| Forest ecosystem is the second largest ecosystem in the world,with enormous economic,social and ecological benefits.Forests and water are inextricably linked.The litter layer and soil layer on the ground are used to intercept and store the precipitation,to redistribute and regulate the precipitation,and to play a unique hydro-ecological function.In this study,the main forest types of Pinus massoniana natural forest Mountain Basin,Pinus massonian),were selected in mountainous area of western Hunan.The forest hydrological processes of different forest types,such as canopy,litter layer and soil layer,were compared and studied in Eucommia ulmoides plantation,mixed maple camphor forest and sloping farmland as control.The effects of different stand types on water quality were studied by measuring the water quality of different stand types,such as penetrable rain,stem flow,surface runoff and soil flow,for the evaluation of hydroecological benefits of different vegetation types and the reasonable maintenance of ecological environment.The rational management of forests and the sustainable use of water resources provide the theoretical basis.The specific research results are as follows:(1)with the implementation of the project of returning cropland to forestry in small watersheds,the restoration and reconstruction of a large amount of vegetation has changed the local microclimate environment,increased rainfall,increased the effect of cooling and humidifying,increased the vegetation.The wind speed is decreased.The correlation coefficients of rainfall,humidity,and wind speed were positive correlation,and the correlation coefficient between wind speed,rainfall and humidity and wind speed and humidity were significantly negative correlation.The study area has abundant rainfall and suitable temperature and humidity,which is beneficial to plant growth.(2)The canopy interception of Eucommia ulmoides forest,maple camphor mixed forest and Pinus massoniana forest were 289.75mm,358.78mm and 351.46mm,respectively,and the canopy interception rates were 14.69%,18.19%and 18.79%,respectively.With the increase of rainfall,the penetration rate,trunk runoff rate and canopy interception rate of different vegetation types also increased with the increase of rainfall,the ratio of throughfall rainfall,the ratio of throughfall rainfall,the trunk runoff rate and canopy interception rate also increased with the increase of rainfall.With the decrease of rainfall,there was a significant positive correlation between rainfall and canopy rainfall,the amount of penetrating rainfall and canopy interception of mixed forest was larger than that of pure forest,and the trunk runoff of pure forest was larger than that of mixed forest.The distribution of rainfall in canopy of different vegetation types was the highest,followed by interception of canopy and minimum of trunk runoff.(3)Leaves were the main way of accumulation of litter in different vegetation types,followed by branches,with the smallest detritus,while the sloping farmland was different from the forest vegetation types,and the debris of sloping farmland was the third.The lowest was the way of fruit fall accumulation.The total thickness of litter in different vegetation types was the largest,and that of sloping farmland was the smallest.The total reserves of litter in Pinus massoniana forest was the largest(18.75t/hm2),followed by the mixed forest of maple camphor with 13.59 t/hm2,and the minimum in sloping farmland.The litter reserves of undecomposed layer and semi-decomposable layer were as follows:Masson pine forest>mixed maple camphor forest>Eucommia ulmoides forest>sloping farmland.There was a logarithmic relationship between litter retention capacity and soaking time of different vegetation types(R>0.93N).The relationship between water rate and soaking time was obvious power function(R>0.99).The order of water leakage in litter layer of different vegetation types was:Eucommia ulmoides Linn(1151.87 mm)>Pinus massoniana(1095.64 mm)>Maple Cinnamomum camphora mixed forest(1065.92 mm)>sloping farmland(908.11 mm).(4)In different vegetation types,the highest soil moisture content was in sloping farmland,followed by the mixed maple camphor forest and the lowest soil moisture content in Pinus massoniana forest.The order of soil non-capillary porosity of different vegetation was 4.50)>Eucommia ulmoides forest 3.55)>Pinus massoniana forest 3.50)>slope farmland 2.80%,the order of soil total porosity was the same as that of capillary porosity,all of them were maple camphor mixed forest>Masson pine forest>slope farmland>Eucommia ulmoides forest.The soil available water holding capacity of different vegetation types was the highest(364.50t/hm2),followed by Eucommia ulmoides forest,the smallest was sloping farmland,and the mixed forest was 3.25 times as high as the sloping farmland,and the order of soil capillary water holding capacity and maximum water holding capacity was the same.The soil initial infiltration rate of different vegetation types was the largest,the second was Eucommia ulmoides forest,and the smallest was sloping farmland,the first infiltration rate of different vegetation types was the highest,the second was Eucommia ulmoides forest,and the other was that of Pinus massoniana.There was a better power function relationship between infiltration rate and infiltration time in different vegetation types(R>0.89),the water content of different vegetation types showed significant difference,the largest water content was Eucommia ulmoides forest,the second was mixed forest of Acer camphora,and the lowest was sloping farmland.Before and after rainfall,soil moisture content was negatively correlated with wind speed and temperature,and soil moisture content was positively correlated with moisture content.(5)With the increase of rainfall,the surface runoff increases gradually,among which the Eucommia ulmoides forest land is extremely significant,and when the rainfall gradually increases to 30 mm,the surface runoff of sloping farmland remains the largest.When rainfall is more than 50 mm,there is a significant increase in surface runoff of the four types of forest land,which indicates that the soil water content begins to reach saturation,and the total runoff of different vegetation types,The order of runoff depth and runoff coefficient was Eucommia ulmoides>Pinus massoniana>sloping farmland>mixed stand of maple camphor camphor,under the same rainfall,the runoff was smaller with the increase of evaporation,and the total runoff of mixed forest was the smallest.The results showed that the evapotranspiration of mixed stands was the largest,and the surface runoff of different vegetation types increased with the increase of rainfall,and there was a significant linear relationship between surface runoff and rainfall.(6)Forest helps to purify water quality and improve water quality.The water quality of penetrating rain,trunk runoff,surface runoff and litter leakage has improved over time.Although some ions are decreasing,most of them are increasing.In view of the strong ability of forest vegetation to purify water quality,it is necessary to give full play to its role in protecting forests.(7)The hydrological function of different vegetation types is the best,the worst is sloping farmland,and the worst in the forest is Pinus massoniana forest,the order of which is mixed forest of Acer camphora>(15.42)>Eucommia ulmoides forest(7.15)>Pinus massoniana forest(2.55)>the slope farmland is-0.86.The broad leaved tree has stronger hydrological function,and the ability of soil and water conservation and water conservation is stronger than that of coniferous tree,but the water conservation capacity of sloping farmland is poor.(8)The results show that forest vegetation has the ecological functions of soil and water conservation,water conservation and water purification.The results provide theoretical support for the scientific evaluation of the water conservation function of different types of vegetation returning farmland to forest,and the protection and construction of forest ecology.The function of forest conservation of water,soil and water conservation,purification of water quality is further explained,which provides data support for ecological benefit evaluation of conversion of cropland to forest. |
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