Over the past decade,the Chinese Forest Biodiversity Monitoring Network established large stem-mapping plots located along a latitudinal gradient from temperate to subtropical and tropical forests.The forest dynamics plot is as an important platform to monitor forest biodiversity.This approach enables collection of detailed data to understand the changes in biological diversity,forest community structure,and underlying mechanisms of species coexistence.Communities in the ecological transition zone between adjacent climatic zones tend to possess the characteristics of the adjacent area and also show unique and high species richness.Thus,it is critical to thoroughly investigate the community characteristics in the transition zone.Vegetation is well-preserved in the deciduous broad-leaved forest of the Baiyunshan Nature Reserve.The vegetation in this area is influenced by the transition from a north subtropical zone to a warm temperate zone.The community structure is relatively complex,with abundant species diversity.In 2015,the technical specifications of Barro Colorado Island in Panama were used to establish a 5-ha forest dynamics plot in the Baiyunshan Nature Reserve of Henan Province,central China,and the first survey has now been completed.Woody plants with a diameter at breast height (DBH) ≥ 1 cm were tagged,measured,and identified to species.In the present study,the species composition,diameter class structure,importance value,community classification,and distribution pattern of the data from the first survey were analyzed to count and identify novel species.The following conclusions were reached based on the results of the survey.(1) The plot contained 17963 individual trees (DBH ≥ 1 cm) from 34 families,55 genera,and 93 species.(2) Quercus aliena var.acuteserrata,Pinus armandii,and Lindera obtusiloba occupied dominant positions in the community.Rare species accounted for 36.56％ of the total number of species,whereas the occasional species contributed 30.11％ to the total.(3) The distribution of all species based on the diameter class structure presented an inverted "J" type,implying abundant seedlings in the community indicating that community renewal is proceeding well.(4) Based on cross-validation of the multiple regression tree,the vegetation was divided into three classes according to the degrees of concavity and convexity,as well as the average altitude,Ⅰ,Quercus aliena var.acuteserrata-Pinus armandii-Lindera obtusiloba-Litsea tsinlingensis-Malus honanensis;Ⅱ:Quercus aliena var.acuteserrata-Pinus armandii-Toxicodendron vernicifluum-Forsythia suspensa;and Ⅲ:Quercus aliena var.acuteserrata-Betula platyphylla-Symplocos paniculata-Rhododendron micranthum.(5) Point-pattern analysis showed that the distribution pattern of the dominant species is mainly aggregated within the plot.These results improve the current understanding of this forest community in a temperate-subtropical transition zone.This study also provides basic data for use in the management and protection of the plant community in this forest.The complex distribution of plant communities and species coexistence require long-term continuous monitoring and exploration.Research on the Baiyunshan plot has only just begun,and much more work is required to determine the forest canopy structure,pedigree of plant functional traits,community structure,and mechanisms maintaining biological diversity,among others.The Baiyunshan plot will hopefully serve as a platform to understand the species coexistence of a forest community in an ecological transition zone.This work will provide technical support for the business,management,and biodiversity protection of the area.%白云山落叶阔叶林是暖温带-北亚热带生态过渡区保存较完好的植被,具有北亚热带向暖温带的过度性质,群落结构相对复杂,物种种类相对丰富.参照巴拿马巴洛科罗拉多岛(Barro Colorado Island,BCI)样地的技术规范,于2015年在白云山国家森林公园建立了一个5 hm2固定监测样地,调查并鉴定了样地内胸径≥1 cm的木本植物.基于首次调查数据从物种组成、径级结构、重要值、群落分类和分布格局等方面进行了分析,结果表明:(1)样地共有17963株个体,隶属于34科55属93种;(2)该群落以锐齿槲栎(Quercus aliena var.acuteserrata)、华山松(Pinus armandii)、三桠乌药(Lindera obtusiloba)、漆树(Toxicodendron vernicifluum)占优势,稀有种占总种数的36.56％,偶见种占总种数的30.11％;(3)所有物种的径级结构分布呈倒“J”型,表明群落内有充足的幼苗,群落更新状况良好;(4)多元回归树经过交叉验证,以凹凸度和平均海拔将样地植被划分为3类,Ⅰ:锐齿槲栎-华山松-三桠乌药-秦岭木姜子-河南海棠群落;Ⅱ:锐齿槲栎-华山松-漆树-连翘群落;Ⅲ:锐齿槲栎-白桦-白檀-照山白群落;(5)点格局分析表明样地内优势种主要表现为聚集分布格局.研究结果有助于增加人们对暖温带-北亚热带生态过度区内森林群落的认识,为此区域内植物群落的管理和保护积累基础资料.
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