The Characteristics Of Habitat Succession And Its Evaluation Of Different Vegetations In Datong County

This paper takes the converted farmland (Picea crassifolia community and Betula platyphylla community) in Datong mountains Qinghai province as the study object, through field investigation, observation on the spot and lab analysis, from aspects such as biodiversity, vegetation productivity, soil physical and chemical property, hydrological effect and so on, to comparatively research the succession characteristics of the habits of the converted farmland in Datong mountains, for the first time using the principal component analysis (PCA) method to comprehensive evaluate the habit qualities of Datong mountains, in order to offer scientific basis for the vegetation reconstruction and ecology restoration of converted mountain. The main result shows as following:(1) Changes of biodiversity. With the increase of artificial forest age in converted farmland, the forest canopy density is increasing and the number of herb species is reducing, the diversity is gradually near to that of natural forest (1.5318). Each vegetation community type in different succession phase is always similar to that in neighboring succession phase, and the changing extent of similarity coefficient of herb layer is more lager than that of the whole community, the similarity coefficient of whole community is more than that of herb layer. The relationship between species integrated diversity and species diversity of herb layer is according with positive correlation. The order of richness indexes (R₀) of Picea crassifolia communities with different converted years is: artificial forest with 14 years (26) > artificial forest with 19 years (12) > artificial forest with 27 years (10), and the order of Shannon-Wiener indexes (H) is the same, artificial forest with 14 years (2.5598) > artificial forest with 19 years (1.9491) > artificial forest with 27 years (1.7449). The orders of Betula platyphylla communities are similar to those of Picea crassifolia communities.(2) Changes of biomass from the forest with 10 years to forest with 50 years. The community biomass is getting more with the increase of forest age, the relationship between biomass and converted years is according with significantly positive correlation. Arbor layer takes main advantage in the community, the changing trend of biomass of arbor layer is the same with that of whole community, the similarity coefficient is 0.999, reach extremely remarkable level with α =0.01. The biomass of herb layer is reducing and the thickness of litter is increasing. The changing trend of community productivity is the same with biomass.(3) Succession of soil physical property. The soil porosity and moisture content of Picea crassifolia community and Picea crassifolia community are increasing with the increase of converted years, and on the whole present a growth trend. Aggregate content with diameter less than 5mm takes advantage in different soil layers of converted farmland, soil structure is improving, performing a changing rule of the indexes of aggregate degree, aggregate condition,structural grain are ascending, while the changing rule of indexes of distribution ratio,distribution coefficient are opposite, and the changing extent of subsurface is relatively stable. The changing rules of soil bulk density are different in different layers, in the surface (0-20cm) the soil bulk density increases first and then decreases and at last gradually tends to be stable, while in the subsurface (20-40cm) the soil bulk density decreases first and then increases and at last gradually tend to be stable.(4) Succession of soil chemical property. After converting farmland to forest, with the vegetation succession, the organic content is gradually increasing and the increasing extent of surface lay (0-20cm) is the largest, at the beginning of the converted farmland the average organic content is 2.596%, and average content of Picea crassifolia forest with 55 years is 7.745%, Betula platyphylla forest with 50 years is 7.513%, 2.98 times and 2.89 times of the earliest average respectively. The changing rules of the contents of total N, available N, available P and available K, CEC are the same with organic content, presenting an increasing trend in the whole. Picea crassifolia forest with 14 years begins to enter a fast-growing period, absorbs more nutrients from the soil in order to meet the need for growing, so the organic content of Picea crassifolia forest with 19 years is less than that of 14 years. After that as the tree growth speed is getting faster, the biomass is increasing and the organic matter come back to soil is increasing too, so the organic content presents a steadily accumulating state. Total K content is generally stable, soil pH value is decreasing and soil anti-scourability is gradually increasing.(5) Study on hydrological effect shows, rainfall interception amount of the three canopies and water holding capacity of litter are increasing with the increase of converted years. The relationships between the water-keeping capacity of litter and the thickness of litter layer, accumulation of litter, converted year, biomass are according with significant correlation. The relationship between the soil infiltration rate and the converted year is according with power function correlation. The soil initial infiltration rate is increasing with the increase of forest age, both initial infiltration rate and stable infiltration rate are gradually close to those of natural forest.(6) For the first time using the principal component analysis (PCA) method to comprehensive evaluate the habit quality of Datong mountains, the result shows: with the increase of converted year, the comprehensive evaluated value of habitat quality is generally tend to be increasing, nature forest with 55 years (0.287) > artificial forest with 27 years (-0.17755) > artificial forest with 19 years (-0.29585). As a whole, because of the mass consumption of nutrients during the fast-growing period, comprehensive evaluated value of the artificial forest with 19 years and 27 years are both lower than that of 14 years (0.09245).