| Longji terrace in Guangxi is a typical representative of rice terraces in south China,which had unique ecological landscape due to the particularity of terrace structure.As the only source of soil moisture,rainfall is the key factor that restricts the growth and distribution of plants in this area.In recent years,with the rapid development of tourism and the enhancement of human activities,vegetation had undergone significant changes,and vegetation degradation and soil collapse in some regions had become increasingly serious.The security and stability of the ecosystem were threatened,and the weakening of its ecological barrier effect severely restricted the sustainable development of regional agriculture.Quantifying rainfall response characteristics of vegetation and soil moisture is helpful to reveal the hydrological process and service function change mechanism of forest ecosystem under the background of regional vegetation restoration and climate change.Based on remote sensing image data and soil moisture monitoring data,the changes of vegetation and soil moisture in Longji terrace of Guangxi were studied,and their response characteristics to rainfall were analyzed.The main conclusions are as follows:1.Based on Landsat data in 1993,2006 and 2019,the changes of vegetation coverage and its spatial distribution pattern were analyzed in Longji terrace.The results indicated that:(1)From 1993 to 2019,woodland and cultivated land were the main land use types in Longji terraces,and the vegetation coverage showed an overall increasing trend,with the average value of 0.78 for many years.(2)There was no significant difference between the distribution of vegetation coverage in different slope aspects.Vegetation coverage increased with elevation,and increases at first and then decreases with slope.Vegetation coverage was the lowest among all the areas in elevation of 300m～900m and slope of 0～8°,while vegetation coverage was the highest in the alpine region with the elevation of >1500m and the slope >25°.2.Based on MODIS data,the changes of vegetation NDVI and its relationship with rainfall and runoff were analyzed from 2001 to 2020 in Longji terrace.The results indicated that:(1)Rainfall,vegetation NDVI and runoff fluctuated greatly during the research period,with the maximum values occurring in June,August and July,and the minimum values occurring in December,February and December,respectively.(2)From 2001 to 2020,both NDVI and rainfall showed a trend of decreasing first and then increasing.The areas of vegetation improvement were larger than those of vegetation degradation.(3)The response of vegetation cover to rainfall had a strong lag effect.Vegetation change was relatively stable and had little effect on runoff,while rainfall can significantly affect runoff change.3.Based on the soil moisture in-situ monitoring data,the soil moisture changes of bamboo forest(natural slope),mixed forest(natural slope),chinese fir forest(artificial terrace),and terraced dry land(artificial terrace)and their response characteristics to rainfall were analyzed in Longji terrace.The results indicated that:(1)The stability of the soil layer had an impact on soil water storage in the vegetation.The larger the soil variation coefficient value,the more active the soil layer and the lower the water stored in soil.(2)The soil moisture of each vegetation showed an hysteresis response to rainfall with the oeder of chinese fir forest > terraces > bamboo forest > mixed forest.For 0-20 cm soil,the effective replenishment amount and rate of bamboo forest and terraces were higher than those of chinese fir forest and mixed forest,while for 40-60 cm soil,it was the opposite.When the amount of rainfall increased to a certain range,the effective replenishment efficiency of the soil moisture decreased.The effective replenishment efficiency of each vegetation was in the order: heavy rain > medium rain > rainstorm > large rain storm > light rain.In the rainy season,the mixed forest had high effective replenishment amount and rate and abundant soil water storage because of its high soil water retention performance and sensitive response to rainfall. |
