Some Arguments on the Forest Ecohydrological Effects
CHEN Ren sheng, KANG Er si, YANG Jian ping, ZHANG Ji shi, WANG Shu gong(Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou Gansu 730000, China)
Forest ecohydrological effects have been studied worldwide, and are important for ecological environment construction. However, there are some arguments on these effects all over the world. They are whether the forest can increase the vertical precipitation, whether the forest can increase the total runoff, whether the forest can adjust the peak discharge, whether the forest can increase the lower water, whether the forest works on foundation-head conservation, etc. The authors hold that there are some balancing processes in forest environment, and some of these processes are helpful for ecological environment, while some are harmful. In different regions, under different climate conditions, with different land surface, the balancing processes are different. Therefore, there have different forest ecohydrological effects. when the forest adjusting capacity is saturated, a little effect can result in the balancing process to anther balancing process. When the forest adjusting cupacity is not saturated, the balance could not be changed easily. That is to say, in the regions with well ecological environment, for example in rain forest regions, the ecological environment could not be changed easily. While in the regions with vulnerable ecological environment, for instance in arid regions of Northwest China, the ecological environment can be changed easily. The forest canopy interception process is continuous and dynamic, the interception storage depends on the amount of precipitation, rainfall intensity, rainfall duration, rainfall process, stand structure, closing of crop, density of leaf canopy, etc. The forest canopy interception process should be represented by interception storage capacity, interception storage and interception storage percentage. The interception storage can be observed in a special forest for a special precipitation process, the interception storage percentage can also be calculated, while the interception storage capacity could not be got easily. In a precipitation process, there will be rainfall in the forest before the interception storage comes to capacity. Therefore, there should be critical interception storage. In forest ecohydrological studies, the usual method is using contrastive basin. However, a favorable contrastive basin could not be found easily. This may result in different conclusions. In the experiments, there are some man-made factors that may affect the results. The analytical methods of the experimental results are statistical methods in forest hydrology. These methods could only find the elementary relationships among some possible factors that may affect the forest ecohydrological effects, they could not give the essential reasons, and in some situations, the statistical results may ignore the real processes. Therefore, in forest hydrology, the process study should be most important. Firstly, in the experimental site scale, working over the hydrological cycle process and the vegetation effects in soil-vegetation-atmosphere continuum with different surface features, to create a processing model. Secondly, undertaking the up-scaling process, changing the site scale to basin and region scale, combining with the GCMs, to create a watershed or regional distributed hydrological model. Based on the model, one can know the regional forest ecohydrological effects and its influence factors.