Effects of vegetation structure types and rainfall patterns on soil and water loss of understory vegetation in red soil areas of South China
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Abstract
Vegetation and rainfall are the key factors that affect the soil and soil erosion. Exploring the surface runoff and soil loss process associated with different rainfall patterns and vegetation structure types is of great significance to the development of soil and water conservation. In this study, we carried out a series of experiments on surface runoffs and sediments monitoring at different runoff plots with five structures types of vegetation (i.e., shrub-grass mixed forest, grassland, low shrub, arbor forest, high shrub). There are 8 runoff test plots with length × width (10 m×2.6 m) on the gentle slope of 8°in Red soil Ecological Experimental Station, Yingtan city. The experiment lasted three years from 2016 to 2018. During the study period, 93 individual natural erosive rainfall events, surface runoffs and sediments data were collected, as well as the vegetation structure parameters were obtained. The self-organizing mapping (SOM) method was applied to classify rainfall patterns according to rainfall characteristic indicators such as rainfall amounts, rainfall durations, 60min maximum rainfall intensity, average rainfall intensity and rainfall amount concentration index. Then the characteristics of soil and water loss under different rainfall patterns and vegetation structure types were studied, and the effect of rainfall and vegetation on soil and water loss were quantitative analysis by redundancy analysis (RDA). The results showed that SOM method could identify the four typical erosion rainfall patterns in red soil region, the rainfall patterns were as follows: RI (low intensity, long duration, minor amount of rainfall and low rainfall concentration index), RII (medium amount of rainfall, moderate intensity and long duration), RIII (short duration, strong rainfall intensity and high rainfall concentration index), RIV (a great amount of rainfall, strong rainfall intensity and long duration). Among all of the erosion rainfall events, the least rainfall was pattern RIV, which was the most erosive and destructive, so it was easy to cause serious soil erosion. RIII was the main pattern that made the highest cumulative contribution rate to soil and water loss. The erosion ability of pattern RII was moderate, but it was also easy to cause soil and water loss due to its moderate intensity and long duration. The pattern RI could hardly cause soil erosion. Vegetation structure types significantly affected the soil erosion and runoff generation, and the soil and water conservation function of different vegetation in turn was as followed the order of shrub-grass mixed forest, grassland, low shrub, arbor forest, and high shrub. RDA results shown that comprehensive interaction effects on soil erosion exist between rainfall patterns and vegetation structure types. The ability of soil and water conservation of vegetation decreased gradually and the effects of rainfall became greater in the later stage of erosion process, when rainfall patterns changed from weak to strong (RI?RII?RIII?RIV), meanwhile the dominant factors of soil and water loss changed from vegetation to the interaction of vegetation and precipitation, and then to rainfalls. The influences of canopy structure on soil and water loss reduced, while the ones of rainfall increased when vegetation structure types changed from near surface vegetation to shrub and tree.
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