| In this paper,46 sample plots of Chinese fir plantation with similar site conditions are selected as the monitoring sample plots,including 8 plots arranged in 2009,12 plots arranged in 2010 and 26 plots arranged in 2011,for tending thinning.The growth characteristics of Chinese fir plantation before and after tending thinning were investigated,the soil nutrient indicators(organic matter,total nitrogen,total phosphorus,total potassium,available phosphorus and available potassium)were determined,the growth characteristics of Chinese fir plantation were studied,the effects of tending thinning intensity and tending thinning time on soil nutrients of Chinese fir plantation as well as the effects of tending thinning on soil nutrients of Chinese fir plantation of different ages were explored,and the response of soil nutrients of Chinese fir plantation to tending thinning was further analyzed.The main conclusions are as follows:(1)Compared with the Chinese fir without tending thinning,the average increment of DBH,tree height,volume,biomass and carbon storage of young Chinese fir stands with tending thinning was17.00%,4.03%,24.62%,24.37%and 25.11%respectively;that of middle-aged stands was 9.18%,8.99%,21.75%,29.62%and 34.00%respectively;and that of aged stands was 15.56%,19.23%,9.15%,7.78%and 9.37%respectively.(2)The different tending thinning intensity had significant effect on the content of soil nutrients(organic matter,total nitrogen,total phosphorus,available phosphorus and available potassium)of Chinese fir plantation(P<0.05),but had no significant effect on the content of total potassium.The contents of organic matter,total nitrogen,total phosphorus,total potassium,available phosphorus and available potassium in tending thinning ? were 14.30g/kg,1.58g/kg,46.37g/kg,1,89g/kg,2.59mg/kg and 163.29mg/kg respectively,while the soil nutrient content of the sample plots without tending thinning was generally low.Compared with the sample plots without tending thinning,the soil nutrient content of thinning ? increased 66.39%,20.31%,36.02%,14.06%,60.32%and 32.72%respectively.(3)With the increase of tending thinning intensity of Chinese fir plantation,the comprehensive score of soil nutrients in Chinese fir plantation increased first and then decreased.Among them,the highest comprehensive score of soil organic matter in thinning ? was 1.1735,followed by that in thinning ? which was 0.5570;that in thinning ? was 0.016,and that in uncultivated thinning ? was the lowest,only-0.5768.The comprehensive scores were sequenced as thinning ?(26%-35%)>thinning 1(10%-25%)>thinning ?(36%?50%)>CK(0%)(4)The different thinning time had significant effect on the content of soil nutrients(organic matter,total nitrogen,total phosphorus,total potassium and available potassium)in Chinese fir plantation(P<0.05),but had no significant effect on the content of available phosphorus.Among them,the contents of soil organic matter,total nitrogen,total phosphorus and available potassium were the highest in 6 years after tending thinning,which were 12.71g/kg,1.55g/kg,44.00g/kg and 166.03g/kg respectively,36.63%,24.84%,26.71%and 28.57%respectively higher than those in 6 years without tending thinning;the contents of total potassium and available phosphorus were the highest in 7 years after tending thinning,which were 1.98g/kg and 2.32mg/kg,20.47%and 61.62%higher than those in 7 years without tending thinning.(5)The comprehensive score of soil nutrients of Chinese fir plantation in the sample plots after tending thinning was significantly higher than that in the sample plots without tending thinning.With the decrease of tending thinning time of Chinese fir plantation,the comprehensive score of soil nutrients of Chinese fir plantation increased first and then decreased.Among them,the comprehensive score of soil nutrients in 6 years after thinning was the highest,which was 0.6775,followed by that in 5 years after thinning,which was 0.5588;that of 7 years after thinning was the lowest,which was 0.4835.The comprehensive scores were sequenced as 6 years after thinning>5 years after thinning>7 years after thinning.Among the sample plots without tending thinning,the comprehensive score of soil nutrients in 6 years without tending thinning was the highest,which was-0.3627,followed by that in 5 years without tending thinning which was-0.6048,and that in 7 years without tending thinning was the lowest which was-0.8068.(6)The different ages had significant effect on the contents of soil nutrients(organic matter,total phosphorus,available phosphorus and available potassium)in Chinese fir plantation,but had no significant difference in the contents of total nitrogen and total potassium.Among them,the contents of soil organic matter,total potassium and available phosphorus of young stands were the highest,which were 12.75g/kg,1.91g/kg and 2.86mg/kg respectively,36.06%,27.20%and 50.85%higher than those of young stands without tending thinning;and the contents of total nitrogen,total phosphorus and available potassium of mature stands were the highest,which were 1.53g/kg,45.21g/kg and 154.38mg/kg respectively,16.39%,41.27%and 16.95%higher than those of the young stands without tending thinning.(7)The comprehensive score of soil nutrients of Chinese fir plantation in the sample plots with tending thinning was significantly higher than that in the sample plots without tending thinning.With the increase of the age of Chinese fir plantation,the comprehensive score of soil nutrients of Chinese fir plantation decreased first and then increased.Among them,the comprehensive score of soil nutrients of young stands was the highest,which was 0.8788,followed by that of mature stands,which was 0.6574,and that of middle-aged stands was the lowest,which was 0.3922.The comprehensive scores were sequenced as:young stands>mature stands>middle-aged stands.In the sample plots without thinning,the comprehensive score of soil nutrients of young stands was the highest,which was-0.5189,followed by that of mature stands,which was-0.5475,and that of middle forest was the lowest,which was-0.6179.(8)The typical correlation analysis of growth characteristics and soil nutrients of Chinese fir plantation with tending thinning showed that the correlation between total nitrogen,total phosphorus as well as available potassium and DBH,biomass as well as volume was significant.(9)In view of the cluster analysis and comprehensive evaluation analysis,46 monitoring standard plots can be divided into four categories:Category ? has the comprehensive evaluation value of soil nutrients of 0.7314-0.782,the average thinning intensity of 27.10%,the stands distributed in young,middle and mature ages and tending thinning time concentrated in 2011;Category ? has the comprehensive evaluation value of soil nutrients of 0.5516?0.6751,the average thinning intensity of 23.40%,the stands distributed in the young,middle and mature ages,and the tending thinning time distributed in 2011,2010 and 2009;Category ? has the comprehensive evaluation value of soil nutrients of 0.4192-0.5117,the average thinning intensity of 10.32%,stands mainly distributed in middle and mature ages,and the tending thinning time distributed in 2011,2010 and 2009;Category ? has he comprehensive evaluation value of soil nutrients of 0.2698-0.4115,no tending thinning,stands mainly distributed in middle and mature ages,and the tending thinning time distributed in 2011,2010 and 2009.(10)Through t-distribution inspection,the seven curve equations i.e.cubic,quadratic,composite,growth,index,logistic and linearity have all reached the extremely significant level(p<0.001).In particular,under the cubic function,the fitting longitude of the comprehensive score of soil nutrients of Chinese fir plantation with thinning intensity was the best,the correlation coefficient R2 was 0.660,y=1.472x-1.724x2-2.041x3+ 0.415,which could be used to estimate the change of soil nutrient comprehensive score with tending thinning intensity of Chinese fir plantation. |
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