Study On The Ecological Benefits Of Black Locust Plantation In Hilly And Gully Regions On Loess Plateau Of Semi-arid Area

In this paper the ecological benefits of Black Locust plantation in hilly and gully regions on loess plateau of semi-arid area with different ages and densities were taken as research object.The following factors and their interactions were studied. Including the growth status and the species diversity, the eco-hydrological function of canopy layer and litter layer, soil moisture-physical properties and the soil nutrient content. The purpose of this paper is provided evidences to the plantation management in this area, which has great significance in theory and practice.The study results show that:(1) In the same stand age(20a),the values of various growth indexes in higher density forest is lower than lower density forest, such as tree height,crown width and so on, but the value of canopy density is higher than lower density forest. The DBH (Diameter at Breast Height) of higher density forest is generally smaller, and the DBH increasing gradually with the decreasing of the forest density.(2) At the shrub layer and herb layer under different stand densities, as the stand density increasing the plant average height, vegetation coverage, biomass and the species richness were all decreasing. The undergrowth vegetations water content is higher in lower density than in higher density. At each stand densities community the Shannon-Weiner index, species evenness index and richness index of herb layer were all higher than shrub layer, but the dominance index of herb layer were lower than shrub layer.(3)With the rainfall precipitation outside forest increases, the precipitation under the canopies in each density forest increasing gradually. The density of the stands has great influences on the canopy density, the canopy density is higher in higher density,and during the same rainfall intensity the rate of canopy interception in higher density is bigger than lower density.The rainfall precipitation understory decreasing as the the stand density increasing.(4) With the stand density increasing the litter amount in different forest decreasing accordingly, and the per centum of undecomposed litter amount increasing gradually. The litter in medium-density (1 667strains/hm2) has better water holding capacity. With the passage of immersion time the water holding capacity of litter increased, and reaches the maximum after 24h.(5)With the stand density in is sparse, soil water content showed the trend of increasing at first and then decreasing, and for which the medium density (1 667 strains/hm~2) is the highest. For each stand density, soil water content in deeper layer will rise. And for each stand density, the soil bulk density increasing with soil layer deepening. Soil bulk density in the medium density (1 667 strains/hm~2) is smaller than other densities, it so that the action of soil-ripening in stand density is more strong. (6)Compared with the barren land, the soil total porosity of Robinia pseudoacacia woodland at different depths was increased, the soil total porosity of medium-density (planting spacing of 1.5×4m,1 667strains /hm~2) woodland is the biggest,up to 57.75%. Generally speaking the soil non-capillary porosity of higher densitie forest is larger than the lower densitie forest. Although the changes in soil nutrient content caused by the changes of density are not so obvious, the nutrient content and security fertility function of Robinia pseudoacacia forest is higher than grassland and agricultural land.