| Water and soil erosion is one of the three big environment disasters.The present situation of water and soil loss is serious,and it need to be sloved for giving a heavy burden on social prodution and people's living.But many studies mainly focused on the loess plateau region of northwest,black soil region of northeast and karst mountain area of southwest,and less research focused on the red soil region of southern China.Nanling Mountains is located in climate demarcation line of the middle subtropics and south subtropics.It is an important center for biological diversity,and plays an important role in protecting the regional ecological environment.Our study is located in Xiaokeng National Forest Park,and chose four vegetation types(bareland,grassland,shrubbery,and evergreen broad-leaved forest).We have set up rain measuring cylinders and slope runoff plots for continuous monitoring of individual rainfall characteristics,precipitation distribution,slope runoff and sediment loss.These datas allow us to analysis the relationship of rainfall and slope runoff in different vegetation types,and expound the mechanism of the differences,in this way can we find dominant factors influencing the slope soil and water loss.Furthermore,removing shurb-grass layer and litter layer of evergreen broad-leaved forest to calculate the impact to rainfall precipitation distribution and contribution rate to slope runoff and sediment loss.Finally,we can make clear the dynamic change of hydrological effect and its soil and water conservation function,which is caused by vegetation change.At the same time,the results can also provide the basis data for further analysis and evaluation of the subsequent hydrological effects of heavy 2008 Chinese ice storm disaster,and provide theoretical basis for assessment of nanling forest hydrological ecological service function and regional water resources management.Main study results as following:(1)The amount of annual rainfall is 1631.3 mm in the study area,and it is well distributed.From April to October 2015,we collected a total of 47 individual rainfall data,and mainly is small,moderate rain,but heavy storm is rarely,accounted for 29.12% and 29.22% of the total rainfall,respectively.(2)During the period of observation,from April to October 2015,the amount of rainfall is 1385.27 mm.The amount of throughfall in grassland,shrubbrey and evergreen broad-leaved forest respectively are 1025.71,1190.14 and 1062.93 mm,and its throughfall rate are74.04%,85.91% and 76.73% respectively.Sorted in order of size is: shrubbrey ? evergreen broad-leaved forest ? grassland.The amount of stemflow in shrubbrey and evergreen broad-leaved forest respectively are 92.56 mm and 167.16 mm,and its stem flow rate are 6.68% and 12.07%,respectively.The amount of canopy interception in grassland,shrubbrey and evergreen broad-leaved forest respectively are 359.56 mm,102.57 mm and 155.18 mm,and its canopy interception rate are 25.96%,7.40% and 11.20% respectively.Sorted in order of size is: grass-land?evergreen broad-leaved forest?shrubbrey.(3)A linear correlation is found between throughfall and rainfall.And a“J”type curve correlation is found between throughfall rate and rainfall.Throughfall rate shows spatial variability,and its coefficient of variation decreases with the increase of rainfall,then tends to a constant value.The threshold values of rainfall are: 10 mm(shurbbery),30 mm(grassland)and 50 mm(evergreen broad-leaved forest).The amount of throughfall in evergreen broad-leaved forest which is removed shrub-grass layer is 1114.81 mm,and in control group is 1011.04 mm.But by t test,the effects on throughfall is not significant(P?0.05)with removing shrub-grass layer of evergreen broad-leaved forest.(4)There has positive correlation between stemflow and rainfall,rainfall intensity,diameter at breast height of tree.The threshold values of rainfall which can produce stemflow in shurbbery and evergreen broad-leaved forest are 4.22 mm and 8.16 mm respectively.There have binomial or logarithmic relations between canopy interception and rainfall.And there has logarithmic relations between canopy interception rate and rainfall.(5)During the period of observation,the amount of slope runoff in bareland,grassland,shrubbrey and evergreen broad-leaved forest respectively are 124.25 mm,78.74 mm,49.42 mm and 82.71 mm.Bareland as control group,the slope runoff reduction rate of grassland,shrubbrey and evergreen broad-leaved forest are:36.63%,60.23% and 33.43% respectively.Sorted in order of size is: shrubbrey?grassland?evergreen broad-leaved forest.By t test,the amount of slope runoff between bareland and shrubbery is significantly different(P< 0.05).The amount of slope runoff in evergreen broad-leaved forest which is removed shrub-grass layer or litter layer is 96.36 mm and 223.14 mm,and the slope runoff increasement rate are:16.50% and 169.79%,respectively.Sorted in order of size is: removing litter layer?removing shrub-grass layer.By t test,the amount of slope runoff between removing litter layer and removing shrub-grass layer is significantly different(P< 0.05).This implies that litter layer in forest floor has more contribution for reducing slope runoff than shurb-grass layer.There has positive correlation between slope runoff and rainfall and rainfall intensity.Using grey correlation analysis,it is conclud that three main factors are: rainfall amount(0.75)= rainfall density(0.75)?litter biomass(0.64).(6)During the period of observation,the amount of slope sediment in bareland,grassland,shrubbrey and evergreen broad-leaved forest respectively are 93.69 t/hm2,33.91 t/hm2,39.08 t/hm2 and 18.44 t/hm2.Bareland as control group,the slope sediment reduction rate of grassland,shrubbrey and evergreen broad-leaved forest are:63.80%,58.29% and 80.33%,respectively.Sorted in order of size is: evergreen broad-leaved forest?grassland?shrubbrey.The amount of slope sediment of the removing shrub-grass layer or litter layer in evergreen broad-leaved forest are 18.56 t/hm2 and 23.50 t/hm2,and the slope sediment increasement rate are:1.19% and 28.52%,respectively.Sorted in order of size is: removing litter layer?removring shrub-grass layer.By t test,removing litter layer or shrub-grass layer has no significant impact on the amount of slope sediment(P?0.05).There has positive correlation between monthly slope sediment and rainfall.The distribution of monthly slope sedimentis not well-distributed.The maximum monthly slope sediment is in May,and the minimum is in October.Furthermore,compared with shrubbery and grassland,bareland and evergreen broad-leaved forest are more sensitive to heavy rainfall.And soil hydrological function of controling erosion decreases significantly in heavy rainfall. |
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