高寒丘陵区不同退耕年限人工林形质评价

基于时空互代法研究不同退耕年限对青海东部人工林形质的影响，为高寒丘陵区人工林经营及多功能利用提供理论依据。在青海东部西宁市大通县设置青杨、祁连圆柏、青海云杉和华北落叶松典型人工林试验样地，开展退耕年限10、20 a和30 a样地调查。以生长情况、侧枝情况和土壤养分情况作为退耕还林林木形质评价指标，运用层次分析法构建林木形质的评价体系，对4种人工林林木形质进行综合评价。干形情况对林木形质的影响最大，贡献率占0.603；生长情况对其影响次之，贡献率占0.337；侧枝情况对其影响较小，贡献率仅占0.060；16个评价指标在林木形质评价中的权重大小依次为健康情况(0.674 9)＞自然整枝能力(0.598 8)＞土壤有机质(0.578 7)＞通直度(0.526 5)＞分杈情况(0.348 0)＞土壤K(0.232 5)＞侧枝平均基径(0.202 7)＞胸径年均生长量(0.176 9)＞枝粗指数(0.150 6)＞土壤N(0.139 2)＞树高平均生长量(0.107 6)＞高径比(0.071 5)＞尖削度(0.054 0)＞土壤P(0.049 6)＞侧枝数(0.047 9)＞冠径比(0.040 7)；综合评价得分依次为青杨(81.67)>华北落叶松(80)>青海云杉(75)>祁连圆柏(60)。森林生态系统通过自我调节,其发育呈正向演替。高寒丘陵区人工林形质随退耕恢复年限增加呈先增加后减少趋势。前期造林(10 a)可迅速提高林地盖度；发育至20 a时，林地林木形质最优；退耕30 a，林下光照减少，下层出现竞争缺光,影响林地涵养水分功能发挥，影响林木形质。以层次分析法建立的林木形质评价体系可为高寒丘陵区人工林经营及多功能利用提供依据，为其他树种形质评价提供借鉴。

Shape and Quality Evaluation of Planted Forest with Different Years after Conversion in Alpine Hilly Area

Based on the method of time-space mutual generation,this paper studied the influences of conversion years of farmland to the forest on the shape and quality of the artificial forest in the east of Qinghai Province to provide theoretical basis for the management and multi-functional utilization of the forest in the alpine hilly area.Experimental plots of typical plantations of Populus cathayana,Sabina przewalskii,Picea crassifolia,Larix principis-rupprechtii,and with the stand ages of 10,20,and 30 years old were set up in Datong county and Xining city located in Eastern Qinghai Province.Sixteen indices from three aspects,i.e.,the growth,lateral branches and soil nutrients were selected for the evaluations of stand shape and quality.An evaluation system was established by using the analytic hierarchy process (AHP) to conduct comprehensive evaluations of the stands of the four tree species above mentioned.The results indicated that the shape of the tree trunk demonstrated the greatest influence on the stand shape and quality (with a contribution rate of 0.603),the growth condition was the second (0.337),and the influence of lateral branches was insignificant (0.060).The weights of 16 indices in the shape and quality evaluation were in the order of health condition (0.674 9)>natural pruning ability (0.598 8)>soil organic matter (0.578 7)>straightness (0.526 5)>branching condition (0.348 0)>soil potassium (0.232 5)>average basal diameter of lateral branches (0.202 7)>annual average growth of DBH (0.176 9)>index of branch diameter (0.150 6)>soil nitrogen (0.139 2)>average growth of tree height (0.107 6)>ratio of height to diameter (0.071 5)>taperness (0.054 0)>soil phosphorus (0.049 6)>number of lateral branch (0.047 9)>ratio of diameter to crown (0.040 7).The scores of the comprehensive evaluations of the four tree species were in the order of P.cathayana(81.67)>L.principis-rupprechtii(80)>P.crassifolia(75)>S.przewalskii(60).The forest ecosystem presented positive succession through self-regulation.The shape and quality of plantations in alpine hilly area increased first and then decreased with the increase of time.It was concluded that forestation in the early stage (10 years) could rapidly increase the coverage of forest land; when it developed to 20 years,the shape and quality of the plantations were the best; after 30 years,the light under the forest reduced,the lower layers of the plantations competed for light,which affected the function of water conservation and the shape and quality of plantations.The evaluation system of forest shape and quality established by AHP in this study could provide a basis for the management and multi-functional utilization of artificial forest in alpine hilly area,and provide a reference for the evaluation of shape and quality of other tree species.