贵州雷公山秃杉种群生活史特征与空间分布格局

秃杉是一种珍稀濒危植物,以斑块状分布于雷公山东南面斜坡海拔800-1300 m之间的沟谷两侧。从年龄结构、生命表特征、存活曲线以及种群不同龄级个体空间分布格局等方面研究了雷公山秃杉种群生活史特征与空间分布格局。研究结果表明:秃杉的种群结构存在波动性,成年阶段个体较丰富,幼苗与老龄数目相对较少,秃杉自身的生物学特性及环境因素是形成这种现象的主要原因;秃杉种群存活曲线趋于DeeveyⅡ型,出现2个死亡率高峰,一个出现在第6龄级阶段,另一个出现在第12龄级阶段,期望寿命单调下降;秃杉种群空间分布格局总体上为聚集分布,处于不同发育阶段的秃杉种群,其分布格局随时间而发生变化,从幼龄期到中龄期再到老龄期,种群分布格局由聚集分布逐渐变为随机分布,秃杉种群在不同发育阶段的空间分布格局差异与其生物学和生态学特性密切相关,同时受群落小环境的影响。

Life history and spatial distribution of a Taiwania flousiana population in Leigong Mountain, Guizhou Province, China

Aims: We studied the life history and distribution of a Taiwania flousiana Gaussen population in Leigong Mountain,Guizhou Province,China,to explain population growth characteristics,and how biological and environmental factors affect population distribution and dynamics.Methods: T.flousiana,a rare and endangered plant,is distributed in patches on southeastern facing slopes at altitudes of 800—1300m on Leigong Mountain.We sampled trees in 30 plots(30m × 30m),and in each plot,we established 9 subplots(10m × 10m) to measure the shrubs,grasses and regeneration of this species.We recorded the diameter at breast height(DBH) of each tree,and then divided them into 13 size classes: S1,H ≤ 2.5m(DBH < 5.0cm);S2,H > 2.5m(DBH < 5.0cm);S3,5.0cm ≤ DBH < 10.0cm;S4,10.0cm ≤ DBH < 15.0cm;S5,15.0cm ≤ DBH < 20.0cm,and so on.We recorded the location of every T.flousiana individual using coordinates(x,y) within each subplot.We determined the population size and structure,life expectancy and survivorship curve of T.flousiana to analyze population structure and dynamics. Important findings: Because T.flousiana seedlings and big trees were rare,the structure and size classes of the population indicate the T.flousiana population is in decline.This appears to be caused by the species biological characteristics and environmental factors.The survivorship curve of this T.flousiana population generally matches the Deevey II type.There are 2 peaks of mortality in the 6th and 12th size classes caused by intraspecific competition for resources and physiological aging,respectively.The life expectancy of this species decreased monotonically during its life span,although T.flousiana seedlings and big trees were rare and had low survival rates.The species generally has a clumped distribution pattern,but this gradually changes over time from a clumped to a random pattern as trees matures from young to middle-aged to old trees.Populations tend to be clumped in the first five size classes,and are distributed-randomly from the 7th size class to the 13th size class.These different developmental stages were related to the biological and ecological characteristics of the species and to microenvironmental conditions.Meanings: We conclude T.flousiana conservation strategies should focus on seedling establishment and conservation,reducing human disturbance and enhancing genetic diversity between populations.