长江上游森林植被变化对削洪减灾功能的影响

长江上游具有形成暴雨洪水的地形与气候条件，森林植被削洪减灾功能的提高必须着眼于森林植被—土壤生态系统结构的改善，削洪减灾功能的提高是通过林冠层、枯枝落叶层和土壤层对雨水的截留拦蓄作用实现的。研究区森林植被—土壤生态系统区域差异明显，不同地区该系统林冠层、枯枝落叶层和土壤层的最大截持水量不同，该系统削洪减灾功能的大小不仅与降雨特点有关，而且与系统各水文层前期持水量有关。在连续长时间暴雨情况下，森林植被—土壤生态系统除对第一次洪峰有削减作用外，对后续暴雨洪水的削减作用不明显，甚至会使洪峰增高。根据宜昌站30d洪水量的地区组成和森林植被—土壤生态系统截留持水功能的特点，提出了长江上游森林植被恢复、重建与保护的宏观调控对策。

Effect of forest vegetation change on function of flood drop and hazard reduction in upper reaches of the Yangtze River

There are topographical and climatic conditions for formation of rainstorm flood in the upper reaches of the Yangtze River. Raise of function of flood drop and hazard reduction of forest vegetation should be based on im- provement of forest vegetation-soil ecosystem structure and on function of retention water of forest canopy, litter and soil of this system. Regional differences of function of flood drop and hazard reduction of the forest vegetation-soil e- cosystem are very obvious. Maximum retention water of forest canopy, litter and soil of the forest vegetation-soil e- cosystem varys from place to place. Function of flood drop and hazard reduction of this system is related to feature of rainfall and to amount of retention water of forest canopy, litter and soil in earlier stage. Function of flood drop and hazard reduction of the forest vegetation-soil ecosystem will be decreased, and lost under continuous rain- storm. According to the regional distribution of 30 day's amount of flood in Yi Chang Hydrological Station, and characteristics of retention water function, countermeasures on macroscopically regulating and controlling restora- tion, rehabilitation and protection of forest vegetation of the upper reaches of the Yangtze River is suggested.