[Objective] A new storey identification method--Maximum Light Receiving Plane (MLRP) method was developed to identify forest story of typical natural broad-leaved forests in mid-subtropical zone in accordance with whether the tree crowns could receive sunlight directly and the extent of direct sunlight the crowns received,which provide a new way in revealing the patterns of vertical structure of the natural broad-leaved forests in mid-subtropical zone.[Method] The typical natural broad-leaved forests in mid-subtropical zone could be identified as Light Receiving Storey (LRS) and NonLight Receiving Storey (NLRS) by the MLRP method.The LRS could be separated further by ward method of cluster analysis according to tree height.[Result] The five sample plots of typical natural broad-leaved forests in mid-subtropical zone were divided into LRS (Ⅰ) and NLRS (Ⅱ) by the MLRP method,LRS comprised substorey Ⅰ1 and Ⅰ 2.The results of MLRP method of the five sample plots indicated that the height of interface between LRS and NLRS (i.e.the height of the interface between storey Ⅰ and Ⅱ) were 17.0,16.5,17.0,17.0,and 16.0 m,and the height of interface between substorey Ⅰ 1 and Ⅰ 2 were 25.0,27.0,25.0,22.9,and 25.0 m,respectively.The volume of per hectare of various substoreys,height difference between adjacent storeys and the mean diameter at breast height of various substoreys all conformed to National Standards (GBT 26424-2010) when the storeys were identified by the MLRP method.[Conclusion]The MLRP was proven by CVPA-H curves,it is a simple and practicable field operation without measuring heights of all trees but just by judging whether the tree crowns received direct sunlight and whether the tree crowns were evidently outstanding in the stand (i.e.the extent of direct sunlight received).Comparisons of the storey identification by MLRP method with profile diagram,the changes of variation coefficients of height of different storey identified,and whether the calculations of stand description factors at substoreys conforming to storey identification of the National Standards (GBT 26424-2010) further proved that the MLRP method was scientifically sound.The MLRP method could better reflect the patterns of natural differentiation of vertical structure of the natural broad-leaved forests in mid-subtropical zone.It also reflected the consequence of competition among trees for light and spatial resource,implying a biological significance.%[目的]依据林木树冠是否接受到垂直光照和林木树冠接受到垂直光照的程度提出林层划分新方法——最大受光面法,为揭示中亚热带天然阔叶林垂直结构的自然分异规律提供新方法.[方法]在典型中亚热带天然阔叶林中,采用最大受光面法将林分划分为受光层和非受光层;在受光层中,以林木树高为聚类因子采用离差平方和法(ward法)对受光层进一步分层.[结果]通过最大受光面法将5块典型中亚热带天然阔叶林标准地划分为受光层Ⅰ和非受光层Ⅱ,其中受光层包括Ⅰ1和Ⅰ2亚层;最大受光面法林层划分结果显示,5块标准地的受光层和非受光层的分界面高度(即第Ⅰ,Ⅱ层分界面高度)分别为17.0,16.5,17.0,17.0和16.0 m;Ⅰ1和Ⅰ2亚层的分界面高度分别为25.0,27.0,25.0,22.9和25.0 m;划分林层后,Ⅰ1,Ⅰ2和Ⅱ层的每公顷蓄积量,相邻的Ⅰ1,Ⅰ2和Ⅱ层间的高差和Ⅰ1,Ⅰ2,Ⅱ层平均胸径均符足林层划分国家标准(GBT 26424-2010).[结论]CVPA-H曲线的变化规律证实了最大受光面的存在,在野外只需判断林木树冠是否接受到垂直光照和林木树冠是否明显突出(即接受到垂直光照的程度)即可实现林层划分,无需测量每株林木树高,野外操作简单易行;林层划分结果与剖面图判断结果的对比和各层测树因子都符合林层划分国家标准(GBT 26424-2010)等,验证了最大受光面法划分林层的科学性;最大受光面法能较好地反映中亚热带天然阔叶林垂直结构的自然分异规律,该方法依据林木树冠是否能接受到垂直光照和接受到垂直光照的程度进行林层划分,体现了林木对垂直光照和空间资源竞争的结果,具有一定的生物学意义.
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