Effect of Vegetation and Precipitation upon Runoff and Sediment Production on Slope Lands of the Loess Area in China

According to fixed-position data for 1992-2003 from 16 runoff plots of Caijiachuan watershed which lie in Jixian County, Shanxi Province, in the loess area, this paper studied the relationship between vegetation and runoff and sedimentproduction on slope lands. The results showed as follows: 1) Runoffand sediment production in Robinia pseudoacacia forestand Pinus tabulaeformis forest had a high correlation with precipitation amount and rainfall intensity, but the correlation decreased gradually with the increase of canopy density; 2) The secondary forest had better function of soil and water conservation than artificial R. pseudoacacia forest, and runoff and sedimentproduction in the former in an individual rain event was 65%-82% and 23%-92% lower than thosein the latter, respectively;3) The difference ofrunoff and sediment production in several land uses was very distinct. Runoff and sediment production in Ostryopsisdavidiana forest and the secondary forest were the least; runoff and sediment production in artificial R. pseudoacacia forest and P. tabulaeformis forest were 5-fold as much as those in O. davidiana forest. Besides, runoff and sediment production in mixed stand of apple trees and cropswere 16.14-fold and 2.96-fold higher than that in O. davidiana forest, respectively, but theamount decreased obviously after high-standard soil preparation for theformer;4) Based on gray correlation analysis of variousfactorsaffecting runoffand sedimentproduction on slope lands, it can be seen that stand canopy density and herb and litter biomass werethe most significant ones, whosegray correlation valuesall exceeded 0.6. Therefore, mixed forest with multi-layer stand structure and shrub forest should be developed in vegetation reconstruction of the loess area, which help to increase coverage and litter thicknessto cut down the runoffand sediment production dramatically on slope lands.

Combining gradual and abrupt analysis to detect variation of vegetation greenness on the loess areas of China

The annual peak growth and trend shift of vegetation are critical in characterizing the carbon sequestration capacity of ecosystems.As the well-known area with the fastest vegetation growth in the world,the Loess Plateau(LP)lands find an enhanced greening trend in the annual and growing-season.However,the spatiotemporal dynamics of vegetation peak growth and breakpoints characteristics on time series still needs to be explored.Here,we performed tendency analysis to characterize recent variations in annual peak vegetation growth through a satellite-derived vegetation index(NDVI_(max),Maximum Normalized Difference Vegetation Index)and then applied breakpoint analysis to capture abrupt points on the time series.The results demonstrated that the vegetation peak trend had been significantly increasing,with a growth rate at 0.68×10^(-2)·a^(-1) during 2001-2018,and most pixels(70.81%)have a positive linear greening trend over the entire LP.In addition,about 83%of the breakpoint type on the monthly NDVI time series is a monotonic increase at the pixel level,and most pixels(57%)have detected breakpoints after 2010.Our results also showed that the growth rate accelerates in the northwest and decelerates in the southeast after the breakpoint.This study indicates that combining abrupt analysis with gradual analysis can describe vegetation dynamics more effectively and comprehensively.The findings highlighted the importance of breakpoint analysis for monitor timing and shift using time series satellite data at a regional scale,which may help stakeholders to make reasonable and effective ecosystem management policies.

Structure and governance model of rural social space quality:A case study of Longxi County in the Loess Hilly Area of China

The rural social space quality is an important indicator to measure the living standard and thinking ideas and so forth of rural residents in a certain region.In this paper,213 administrative villages in Longxi County of the Loess Hilly Area,China are taken as evaluation units to construct the evaluation model of the rural social space quality.This paper deeply analyzed the variation patterns and their formation mechanism of the rural social space quality at a village scale,and proposed a governance model based on the rural social space quality.The results show that:(1)the social space quality levels of individual administrative villages show a gradually decreasing trend from the township seats to outward.The eastern part of Longxi County has a relatively high education level and living standard,and the western part has a relatively high population stability level and income level.(2)The rural social space quality is mainly in a ring structure,supplemented by the interlaced structure.The core area is the towns and their surrounding areas,while the transition area,marginal area,and other areas are expanded around the core area.(3)Social forces and spatial effects jointly shape the variation of the rural social space quality.Social organizations provide a driving force for the allocation of elements,and interweaving with the spatial effects lead to the differences in the social space quality.(4)The governance models of the rural social space quality are constructed based on the principles of retaining the rural“people”,optimizing the rural“land”,and developing the rural“industry”,so as to improve the rural centripetal force,core force,inner thrust,and source power.

Hydrological cycle research by D&^(18)O tracing in small watershed in the loess hilly region

The objective of this study was to determine the mechanisms of the hydrologic cycle in the loess area in China.Sixty eight water samples from precipitation,soil water of the 0-4 m layer,surface water in the valley,ground water(spring and well)were collected and the Deuterium(D)and Oxygen-18(^(18)O)of these water samples were analyzed to interpret the relationship among those waters in the watershed in the loess hilly region during 2005-2009.The results show that:the D&^(18)O of precipitation in Yangou was consistent with that of Xi,an,apparently the north migration of water vapor in Xi^an;according to the correlations among the differential waters in D&^(18)O,confirmed that precipitation recharge could account for most of the sources of valley flow,with part of the recharge water going to soil water recharge.The D&^(18)O of groundwater were very close to that of precipitation,likely the soil preferential flow was dominant in groundwater recharge although the infiltration had a certain lag.Under the influence of rainfall and evaporation,the response of the soil moisture profile,and its D&^(18)O profile were different.The soil moisture had the strong influenced layer in the 60-160 cm range,a weak impacted layer in 60 l60 cm,and a stable layer below l60 cm.It was shown that the soil evaporation depth could be up to l60 cm because the D&^(18)O changed in that depth.The study could increase our understanding of the magnitude and pattern of the hydrologic cycle,which should improve water resources management in the watershed scale.