The Biodiversity And Soil Hydrology Character Of Different Plant Communities In Loess And Bedrock Area

The irrational utilization of land has resulted in a series of ecological problems. Reducing cultivated land to plant forest, adjusting land use structure and restoring vegetation have been needed urgently to improve the ecological environment of the loess hilly and gully region.The problems of vegetation construction structure allocation and low-yield forest modification measure rationality are researched in loess and bedrock area ecotone,in order to offer references for the choice of proper plant community types and allocation in the course of vegetation construction.The diversity structure character and soil hydrology function of plant communities after conversion of cropland to forest project in loess and bedrock area ecotone was researched by using restoration ecology,forest hydrology,forest management principles and method.Specific conclusions are as following:1.The structure character during plant communities succession in loess and bedrock area ecotone was studied(1)During the progressive succession process of the community, the changes of community dominant species from heliophilous plant to heliophobous plant.The structure of community dominant species have great changes during the progressive succession process of the community,the change characterisitics are as follows , herb layer : Artemisia annua, Eriophorum comosum→Artemisia capillaris→Eriophorum comosum, Polygonatum odoratum, Thalictrum aquilegifolium. var. sibiricum→Eriophorum comosum→Eriophorum comosum, Viola verecunda, shrub layer : Larix principis-rupprechtii Mayr→Quercus wutaishanica, Spiraea salicifolia→Cotoneaster zabelii:tree layer:Larix principis-rupprechtii Mayr→Betula platyphylla→Betula platyphylla,Quercus wutaishanica,Acer truncatum.The structure characterisitics of the three living form showed during the progressive succession process of the community, the changes of community dominant species from heliophilous plant to heliophobous plant.(2)The different living forms diversities change trend in different successional stages are difference.The changing tendency of diversity indices, evenness indices and richness index in tree layer and shrub layer are similar,all gradually raise during the progressive succession process of the communities.But the changing tendency of diversity indices, evenness indices and richness index in herb layer was gradually decreased,it showed herb layer status was gradually weaked.(3)The leading factors of community succession diversity as follow:one is diversity—evenness factor,another is richness factor.The result of biodiversity indices principal component analysis show that there was an obvious positive correlation between the first principal component and diversity indices ( Simpson index,Shannon-Wiener indices and Peilou,Alatalo indices );the second principal component and richness index have an obvious positive correlation.So the leading factors of community succession diversity as follow:one is diversity—evenness factor,another is richness factor.2. The soil hydrology character during plant communities succession in loess and bedrock area ecotone was clarified.(1)During the progressive succession process of the communities, soil density gradually decreased. The soil density gradually decreased during the progressive succession process of the communities. Mixed coniferous and broad-leaved forest and broadleaved mixed forest stage forest land soil density are clearly little than other succession stages.(2)During the progressive succession process of the community, the forest land soil porosity has obvious improvement and water conservation function was enhanced.The comparison analysis for soil water storage of the experimental samples in 0-40cm of every succession stage showed that, soil porosity percentage and water storage of each stage was bigger than succession stageⅠin the procession of progressive succession, in which adsorption and retention water storage were increased. It was indicated that the structure of forest ecosystem optimized constantly as the plant community was in retrorse succession, as the stand composition became complicated, species richness and diversity index increased, the function to improve soil structure strengthened, thus made high improvement of the soil pore space status and water storage capacity, leading to significant improvement of water storage ability and water conservation function of the stand soil.(3)The progressive succession process of the plant communities favorable to soil water infiltration and reduce surface runoff flow.The effect of plant community on improving soil infiltration capability was stronger as the succession stage tended to be climax community, and the effect of complicated community was higher than simple one.The variance analysis and multiple comparative test were done for the soil early and steady permeability rate of each succession stage in the procession. The results showed that, as to the early permeability rate, the succession stageⅠandⅡhad significant differences with the stage ofⅤandⅥ; as to the steady permeability rate, the difference between stages was significant. It was indicated that difference of infiltration rate between stages was significant.Fitting results for different plant community in the process of soil infiltration by four kinds of infiltration model showed that, Horton model reflected the soil infiltration process better than others, and was suitable for descript the soil infiltration characteristics in the process of plant community succession of this research area. However, the fitted steady permeability rate by the model of Philip,Kostiakov and the Common experienced infiltration model showed great deviation from the actual value.(4)Forestry ecological engineering, as conversion of cropland to forest project, have accelerateed the progressive succession process of the community.The application of forestry ecological engineering in the program areas , like the protection of natural secondary forest and conversion of cropland to forest and grassland, promoted the progressive succession process of the plant community and made the community succeed to the direction favorable to the environment improvement, as well as made the structure of the plant community tend to be optimized and the hydrological characteristics of forest soil develop to be good.The relationship between structure and hydrological function of the plant community is closed, as changes of the soil hydrological characteristics in different succession showed a same trend with structure change of the vegetation. Correlation analysis showed that hydrological function had significant correlation with species abundance of the community, the higher the abundance was, the stronger the function was, which indicated species abundance of the community was an important index to reflect degradation or recovery of the ecosystem structure.3. Modification measures applied to Larix principis-rupprechtii Mayr low-yield forest were confirmed in loess and bedrock area ecotone.( 1 ) Different modification measures have an obvious effects on Larix principis-rupprechtii Mayr growth process.Four transformation measures, felling with 50% thinning intensity, felling with 50% thinning intensity, removal shrubby undergrowth, enclosed protection, which had significant effects in tree height, breast diameter, and individual volume growth, were taken to reconstruct larch stands in reconstruction areas of low yield and efficient forest.( 2 ) Different modification measures have different effects on Larix principis-rupprechtii Mayr DBH (diameter at breast height)distribution characteristics.Tree numbers of stands with four tending measures had great differences on diameter grade distribution curve. The diameter and density structure of B stands with 30% thinning intensity significantly better than other three ones. The summit of the diameter distribution curve of A stands with 50% thinning intensity greatly declined to the right side, which showed that thinning intensity was too much to make a lower utilization rate of the woodland resources. The summit of the diameter distribution curve of C stands with enclosed protection and D stands with removal shrubby undergrowth declined to the left side, which showed a high stand density, leading to too many small diameter timbers that did not conform practical production.The diameter distribution of B stand conformed to normal school with 8.25cm average diameter whose diameter and density structure was reasonable and its thinning intensity can be taken as reference standard in reconstruction areas of larch stands in low yield and efficient .( 3 ) The suitable modification density is 2450 plants?hm-2 for Larix principis-rupprechtii Mayr low-yield forest.Under site environment of the research area, the optimum time to reconstruct larch stands in low yield and efficient is when they are 10-12 years old, the suitable density is about 2450 plants per hectare, which can be initial planting density(with 2.0×2.0m or1.5×2.5m planting space) in artificial afforestation without considering harvesting and utilization in earlier stages.