Partitioning And Chemistry Of Rainfall In Evergreen Broad-leaved Forest In Tiantong

The forest vegetation is of great significance to rainfall distribution and regulation of runoff.Entered the forest,rainfall is distributed into interception, throughfall and stemflow,which constitute a new water distribution pattern. From the aspects of forest structure and hydrological processes,this paper observed the hydrological characteristics of the Castanopsis fargesii forest and Schima superba forest,compared the redistribution of rainfall and nutrient cycling in the two communities,and provided a scientific basis to further understand the hydrological ecological functions of the two communities.Main results are as follows:(1)Structural characteristics:The tree density of schima community is significantly higher than castanopsis community.And DBH,tree height and biomass of castanopsis community are significantly higher than those of schima community,and the canopy density is also higher than that of schima community.The number of medium DBH individuals of C.fargesii is the most in castanopsis community,and the individuals show asymmetric distribution of the single peak.In schima community,S.superba of 10-15 cm in diameter at breast height is the individual that tracks the largest number of bands,and the individuals also show a distribution of single peak.The current development trends of the constructive species in the two communities are both mature and stable.There are two obvious sublayers in C.fargesii,23-24 m layer and 19-20 m layer,in castanopsis communities.The height of S.superba can also be two sublayers,the higher layer of S.superba is close to the lower layer of C.fargesii.The height of S.superba shows a single layer in schima community.From the tree layer structure,castanopsis community is better than schima community. (2)The maximum water holding capacity:The natural water content of C.fargesii branches and leaves are lower than that of S.superba.The water saturation deficit of C.fargesii leaves is lower than that of S.superba.And the water saturation deficit of castanopsis branches is higher than that of schima branches.The water absorption rate of branches and leaves decreased rapidly as time goes by. The early decrease amplitude is significantly,and reduces in the later.The function of canopy water storage plays the most prominent role in 1/2 hour, then the water absorption rate of branches and leaves drop to a lower level.Water absorption capacity of litter increases as time goes by,and water absorption rate decreased.The water storage function is the most prominent in the beginning 4 hours.The canopy maximum water holding capacity of castanopsis community is significantly higher than that of schima community,and the litter maximum water holding capacity of castanopsis community is lower than that of schima community.The surface litter in castanopsis community is looser than the surface litter in schima community.The function of water retention of the surface litter in castanopsis community is larger than that in schima community.(3)The redistribution of rainfall in the canopy:The trends of throughfall,stemflow and interception with time are basically the same with rainfall trend,and also the throughfall percentage and stemflow percentage.Interception percentage is in reverse with rainfall. Throughfall,stemflow and interception are highly significantly correlated with rainfall.The redistribution of rainfall is interacted by rainfall characteristics and forest features.In different communities,the main factor,which effects throughfall is the canopy structure,such as community density,distance between observation point and the trunk, branching angle of trees.These factors lead to differences between throughfall in castanopsis communities and that in schima community.In the same community,throughfall in different observation points is closely related to openness and LAl.Throughfall and throughfall percentage are smaller at the observation points with higher openness and smaller leaf area index.In the same community,DBH is the main factor that leads to different single tree stemflow.And in different communities,stratification of the tree layer leads to the differences of single tree stemflow of the same species.Interception and interception percentage are effected by rainfall and was significantly related to throughfall and throughfall percentage.(4)The chemical characteristics:With plenty of rainfall in summer,pH value of throughfall and stemflow are significantly higher than that in winter and spring,the less rainfall season. Evergreen broad-leaved forest in Tiantong,in which C.fargesiiand S. superba are constructive species and dominant species,has a buffer capacity for acid rain.The order of pH value is throughfall＞rainfall＞stemflow.There is no significantly difference between pH value of throughfall in castanopsis community and that in schima community,pH value of stemflow in castanopsis community is significantly lower than that in schima community.Nitrate nitrogen in throughfall and stemflow is obvious enrichment.Apart from a few cases,the order of the nitrate nitrogen concentration is stemflow＞＞throughfall＞rainfall.Nitrate nitrogen concentration of throughfall and stemflow are closely related to that of rainfall.And the nitrate nitrogen concentration of rainfall in stand is directly affected by rainfall.There are negatively significantly correlation between them.In addition,rainfall intensity,acidity,branches secretions and other factors effect nutrient concentration and nutrient input of rainfall in stand and outer together,thus affecting leaching amount of forest system.There is no significant difference between nitrate nitrogen concentration of throughfall in castanopsis community and that in schima community.And nitrate nitrogen concentration has a significant difference between the two communities.Nitrate nitrogen concentration of stemflow in castanopsis community is higher than that in schima community.There are obvious differences between nitrate nitrogen inputs of rainfall in stand and outer in evergreen broad-leaved forest of Tiantong.Nitrate nitrogen inputs of rainfall,except in January,are higher than that of throughfallo According to the net nitrate nitrogen flux,the nitrate nitrogen of rainfall is directly absorbed by two communities on January.(5)Rainfall is the main factor that leads to the differences of rainfall in stand among areas.Throughfall percentage of evergreen broad-leaved forest in Tiantong is basically the same with the average value of other areas, and interception percentage is slightly higher than that in other areas. These indicate that the rainfall interception capability of evergreen broad-leaved forest in Tiantong is at the middle level among all the evergreen broad-leaved forests in China.Evergreen broad-leaved forest in Tiantong has a cushioning action on acid rain,and among all evergreen broad-leaved forests,its enrichiment on H~+ in stemflow is the strongest.