| The unreasonable structure and sparse undergrowth of the forest in Taizi Mountain of Hubei Province,lead to the decrease of the interception effect of the forest on rainfall,serious soil erosion and degradation of the service function of the forest ecosystem,which hinder the regional ecological environment protection and economic construction.Therefore,it is of great significance to study the interception effect of different stands on rainfall and the influence of different forest layer structures on runoff and sediment yield on slope surface to restore forest ecological function.In this paper,five different stands in Taizi Mountain of Hubei Province,including pure Cupressus funebris forest,pure Pinus massoniana forest,Quercus acutissima and Acer mono mixed forest,Cupressus funebris and llex.purpuea Hassk mixed forest,Pinus massoniana and llex.purpuea Hassk mixed forest,were taken as the research object to study the interception effect of different stands on rainfall.Then four field runoff plots are established in different stands,and the four runoff plots are treated respectively(removing shrub grass layer,removing litter layer,removing shrub grass layer and litter layer and retaining natural state).A control field runoff is established on the bare land slope.The runoff and sediment yield characteristics of different runoff plots were analyzed by using the method of natural rainfall monitoring,and the following conclusions were drawn:(1)There are some differences in rainfall interception and redistribution among canopy layers of different stands.During the observation period,the throughfall of pure Cupressus funebris forest,pure Pinus massoniana forest,Cupressus funebris and llex.purpuea Hassk mixed forest,Pinus massoniana and llex.purpuea Hassk mixed forest,Quercus acutissima and Acer mono mixed forest were 489.83mm,487.88mm,478.68mm,482.32mm and 470.27mmrespectively,accounting for 77.58%,77.27%,75.81%,76.39%and 74.48%of the total atmospheric rainfall,and the stemflow was 24.48mm,24.86mm and27.09m,respectively m.25.96mm and 30.12mm,respectively,account for 3.88%,3.94%,4.29%,4.11%and 4.77%of the total amount of atmospheric rainfall.The amount of canopy interception is 117.10mm,118.66mm,125.63mm,123.12mm and 131.02mm,respectively,accounting for 18.55%,18.79%,19.90%,19.50%and 20.75%of the total amount of atmospheric rainfall.The interception effect of canopy layer on rainfall is as follows:Quercus acutissima and Acer mono mixed forest>Cupressus funebris and llex.purpuea Hassk mixed forest>Pinus massoniana and llex.purpuea Hassk mixed forest>pure Pinus massoniana forest>pure Cupressus funebris forest.The density and canopy density of five kinds of stands are similar,indicating the canopy interception effect:broad-leaved mixed forest>coniferous and broad-leaved mixed forest>pure coniferous forest.The amount of penetrating rainfall,trunk stem flow,and canopy interception in different stands are all positively related to rainfall,and they increase with rainfall.There is a linear relationship between stem flow and rainfall,and there is a logarithmic function relationship between canopy interception and rainfall.(2)The characteristics of shrub grass layer and litter layer were different in different stands.The biomass of shrub and grass layer in pure Cupressus funebris forest,pure Pinus massoniana forest,Cupressus funebris and llex.purpuea Hassk mixed forest,Pinus massoniana and llex.purpuea Hassk mixed forest,Quercus acutissima and Acer mono mixed forest were 5.64t/hm~2,6.68t/hm~2,6.12t/hm~2,5.03t/hm~2,6.89t/hm~2respectively,the maximum water holding capacity is 12.59t/hm~2,13.61t/hm~2,13.36t/hm~2,11.49t/hm~2 and 14.12t/hm~2 respectively;the reserves of litter layer are 4.85t/hm~2,7.45t/hm~2,8.25t/hm~2,8.05t/hm~2 and 9.60t/hm~2 respectively;the maximum water holding capacity is 9.33t/hm~2,11.43t/hm~2,14.79t/hm~2,14.20t/hm~2 and 15.49t/hm~2respectively.There is a positive correlation between the maximum water holding capacity and biomass in the shrub grass layer of different stands.The larger the biomass of shrub grass layer,the stronger the water holding capacity.The reserves of litter layer in different layers of five kinds of stands are shown as follows:undecomposed layer>semi-decomposed layer,and the maximum water holding capacity of litter layers of different layers is expressed as:semi-decomposed layer>undecomposed layer,it is because most of the semi-decomposed layer is litter that is decomposed to a certain degree,and its water absorption capacity is greater than that of litter in the undecomposed layer.The reserves and maximum water holding capacity of litter in five kinds of stands are as follows:Quercus acutissima and Acer mono mixed forest>Cupressus funebris and llex.purpuea Hassk mixed forest>Pinus massoniana and llex.purpuea Hassk mixed forest>pure Pinus massoniana forest>pure Cupressus funebris forest,which shows that the litter reserves and maximum water holding capacity are:broad-leaved mixed forest>coniferous and broad-leaved mixed forest>pure coniferous forest.(3)There are differences in runoff and sediment yield in different forest layer structures.The amounts of runoff and sediment yield in the runoff plot under the natural condition are as follows:bare land>pure Cupressus funebris forest>pure Pinus massoniana forest>Pinus massoniana and llex.purpuea Hassk mixed fores>Cupressus funebris and llex.purpuea Hassk mixed forest>Quercus acutissima and Acer mono mixed forest.Under different treatment methods,the amounts of runoff and sediment yield in runoff plots are as follows:removal of litter and shrub layer>removal of litter layer>removal of shrub layer>natural state plot.The runoff yield of Bare land runoff plot is about 4.6-6.0times of that of natural runoff plot,and the sediment yield is about 12.0-15.5 times.After the removal of shrub and grass layer,the increasing flow rate is about 12%-15%,and the increasing sand rate is about7%-10%;after the removal of litter layer,the increasing flow rate is about 113%-128%,and the increasing sand rate is about 99%-113%;after the removal of shrub and grass layer and litter layer,the increasing flow rate and the increasing sand rate are about 200%.It shows that litter layer plays a significant role in reducing runoff and sediment,and shrub grass layer has a low contribution rate to the function of soil and water conservation.The function of soil and water conservation is the strongest in the stand with complete structure.(4)The effect of rainfall and rainfall intensity on runoff and sediment yield on forest land slopes.Runoff plots under different treatments in different forests have a linear positive correlation between runoff depth and rainfall,and a positive quadratic positive correlation between runoff depth and rainfall intensity.There is a linear positive correlation between sediment yield and rainfall,and a positive quadratic positive correlation between sediment yield and rainfall intensity.By comparing the effect of rainfall on runoff sediment yield,it is concluded that the sensitivity of runoff yield to rainfall is slightly greater than that of sediment yield to rainfall.By comparing the impact of rainfall intensity on runoff sediment yield,it is concluded that the sensitivity of sediment yield to rainfall intensity is slightly greater than the sensitivity of runoff yield to rainfall intensity.And in areas where the surface is bare and uncovered,runoff and sediment yield have the greatest correlation with rainfall and rainfall intensity. |
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