Studies On Characters And Effect Of Soil And Water Conservation Of Different Vegetation Communities In Loess Plateau

This research aimed to understand changes of community characteristics in vegetation community in condition of Fencing enclosure,as well the differences of ecological functions between plantations and natural wild wood. Study plot was carried out in Xinyi town Lishi district located in west Shanxi province and different abandoned years farmland were selected with a method of a space series of replaced time courses.The community structure,species diversity, soil physical and chemical properties and soil erosion law of community successional series were studied systematically.The actual contents and conclusions mainly include the following several aspects:(1) Making research on abandoned farmland and finding:Deserted for 30 years in the natural state, sequencing based on abandoned years and result is Setaria viridis+ Bidens parviflora community deserted about 1～3a(B1), Artemisia community deserted about 5～11a(C2), Artemisia sacrorum+ Stipa bungeana community deserted about 10～15a(D3), Elymus dahuricus+ Lespedeza davurica+ Artemisia community deserted about 13～22a(E4), Hippophae rhamnoides community deserted about 24～30a(F5). During the entire course of desert,there are 43 kinds of herba??kinds of bush,and 55.81% of total species belong to Gramineae, Leguminosae and Compositae.This show that dominant families is very important in all vegetation communities. Shannon-Wiener index and Pielou's index increase in varying degrees,Simpson index decline accompany with abandoned years increasing.(2) In the entire sequence of abandoned farmland,soil bulk density ranges between 1.26 g/cm3 and 1.38 g/cm3, Soil total porosity increase from 51.76% in initial stage to 52.43% in last stage. Soil capillary presity and moisture content perform homogeneity in the whole process,have little relation with succession. Moreover,soil bulk density, total porosity and moisture content increase along with the depth of soil decreasing,but the change of soil capillary presity has little obvious relevance with soil depth. In relation to soil chemical properties,PH is change little, soil organic content in B1 attaching to initial stage is 7.52g/kg,and increase to 12.23g/kg in F5 in last stage.In addition,available P increase while soil TN and alkali-hydrolyzable nitrogen decline gradually.Other nutrients such like TP,TK and available K stabilize basically in the whole successional stage.Apart from TN and alkali-hydrolyzable nitrogen, surface convergence effect of other nutrients is not obvious among differernt vegetation communities.(3) Based on simulation rainfall in field,process of runoff and sediment yield in different vegetation communities is found.In the whole course, hydrographs of runoff and sediment yield in different sucessional stage fluctuate wildly.In the initial stage,sediment yield intensity and discharges are in high level. In Late stage ,however, sediment yield intensity and discharges are obviously reduced.And in same rainfall intensity,the sequence of average runoff yield intensity is A0(farmland)>D3>E4>C2>B1>F5,and the value ratio acoordingly is 3.72:2.98:1.53:1.425:1.36:1.05;the sequence of average sediment intensity is A0> D3> C2> F5> E4> B1and the value ratio correspondingly is 17.69:8.38: 2.94:1.57:1.06:1. The effect of sediment reduction of B1,C2,D3,E4,F5 respectively is 94.35%,83.41%,45.51%,91.02%,88.41% regarding to A0.The function of water and soil conserving of Hippophae rhamnoides community is best.The accumulation sediment makes a linear with rainfall duration, simultaneously form power function with rainfall intensity.The expression are y=ax+b and y=aIb respectively.(4) In this paper, ecological functions of natural forest and plantations are compared.And conclusions including:shrub layer of natural forest is more complicated than plantations while herb layer easier than planta??s. Besides, every soil physical property in natural forest is better than Pinus tabulaeformis plantation and locust tree plantation. To soil chemical properties,soil organic content and TN content in Populus davidiana natural fores are higher than relevant nutrient content in Pinus tabulaeformis plantation and locust tree plantation.And soil organic content in layer of 0-20cm of Populus davidiana is accordingly 1.17,4.56 times to Pinus tabulaeformis plantation and locust tree plantation.In addition, TN content in layer of 0-20cm of Populus davidiana is 6.88,3.95 times to Pinus tabulaeformis plantation and locust tree plantation.However,soil alkaline hydrolyze nitrogen content in Populus davidiana is low state and PH value is on the low side. There are same phenomenons about comparsion between runoff and sediment yield strength and cumulative runoff and sediment yield among three stands,that is locust tree plantation> Pinus tabulaeformis plantation>Populus davidiana.