Vegetation and soil properties under different vegetation patterns along the slope in the hilly area of the Loess Plateau

Variation of plant community and soil property are a key index for vegetation restoration assessment. However,in the hilly area of the Loess Plateau,studies about variation of plant community and soil properties on slope scale under different vegetation patterns are limited.Therefore,in order to understand the effects of different vegetation patterns on plant community and soil properties during vegetation restoration,a case study was conducted in the hilly area of the Loess Plateau,located at the Yangjuangou catchment,Yan'an City,Shaanxi Province.In 2007,variation of plant community and soil physicochemical properties were measured under four types of slopes, each with different vegetation pattern,including Forest(forest planted by human),Grass,Grass - Forest - Grass (grass on the upper and lower slopes and forest on the middle slope),and Forest - Grass - Forest(forest on the upper and lower slopes and grass on the middle slope).On each of the four slopes,three transects were established from the hill tops to the hill toes.Sampling sites were spaced every 35-45 m along the transects.Each sampling site includes tree sample plots(one along each of the transects).In each sample site,one 10 m×10 m plot was used for tree survey;six 1 m×1 m plots were used for shrubbery and herbage survey.Soil samples(0 - 10 cm and 10 -20 cm) from each sample plot for each of the four slopes were analyzed for their physicochemical properties. The results indicate that the plant species under four vegetation patterns mostly belong to Compositae,Gramineae, Leguminosae and herbage species is much more than shrub.Jaccard similarity index which indicates similar degree between two plant community compositions shows the plant community composition under Forest and Grass was similar and the value was 0.56,and the Jaccard similarity index value between Grass - Forest - Grass and ForestGrass -Forest was 0.44.The Shannon Wiener diversity index of Grass was higher than the other three vegetation patterns.However,there were no significant differences among different vegetation patterns for Evenness and Simpson dominant indices.For soil properties,soil organic carbon and total nitrogen were significantly higher under Grass - Forest - Grass than under the other vegetation patterns and Grass had highest soil bulk density and soil water content compared to other vegetation patterns in 0 - 10 cm soil layer.In 10-20 cm soil layer,the soil properties variation was similar to 0 - 10 cm,soil organic carbon and total nitrogen was higher under Grass - ForestGrass, Grass had higher soil water content and lower pH value than the other vegetation patterns.In conclusion, compared to the plantation forest,the abandoned grass was better for plant diversity restoration,soil water reservation and soil pH melioration.Therefore,in the Loess Plateau whose water is a limited factor,land being abandoned was a better choice for vegetation restoration.However,if soil nutrients accumulation was considered in this area where the soil erosion is serious problem on the slope,Grass - Forest - Grass restoration pattern on the slope was better for soil carbon and nitrogen accumulation.Although significant difference was existed between different vegetation patterns,no significant relationship between plant diversity and soil nutrients variation.