Characters Of Different Vegetation Communities In The Water-wind Erosion Crisscross Region Of Northern Loess Plateau

The water-wind erosion crisscross region of Northern Loess Plateau is one of the most vulnerable areas where the vegetation destructed and soil eroded. By the projects of conversion of cropland to forest or grassland and ecological restoration, the development of vegetation in this area has gone into a new period and the characteristics of the vegetation communities have changed. Knowing the characteristics of the vegetation communities and analyzing the correlation between the physical and chemical properties of the soil in this area will play an important role in commenting on the merits and demerits of the various vegetation recovery models and building efficient soil and water conservation vegetation.We adopted Quadrat method to investigate the ecological characteristics of different communities.And Harvest method was adopted to test the biomass of undergrowth. The hydro-physical property of soil were tested by referring the National standard of P.L.A (GB7837-87) and drying method.The Chemical Properties of soil were tested by Conventional methods of the lab.On the basis of researching the characteristics of communities,we got some results as follows:(1) There were 39 herb species in grassland plots which belonged to 27 generas,14 families.Meanwhile there had 47 Herb Species in forest or shurb plots which belonged to 36 generas,14 families.The Compositae had the most Herb Species, and than the Gramineae,Leguminosae,Rosaceae. The biomass of undergrowth vegetation was Chinese pine(new plantation)> Prunus armeniaca> Simon polar+Prunus armeniaca> Chinese pine+Simon polar+Prunus armeniaca> Heibei polar> Sea Buckthorn> Heibei polar-Sea Buckthorn> Chinese pine.LAI was Chinese pine> Sea Buckthorn> Heibei polar-Sea Buckthorn> Simon polar+Prunus armeniaca> Chinese pine+Simon polar+Prunus armeniaca> Heibei polar> Prunus armeniaca> Chinese pine (new plantation).The coverage of undergrowth vegetation was:Chinese pine (new plantation)> Prunus armeniaca> Simon polar+Prunus armeniaca> Chinese pine+Simon polar+Prunus armeniaca> Heibei polar> Sea Buckthorn> Heibei polar-Sea Buckthorn> Chinese pine.(2)The vertical structure of forest communities was simple, usually less than 2 layers. Most of the communities only had single tree layer or shrub layer. The biodiversity of natural secondary forests was more abundant than that of plantations. The stability of undergrowth vegetation of different forest communities was:Chinese pine+Simon polar+Prunus armeniaca> Chinese pine (new plantation)> Prunus armeniaca> Heibei polar-Sea Buckthorn> Heibei polar> Sea Buckthorn> Simon polar+Prunus armeniaca, the tree communities> Shurb communities, communities with complicated vertical structures> communities with simple vertical structure(3)The moisture contents of forest community is greater than that in the grass, and that in the natural secondary forest is over that in the plantation. Heibei polar and Heibei polar-sea buckthorn have the greatest moisture contents.In the grass communities, capillata Linn. community and vestita Wall. ex Bess. community have more greater moisture contents. At the vertical direction of soil,the moisture contents of the surface layer (0-20cm) is less than that in the sub-surface layer (0-40cm). Generally, the water-holding capacity of forest communist is over that of the grass community. The available N is 95.9g/kg to 230.2 g/kg, and the order is forest community>shrub-grass community>herbage community.The content of available P which is 4.74 g/kg to 19.02 g/kg is the lowest.The available K is great.The content of soil organic matter is 1.98g/kg to 22.77g/kg.Among these,the greast amount is the surface layer of the Simon polar+Prunus armeniaca community, and the least is the sub-surface layer of the secalinus (Georgi) Tzvel.+Edible alfalfa community (20-40cm). the character of the soil infiltration,community Characteristics,the porosity of soil non-capillary tube,organic continent.ect have a great pertinence. The simulate of different community infiltration measured value and A.H.Kositiakov model have a good fitting degree.plant cover degree,leaf area index, species enrichment degree,plant diversity, herbage biomass and soil moisture contents, infiltration rate, rapidly available nutrient,organic matter have a correlation relationship.(4) Structure of herb communities in the natural restoration area and artificial area restoration which are based on small watershed scale is similar, and the similarity coefficient is 0.925. On the community stability and accumulation of organic, the natural restoration area and artificial restoration area have their own advantages and disadvantages. The later has its advantage about the biodiversity and community stability of recent one decade, and the former has advantage about biomass accumulation and water conservation.