| In order to perfectly implement ecological environment rehabilitation & vegetation restoration and the returning farmland to forest engineering in semiarid loess hilly and gully area, by learning the effects of soil and water conservation of various vegetation types/land use and theirs influences on local soil moisture, the study was made on the effects of runoff and soil erosion reduction of typical vegetation types including slope cropland, pastureland, natural grassland, woodland and shrubland over a period of 14 years from 1986 to 1999 under the natural rainfall condition and the soil moisture dynamics of the depth 0-100 cm of hillslope and gully slope in 2002 in Anjiagou catchment, Anding district, Dingxi city. The results indicated: ①In 14 years, the runoff and soil erosion occurrence times had little difference in different gradient plot but had obvious difference in various vegetation, and their occurrence sequence was cropland > pastureland > woodland > natural grassland > shrubland;②The mean annual amount of runoff and soil erosion had remarkable difference in various vegetation in 14 years and their sequence was cropland > pastureland > woodland > natural grassland > shrubland. The rainfall intensity and vegetation type were main two factors of soil erosion occurrence and the erosion was rapidly increasing with the enhancing of rainfall intensity under the same slope degree;③The occurrence of runoff and soil erosion of various vegetation characterized with different distribution in the observation mouth from April to September. Among them, July and August had more runoff andsoil erosion, but less in May and September and theirs reduction effects also distributed in July and August;d)The accumulation amount of runoff and soil erosion of various vegetation was increasing with the prolong of the year in 14 years after the vegetation grown, and the amount of cropland was highest, the second were pastureland and woodland, and the lest were shrubland and natural grassland;?The different temporal changes of runoff and soil erosion reduction rate of various vegetation represented similar characteristics, namely the runoff and soil erosion reduction rate of shrubland was continuously improving and maintained higher level, the that of natural grassland was increasing in early years and then decreasing in late years and also maintained higher level, the two one represented high effective and more sustainable effects and their soil & water conservation effect was best;whereas the that of pastureland was rapidly decreasing with the prolong of years and maintained lower level, but woodland was rapidly decreasing in runoff reduction rate and steadily increasing in soil erosion reduction rate and also maintained lower level, the soil and water conservation effect of two one was worse and less sustainable;the that of cropland was worst;?The seasonal changes of soil moisture of hillslope and gully slope with depth 0-100 cm had similar characteristics, namely the changes of soil moisture went through the course of increase -decrease - re-increase - re-decrease and the general changing trend was declining, and its changing curve was double peak type. The soil moisture is higher in May but was lower in July. But there were some differences in soilmoisture seasonal changes between hillslope and gully slope, namely it was more obvious in hillslope and its soil moisture differences in various vegetation enhanced in humid season, but was less obvious in gully slope and its differences enhanced in arid season;(§)The section changes of soil moisture of hillslope and gully slope were hardly obvious in comparison with seasonal changes and the changing curve was smooth. Its general changing trend is that the soil moisture of hillslope was decreasing with the increment of soil depth, whereas increasing in gully slope. The moisture changes was great in the soil depth of 0~60 cm, where it was more rapid in hillslope decreasing and gully slope increasing, but was slight in the depth of 60~100 cm;?The vegetation types and slope aspect had great influences on soil moisture, but slope position was slight. In terms of slope aspect, the soil moisture of north slope was obviously higher than that of south slope. At the same aspect, the soil moisture of grassland was higher than that of shrubland;?The gully soil moisture condition was better than that of hillslope and could meet the water requirement of all kinds of vegetation in arid season. The wind speed and atmospheric radiation of gully slope were lower than that of hillslope, but atmospheric temperature and humidity were higher than that of hillslope. |
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