| Forest site productivity evaluation is the basis of forest land management,which has important scientific value and practical significance for the rational use of existing forest land resources and the treatment or restoration of degraded soil.In this study,we analyzed 13 soil indexes including soil density,moisture content,nutrient content and microbial biomass in Larix principis-rupprechtii plantation in Taiyue Mountain,Shanxi Province.The site productivity of Larix principis-rupprechtii plantation was synthesized by the weighted additive index.To find out the main soil factors affecting stand productivity and realize the sustainable management of Larix principis-rupprechtii plantation,the correlation and stepwise regression analysis was used.The main conclusions were as follows:(1)Density regulation can effectively improve the soil condition of forest land.With the increase of density regulation intensity,the soil moisture content increased,while the soil density decreased.And moderate density regulation(1402 plants/hm~2)was conducive to the accumulation of soil nutrients and increased the content of soil microbial biomass.With the increase of stand age,soil moisture content,C,N,P and other nutrient contents of Larix principis-rupprechtii plantation decreased first and then increased,and microbial biomass content increased gradually.The soil physical properties and fertility of 50 year old stand were the best.The content of soil moisture,organic matter,total nitrogen,available potassium and microbial biomass in the mixed forest of Larix principis-rupprechtii and Betula platyphylla decreased gradually with the increase of forest age,while the contents of available N and P increased first and then decreased.With the deepening of soil layer,the contents of C,N and P decreased gradually,showing a certain surface aggregation effect.(2)Organic matter,moisture content and microbial biomass nitrogen constituted the minimum data set for site productivity evaluation of Larix principis-rupprechtii plantations.The results showed that the comprehensive evaluation index of Larix principis-rupprechtii plantations varied from 0.283 to 0.665.The order of SQI values of Larix principis-rupprechtii plantations with different density regulation intensity was as following:MT>HT>LT>CK,while the SQI values at different ages was in the order of 50a>30a>40a,and the SQI in the mixed forest of Larix principis-rupprechtii and Betula platyphylla was:H15a>H26a>H40a.On the whole,the site productivity of Larix principis-rupprechtii plantations in 50 year old stand was the best,and the SQI values of all stand types decreased gradually with the deepening of soil layer.(3)The increase of site productivity of Larix principis-rupprechtii plantation was helpful to increase stand productivity.Soil density and p H value were negatively correlated with stand productivity.Organic matter,total nitrogen,ammonium nitrogen,nitrate nitrogen and microbial biomass nitrogen were significantly positively correlated with stand productivity,while other soil factors had no significant effect on stand productivity.Stepwise regression analysis showed that soil nitrate nitrogen,ammonium nitrogen,soil density and microbial biomass nitrogen had great influence on stand productivity,and their contribution rates to stand productivity were 36.80%,13.07%,12.73%and 10.96%respectively,which were the main site productivity factors affecting stand productivity. |
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