时间尺度对草地水土保持效应定量研究的影响

时间尺度效应的定量分析有利于进一步理解植被的水土保持机理。基于福建省长汀县河田镇草覆和裸土侵蚀试验小区2007—2010年的观测数据，分析了次降雨、月、季和年时间尺度下降雨、植被、保水和保土效应这4类参数的变化特征，并建立保水（土）效应RE（SE）的估算模型以探讨诸因素的联系，其中RE（SE）为草覆小区与裸土对照小区的径流深度（土壤流失量）的比值。结果表明:4类参数在各时间尺度呈现不同的量值及变化特性，RE和SE因消除了同类因子的影响在各时间尺度之间及其内部均相对稳定。在次降雨尺度RE较低（< 0.3）区间及月尺度下，降雨和植被的耦合作用导致了较好的保水效应，而在RE略高（0.3～0.4）和较高（> 0.7）区间以及年尺度，降雨因子主导了研究小区的保水效应（R² > 0.78）。从保土效应来看，在次降雨和年尺度主要受降雨或/和植被的影响，绿草叶面积指数能较好地表征研究小区草地的保土正效应（SE < 1，R² > 0.55），而最大30 min雨强可精确表征研究小区草地的保土负效应（SE > 1，R² > 0.79）。无论保水或保土效应，其估算模型在月和季两个中等时间尺度均存在较大的不确定性（R² ≈0.4）。可见在不同的时间尺度，影响草地水土保持效应的诸要素呈现不同的变化和耦合特征，显示时间尺度在植被水土保持研究中的重要性。

Influence of Time Scale on the Quantitative Study of Soil and Water Conservation in Grassland

Quantitative analysis of time scale effects on vegetation soil and water conservation favors further understanding the conservation mechanism. Based on the observation data of the grass covered soil and bare soil (control) experimental plots located in Hetian Town, Changting County of Fujian Province from 2007 to 2010, characteristics of 4 parameters(rainfall, vegetation, RE and SE) were analyzed at rainfall event, month, season, and annual scale, respectively, and then the linear regression models were established to describe the relationships between RE(SE) and its influencing factors of rainfall and vegetation. RE(SE) means the ratio of runoff depth (soil loss) of grass covered plot to that of the control plot. Results show that these 4 parameters presented different magnitude and variation at different time scales. RE and SE were relatively stable either within or among different time scales due to their ratios reducing the influence of other factors. The coupling of rainfall and vegetation led to better water conservation effect at lower REs (< 0.3) at rainfall event scale as well as at season scale, while the water conservation effect was dominated by rainfall at slightly higher(0.3~0.4)and higher(> 0.7)REs at rainfall event scale as well as at annual scale (R² > 0.78). For the soil conservation effect, rainfall or/and vegetation were the dominated influence factors at rainfall event and annual scales, and the grass LAI could basically present the positive conservation effect(SE < 1, R² > 0.55), while the maximum 30 min intensity (I₃₀) could describe the negative conservation effect more accurately(SE > 1, R² > 0.79). More uncertainties(R² ≈0.4) exist in the models of both RE and SE at two moderate time scales (month and season). Consequently, factors influencing soil and water conservation effect of grass present different variation and coupling characteristics at different time scales, indicating the importance of time scale in terms of the study on soil and water conservation.