USLE/RUSLE模型中植被因子变化特征及其影响因素

植被因子是USLE/RUSLE模型中最重要的影响因子,其数值变化特征及其影响因素广受关注。以广东省五华县源坑水小流域2011—2013年的径流小区次降雨水沙观测数据为基础,分析了径流小区C值在不同时间尺度的变化特征及其受降雨、植被类型的影响。研究表明:(1)不同时段间C值存在一定波动,其中旱季的C值均大于雨季,夏秋两季的C值较大,且较为接近。各径流小区的C值普遍存在11、8、7月较大,6、5、1月较小的现象,且草本植物C值受植被覆盖度影响较大。(2)降雨量与径流小区C值呈正相关关系,桉树、松树、糖蜜草径流小区C值与次降雨量、各降雨量区间平均值的相关系数分别为0.360**、0.349**、0.291**,0.912*、0.909*、0.822,相较于草本植物,木本植物的C值受降雨影响更大,仅以植被盖度衡量C值有待商榷。(3)相较裸土小区,桉树、松树、糖蜜草小区2011—2013年的土壤流失减幅分别为14.2%、21.5%、23.2%,其C值分别为0.814、0.748、0.772,3种植物中糖蜜草与松树均具有相对较好的水保效益,桉树的水保效益稍逊。

Variations in vegetation cover factors and their influence on USLE and RUSLE

Vegetation factors are the most important influences on USLE/RUSLE models. The observed data for runoff and sediment yields from field runoff plots between 2011 and 2013, their variation characteristics, and the impacts of rainfall and vegetation types on the C values were analyzed for different time scales. The results showed that: (1) The C values fluctuated between seasons. The values were higher for summer and the fall than for spring and winter, and were similar for summer and fall. Furthermore, dry seasons show higher C values than wet seasons. Specifically, higher values were found in November, August, and July, and lower values were observed in June, May, and January. The C values for herbs were significantly affected by the vegetation coverage. (2) The C values were positively correlated with rainfall volume, and the correlation coefficients between the C values and rainfall volume for individual rainfall events were 0.360^{* *}, 0.349^{* *}, and 0.291^{* *} for the eucalyptus and pine trees, and Melinis minutiflora runoff plots, respectively. The correlation coefficients for average interval rainfall volume and the C values were 0.912^*, 0.909^*, and 0.822 for the eucalyptus and pine trees, and Melinis minutiflora runoff plots, respectively. The rainfall volume had a much stronger influence on the C values for the woody plants compared with the herbaceous plants, suggested that the C values could not be determined by the vegetation coverage alone. (3) A comparison of the runoff plots for bare soil showed that the volume of soil lost was reduced by 14.2%, 21.5%, and 23.2%, and the C values were 0.814, 0.748, and 0.772 for the eucalyptus and pine trees, and Melinis minutiflora runoff plots, respectively. The results showed that Melinis minutiflora and pine trees were better at conserving soil and water than eucalyptus.