Effects Of Vegetation Restoration On Soil Moisture On Slopes In Karst Area And Its Influencing Factors

Study of the effects of natural vegetation restoration on soil moisture in karst area is of great significance to the study of hydrological process of the area,as well as the prevention of rocky desertification,soil and water conservation,and vegetation restoration.Method of substitution of space for time was used,and experiment plots of cultivated land,grassland,shrubland and woodland were set on slope in karst area,respectively representing different stages of natural vegetation restoration.Soil moisture in each experiment plots was monitored at 4 soil layers(5cm,10cm,15cm and 20cm,respectively),and soil,roots,and litter samples were collected and their properties were measured.Meteorological elements,vegetation interception and soil evaporation in the study area were monitored.Soil moisture indicators were calculated to reflect the average level,temporal variation characteristics,and response to meteorological elements of soil moisture.Environmental factors such as vegetation interception,soil properties,soil evaporation,root content,which are significantly different between different vegetation restoration stages,were used as explanatory variables.The main indicators reflecting soil moisture characteristics were selected as response variables.Main influence factors of effect of vegetation restoration on soil moisture were recognized by multiple linear regression,and the mechanisms of these main influence factors were explanated.The main conclusions are as follows:(1)The average levels and temporal variations of soil moisture in each vegetation restoration stage were different.From the cultivated land to the grassland stage,the average level of soil moisture(28.56%and28.04%,respectively)and temporal stability of soil moisture(temporal variation coefficients of 10.50%and 11.00%,respectively)have no obvious changes,and the soil profile difference of soil moisture decreased obviousy.From the grassland to the shrub stage,the average level of soil moisture increased(29.86%in the shrub stage)and the temporal stability of soil moisture also increased(temporal coefficient of variation in the shrub stage was 9.60%).From the shrub to the forest stage,the average level of soil moisture decreased(27.42%in the forest stage),which was lower than the cultivated land and grassland,and the temporal stability of soil moisture becomes weaker(11.50%in the woodland stage),which was lower than the cultivated land and grassland.(2)The responses of soil moisture to rainfall and temperature were different in different vegetation restoration stage.In terms of response to rainfall,from the cultivated land to the grassland stage,the increase in soil moisture during rainfall increased(0.83%to 1.87%),and the peak time became earlier(26.29h to 19.46h).From the grassland to the shrub stage,the increase in soil moisture during rainfall decreased(1.06%in the shrub stage),and the peak time became later(shrub stage is 21.42h).From the shrub to the woodland stage,there is no obvious change in the increase of soil moisture during rainfall(1.05%in the woodland stage),and the peak time became later(28.63h).In terms of response to temperature,from the cultivated land to the grassland stage,the decrease in soil moisture during the heat and dry period increased(-0.40%to-0.97%).And,from the grassland to the woodland stage,it shrank(-0.47%and-0.37%in shrub and woodland land,respectively).(3)The main influencing factors of soil moisture effect included vegetation interception rate,soil properties,soil evaporation and root content,etc.The most important soil properties were non-capillary porosity,saturated hydraulic conductivity,and clay content.The increase of non-capillary porosity during vegetation restoration can explain the decrease of the minimum value(R~2 change=0.381)and the average value(R~2 change=0.232)of soil moisture,and the increase of the range of soil moisture(R~2 change=0.149)and the increase of the increase in soil moisture during rainfall(R~2 change=0.140).The increase of saturated hydraulic conductivity can explain the increase of the minimum value(R~2change=0.155)and the average value(R~2 change=0.084)of soil moisture,and the decrease of the range of soil moisture(R~2 change=0.168).The decrease of clay content can explain the increase of the average value(R~2change=0.274),the minimum value(R~2 change=0.176)and the maximum value(R~2 change=0.133)of soil moisture,and the decrease of the profile difference(R~2 change=0.237).The increase of root content can explain the decrease of the average value of soil moisture to a certain extent.The interception rates of shrubs and woodland were 10.76%and29.08%,respectively.And,the upward trend of vegetation interception rate resulted in a decrease of the increase in soil moisture during rainfall,which was more obvious in condition of low rainfall intensity.Vegetation interception rate is low when the rainfall intensity is large,so that the effect of the vegetation interception rate on the increase of soil moisture during rainfall was reduced.Under the same temperature conditions,the near-surface temperature generally showed a downward trend with vegetation restoration,resulting in reduced soil evaporation(0.70mm/h,0.56mm/h,0.54mm/h,0.47mm/h from the cultivated land to the forest land respectively).(4)In general,during the process of vegetation restoration,the average level and temporal stability of soil moisture did not change much from the cultivated land to the grassland stage,but the increase in soil moisture during rainfall increased and the response time of soil moisture became earlier.The average level and temporal stability of soil moisture increased to the highest from the grassland to the shrub stage,and the increase in soil moisture during rainfall decreased,and the response time of soil moisture became later.The average level and temporal stability of soil moisture decreased to the lowest from the shrub to the woodland stage,and the response time of soil moisture became later.And,the decrease in soil moisture during the high temperature and dry period shrank.In summary,vegetation restoration affected the average level,temporal changes,and the response characteristics to meteorological elements of soil moisture.The highest soil moisture average level and the strongest soil moisture temporal stability appeared in shrubs.Therefore,shrub was the most suitable vegetation type for soil moisture retention.