乌拉山自然保护区白桦种群的年龄结构和点格局分析
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1.乌海市林业局;2.内蒙古自治区林业科学研究院,内蒙古自治区林业科学研究院,内蒙古自治区林业科学研究院,内蒙古自治区林业科学研究院,内蒙古自治区林业科学研究院,内蒙古巴彦淖尔市乌拉山林场,内蒙古大学生命科学学院

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内蒙古自然科学基金项目(2011MS0609);国家"十一五"科技支撑计划项目(2008BADB0B05)


Age structure and point pattern of Butula platyphylla in Wulashan Natural Reserve of Inner Mongolia
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Inner Mongolia Academy of Forestry Science,Inner Mongolia Academy of Forestry Science,Inner Mongolia Academy of Forestry Science,Inner Mongolia Academy of Forestry Science,Inner Mongolia Academy of Forestry Science,Wulashan Forestry Station,Inner Mongolia University

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    摘要:

    白桦群落是乌拉山森林植被的主要类型之一,在高海拔阴坡、半阴坡以纯林形式分布.根据乌拉山自然保护区白桦林不同林龄结构设置3个典型样地,采用种群径级结构代替年龄结构、点格局分析(Ripley's K-Function)方法探讨了乌拉山白桦种群年龄结构、空间分布规律和种群动态.结果表明:(1)乌拉山自然保护区白桦种群径级结构呈典型的"金字塔"型,种群自然更新良好,属增长型种群;(2)由于种内不同个体间为争夺空间和资源,种群在第Ⅲ、Ⅳ径级死亡率较高,自疏作用明显;(3)白桦种群的存活曲线接近于DeeveyⅠ型曲线;(4)在研究尺度内白桦种群以幼树、中龄树为主时呈聚集分布,而成龄树或老龄树占多数时呈随机分布,即随着种群年龄的增加,其分布格局逐渐由集群分布向随机分布转变.乌拉山白桦种群在小于1.5 m的尺度呈聚集分布,即具有2株以上个体"丛生"现象.在环境条件相似的情况下,白桦种群自身的生物、生态学特性是影响其分布格局的最主要因素.

    Abstract:

    Plant populations comprise individuals of the same plant species existing in a specific area and time. Population structure and spatial patterns are important topics studied by population ecologists. In particular, monitoring plant population structure can help us understand the processes within and between different populations and identify drivers that control plant population dynamics. Analysis of the spatial distributions of populations is important because spatial patterns can reveal many biological characteristics of populations, their intra- and interspecific relationships with co-existing populations, as well as indicate factors underlying environmental factors and related concerns. Thus, population structure and spatial patterns are important indicators of population processes.
    We studied Betula platyphylla populations which dominate a mountainous area of forest vegetation on Wula Mountain of Inner Mongolia. Pure stands of this tree species are found on shaded or semi-shaded slopes at altitudes above 1800m. We analyzed the demographic structure and spatial patterns of B. platyphylla stands in the Wulashan Nature Reserve by establishing three 30m×30m sample plots, and classified older plants into three age groups: middle age, near maturity, and mature plants. Spatial clustering and population dynamics were examined over a range of distances between trees while using tree diameter classes serving as a proxy of tree age, and point pattern analysis (Ripley's K-function). Point pattern analysis is widely used for the research of population spatial distribution pattern and inter-species relationships at different scales. In this paper Ripley's K-function method, which is a type of point pattern analysis, is also used in this analysis. To derive age classes based on diameter, we selected one representative tree in each plot, measured the diameter at breast height (DBH) and later classified the trees into three classes (9.4, 15.7, and 19.0 cm DBH), did trunk analysis, measured their ages and grouped them into tree ages classes of 30, 54, and 90 years, respectively, and used these data for the basis of dividing the trees into diameter and age classes. Based on our analyses and other existing reports, we can classify the B. platyphylla population on Wula Mountain to eight diameter classes: seedling (class I), young trees (class II), middle aged-trees (classes III-IV), and mature trees (classes V-VIII).
    Our results suggest: (1) the demographic structure of the B. platyphylla population on the Wulashan Nature Reserve follows a typical "pyramid" shape suggesting a high regeneration rate and growth of many young plants in this population; (2) self-thinning is common in this population, which is explained by high intraspecific competition for space and resources and a higher death rate in age classes III and IV; (3) the survivorship curve of the B. platyphylla population is close to a Deevey I curve; (4) the B. platyphylla population exhibits an aggregated distribution when it is dominated by young and middle aged plants. Distributions are random when it is dominated by mature and old trees. Therefore, we predict that as the population matures, its spatial distribution will change from aggregated to random. We found spatial clustering occurs most strongly at distances of less than 1.5 m. This means two or more individual plants can form a cluster. Based on our findings we conclude the spatial patterns of the B. platyphylla population in this area of uniform environment conditions are controlled by biotic interactions and local ecological characteristics.
    In summary, we conducted a detailed analysis of the population age structure and spatial patterns of a B. platyphylla population in Wulashan Nature Reserve to elucidate peculiarities of population processes and their drivers. This paper attempts to provide a theoretical basis and help develop strategies for balanced natural resource protection in and around the Wula Mountain area. Our data can also serve as a starting point for more in-depth research.

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胡尔查,王晓江,张文军,海龙,张雷,张胜利,徐鹏雁.乌拉山自然保护区白桦种群的年龄结构和点格局分析.生态学报,2013,33(9):2867~2876

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