南方山区典型小流域桉树人工林种植对水土流失的影响

Impacts of Eucalyptus plantation on soil and water losses in a typical small watershed in mountainous area of southern China

南方山区人工林的不合理开发导致严重的水土流失。典型人工林小流域土壤侵蚀时空变化研究对于人工林种植和山区生态环境可持续发展具有重要意义。本研究利用地理信息系统结合修正通用土壤流失方程,分析了粤西山区大顶山小流域土壤侵蚀的时空变化及关键驱动机制。结果表明:大顶山小流域侵蚀模数为1948.1 t·km^(-2)·a^(-1),属于轻度侵蚀,但空间变异十分剧烈,变异系数为5.12,最大值可达191127 t·km^(-2)·a^(-1)。微度侵蚀(<500 t·km^(-2)·a^(-1))面积占流域总面积的80.6%,中度及以上侵蚀(>2500 t·km^(-2)·a^(-1))主要分布在植被覆盖度小于30%的桉树人工林幼林区,贡献了流域总侵蚀量的75.7%。2014—2019年间,大顶山小流域平均侵蚀年际变化不大,但土壤侵蚀空间分布变化较大,植被覆盖度、坡度和降雨是关键影响因素。桉树人工林种植导致自然植被破坏是引发造林区土壤侵蚀的首要原因。幼林区土壤侵蚀随坡度增加而显著增加,且极端降雨会使其加剧。随着桉树人工林林龄增长,土壤侵蚀又逐渐减少。该区土壤侵蚀关键部位为坡度大于25°的桉树人工林幼林区,土壤侵蚀治理关键期为造林后2~3年之内。本研究建议大于25°的陡坡区域应采用合理造林整地措施,同时避免破坏坡度大于35°区域的自然植被,并提高道路建设标准和加强林区管理,以应对极端降雨的挑战。

Unreasonable exploitation of artificial forest causes severe soil erosion in the mountainous areas of sou-thern China.The spatial-temporal variations of soil erosion in typical small watershed with artificial forest has signifi-cant implications for artificial forest exploitation and sustainable development of mountainous ecological environment.In this study,we used revised universal soil loss equation(RUSLE)and geographic information system(GIS)to evaluate the spatial and temporal variations of soil erosion and its key drivers of Dadingshan watershed in mountainous area of western Guangdong.The results showed that the erosion modulus was 1948.1 t·km^(-2)·a^(-1)(belonging to light erosion)in the Dadingshan watershed.However,the spatial variation of soil erosion was substantial,with variation coefficient of 5.12.The maximal soil erosion modulus was 191127 t·km^(-2)·a^(-1).Slight erosion(<500 t·km^(-2)·a^(-1))accounted for 80.6%of the total watershed area.The moderate erosion and above(>2500 t·km^(-2)·a^(-1))were mainly distributed in young Eucalyptus forest area with less than 30%of the vegetation coverage,which contributed nearly 75.7%of total soil erosion.During 2014-2019,the interannual variations of mean erosion of Dadingshan catchment was modest,but the spatial variation of soil erosion was large.Vegetation cover,slope,and rainfall were key drivers of such variation.The destruction of natural vegetation resulted by plantation exploitation was the primary cause of soil erosion in afforestation areas.Soil erosion significantly increased with the increases of slope gradient in the young forest area,which was aggravated by extreme rainfall.However,soil erosion gradually decreased with the increases of the age of Eucalypt plantation.Therefore,the hot spot of soil erosion was young forest areas of Eucalypt plantation with slope>25°,and the key period for soil erosion control was the first 2-3 years after Eucalyptus planting.We suggested that reasonable afforestation measures should be used in area with>25°slopes,and that the destruction of natural vegetation should be avoided on hillslope with>35°slope gradient.The road construction standards and forest management should be further improved to address the challenge of extreme rainfalls.