| It is a indisputable fact that the climate change, especially frequently extreme climate event can make a big impact to the forest ecosystem. Under the background of global change, hydroecology research has been one of the focus in the world, but the influence of forest structural change to hydrology function is the core of research for forest-water relations. In this paper, in the context of the destruction of forest ecosystem by2008frozen rain and snow disaster in south of China, we launched this scientific research to reveal influence of the change in forest structure to the forest hydrological processes. Choosing subtropical evergreen broadleaved forest which has the main dominant tree species Castanopsis fissa in Xiaokeng basin of Nanling mountain as the research target. The experiment was carried out through trimming canopy layer of Castanopsis fissa and added canopy detritus in one plot, trimming canopy layer of Castanopsis fissa and removed canopy detritus in another plot to simulate frozen rain and snow disaster destruction for forest ecosystem. Using the method of community ecology to investigate each kind of structure factor of undamaged and damaged forests at regular intervals, and to reveal the system structure space and time dynamic laws of damaged forest in its nature recovery process. During Apr2012to Mar2013period,12sample trees were selected with average tree method for stemflow measurement and14throughfall sampler were mechanically laid with grid method in damaged plot and control respectively, and the data of stemflow and throughfall obtained from46rain evens. On this account, the affects of canopy damage to re-distribution laws of precipitation were analysed. By the method of comparing paired runoff plots, the characteristics of slope surface runoff on damaged and undamaged forests and the main factors that influence the surface runoff were revealed. The main experiment results are as follows:(1) The canopy trimming takes a great impact on trees layer and understory structure. The research shows that, after1.5years, a massive branches start sprout at the top of the tree and the canopy start restore gradually in damaged forests, but compared with the uninjured forest during this period, the canopy density still has great disparity. After canopy trimmed, the coverage of under vegetation increase obviously, the species abundance and the biological diversity has remarkable enhancement. In addition, the constitute of tree seedings change largely yet, some pioneer species of sun plants such as Mallotus lour, Sapium discolor, Litsea cubeba grow rapidly, take over from Castanopsis fissa position and might change the direction of forest succession in the future.(2) Canopy triming influence the rainfall redistribution pattern significantly. Artificial measured total rainfall are1859.1mm during the experimental period, in which the canopy interception are385.2mm and the average canopy interception rate is20.7%; the total throughfall are1315.5mm and the average throughfall rate is70.8%; the total stemflow are158.4mm, and the average stemflow rate is8.5%in the control plot(CN). At the same time, the total canopy interception, throughfall and stemflow in the damaged forest of TD (trimming canopy+canopy detritus adding) are238.7mm,1550.9mm and69.5mm respectively. The average canopy interception rate, throughfall rate and stemflow rate are12.8%,83.5%and3.7%respectively. The canopy trimming treatment take obvious impaction on the rainfall redistribution, and the main performance increase the throughfall rate, but decrease the canopy interception rate and the stemflow rate.(3) Factors affacting precipitation redistribution pattern. The study result shows that, for two types of forests, the amounts of canopy interception, throughfall and stemflow have obvious positive relations with rainfall. Among them, the canopy interception is logarithm correlation to the rainfall,the throughfall is liner correlation to rainfall and the stemflow is binomial related with rainfall. However, the canopy interception rate is negative exponentially related with rainfall. The throughfall rate is binomial related with rainfall, and the stemflow present positive logarithm relevant to rainfall. By the contrast analysis, we find that rainfall and tree layer crown density are the main factors which had impaction on the canopy interception, throughfall and stemflow.(4) The maximum interception capability of the forests. Study found that, the maximum interception amount of undamaged Castanopsis fissa community is21.3mm. Among them, the maximum of canopy interception is20.2mm; the maximum interception of under vegetation is0.5mm and the maximum water-holiding capacity of litter layer is0.6mm. Compared with the undamaged forest, the forest of Castanopsis fissa community after trimmed the canopy (TD), the maximum interception capacity is decreased obviously, only9.9mm, however the maximum interception of under vegetation (1.6mm) and litter layer (3.5mm) are increased significantly.(5) The research of biomass and water-holiding capacity for forest floor. The total biomass of bushes and herbs have great difference in different treatment plots. the total biomass of TD is the largest, reached8.75t/hm2; next is TR (trimming canopy+canopy detritus removing), reached6.26h/hm2; the smallest is CN,which is only2.53t/hm2. The biggest water capacity performance is TD (15.71t/hm2)> TR (11.31t/hm2)> CN (5.06t/hm2).The litter layer storage of different treatment plots performed TD (46.20t/hm2)>CN (3.74t/hm2)> TR (2.56t/hm2).The biggest water capacity is TD (35.11t/hm2)> CN (6.28t/hm2)> TR (5.63t/hm2); and the biggest capacity rate is TR(222.7%)> TD(175.2%)> TD(172.6%). The branches water-holding capacity is lower than the leaves in TD plot. The water-holding speed has remarkable index correlation with the soaked time.(6) Canopy trimming affect the slope surface runoff and sediment significantly. In three different treated plots the slope runoff and soil erosion are characterized by TR> CN> TD. That is, canopy trimming and canopy detritus removing (TR) can significantly increase the slope surface runoff and soil erosion, whereas, canopy trimming and canopy detritus adding (TD) can obviously reduce them.With grey incidence degree analysis, the dominant factors which influenced slope surface runoff are precipitation, rainfall duration, crown density of tree layer, biomass of litter layer and the effectively water-holding quantity of litter layer. The precipitation, tree layer crown density and litter layer thickness affect the sediment erosion. |
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