| Reconstruction of low-efficiency forests through reasonable management measures can adjust their stand structure,improve the forest growth environment,increase forest land productivity,and promote the development of low-efficiency forests in a healthy direction.The thesis takes Suichuan County and Ningdu County of Jiangxi Province as the research area,and the low-efficiency Pinus massoniana plantations as the research object.Based on the analysis of the status quo of the low-efficiency plantations by consulting literature data,sample site investigation and sample determination.To clarify the reasons for the formation of low-efficiency Pinus massoniana plantations,and take replanting and thinning as examples,the improvement effect was analyzed through the changes in tree growth and soil physical and chemical properties after 7 years of replanting and 3 years of thinning.The research results can provide a reference for the quality improvement of low-efficiency Pinus massoniana plantations.The main research results and conclusions are as follows:(1)Based on the results of the second-category forest resource investigation and combined with field surveys,inefficient forest will be divided into low-density forest inefficient,high-density forest inefficient,ineffective forest soil poor and disaster-inefficient forest four types,which is mainly due to the"plucking and cutting",excessive logging,tending not timely thinning and other human factors,and the reasons for poor site conditions and natural disasters caused.The area of low-efficiency Pinus massoniana plantations in Suichuan County and Ningdu County in 2019 were 788.2 hm2and 4228.4 hm2,respectively,which were 417.2 hm2 and 3203.7 hm2 less than in 2009,and the quality of low-efficiency forests has improved compared to 2009.(2)After 7 years of replanting Schima superba,the average diameter at breast height(DBH),average tree height,and average volume of individual tree of the low-efficiency Pinus massoniana plantations increased by 0.8 cm,0.5 m,and 0.0018 m~3,respectively by47.06%,21.74%,and 45.00%compared with the control,and there were significant differences(P<0.05);After the low-efficiency Pinus massoniana plantations adopts thinning measures,the average DBH,average tree height,and average volume of individual tree in 3 years period increased by 0.5 cm,0.1 m,and 0.0041 m~3,respectively by 71.43%,6.67%,and 91.11%compared with the control.Among them,the average DBH and volume growth was significantly improved(P<0.05),but the average tree height was not significant(P>0.05).(3)After 7 years of replanting measures,the soil bulk density of each soil layer of the low-efficiency Pinus massoniana plantations decreased,but only the surface layer 0-10 cm significant difference(P<0.05).The increase in p H,organic matter,total nitrogen,total phosphorus,total potassium,available nitrogen,available phosphorus,and available potassium in the 0-10,10-20,and 20-30 cm soil layers are all greater than the contrast plot,with the exception of organic matter,total nitrogen,total phosphorus and available nitrogen content increased significantly in 0-10 cm soil layer(P<0.05),there was no significant difference(P>0.05).(4)Thinning reduced soil bulk density,increased soil porosity and soil water holding capacity,and both have significant effects in the 0-10 cm soil layer(P<0.05).After thinning,the p H,organic matter,total nitrogen,total phosphorus,total potassium,available nitrogen,available phosphorus,and available potassium content of the 0-10 and 10-20 cm soil layer increased more than the control in 3 years.Among them,only organic matter,total nitrogen,and available nitrogen content increased significantly in the 0-10 cm soil layer(P<0.05). |
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