water conservation in rehabilitated lands not only has the theoretical values, but has the urgent need for practice. The more the species and layers, the higher the function of vegetation. The research in the high mountains of the upper reaches of the Yellow River, shows that the high species richness appears in the middle stage of vegetation succession with more plant layers (usually 3～5 layers) and complex species and genes, and result in more rain reception and good eco-functions. In the implement of the project of Conversion of Cropland to Forest and Grassland, more attention should be paid to rehabilitate mixed conifer (mainly Picea crassifolia)and broad leaved trees in the middle stage of succession than such climax communities. As the vegetations grow, their structures and functions increase gradually. Some artificial vegetation types after 20 odd years in the rehabilitated lands have more bio-diversity, complex vertical layers of community, with so good eco-functions that even surpassing some of native vegetation, and approaching to the best one of eco-function in the areas, namely, 50 odd years native mixed Picea crassifolia with broad leaved trees. In the process of PCCFG, it is pressing and feasible to realize the whole function of artificial vegetation in the rehabilitated lands by means of imitating native vegetation structure for restoration of mixed and complicated vegetation types.