神农架地区河岸带中领春木种群数量特征与空间分布格局

QUANTITATIVE CHARACTERISTICS AND SPATIAL DISTRIBUTION PATTERNS OF EUPTELEA PLEIOSPERMUM POPULATIONS IN RIPARIAN ZONES OF THE SHENNONGJIA AREA,CENTRAL CHINA

东亚特有珍稀濒危植物领春木(Euptelea pleiospermum)在神农架地区集中分布于河岸带中。为初步探讨领春木在河岸带集中分布的成因和维持机制,在神农架地区4条河流——沿渡河、香溪河、南河和堵河的河岸带,共设置了30个样方(20m×30m),从种群的大小级结构、静态生命表、存活曲线、空间分布格局及其动态5个方面分析了神农架地区河岸带中领春木种群的数量特征与空间分布格局。结果表明:1)幼龄期个体缺乏,中龄期个体相对丰富,老龄期个体数量稀少。纺锤型的大小级结构表明种群属于衰退型,但是以萌蘖为主要更新方式使其种群在较长一段时间内得以维持;2)现存的Ⅰ、Ⅱ级个体数少,导致静态生命表中Ⅰ、Ⅱ级个体死亡率出现负值,自疏现象造成第Ⅳ级个体出现死亡率高峰,由于接近实际寿命,在第Ⅶ级死亡率达到最高;3)虽然其幼苗存活率较低,但由于其幼树的存活率较高,其存活曲线接近DeeveyⅠ型,表明该地区河岸带的环境条件较适宜领春木种群的生长;4)空间分布格局总体为聚集分布,这与大多数珍稀植物种群一致。人为干扰和自然环境影响其分布格局,使种群由聚集分布向随机分布发展。因此使领春木种群在河岸带中沿海拔呈现"一带多岛"现象;5)从幼龄期到中龄期再到老龄期,不同发育阶段的领春木种群的分布格局由聚集分布逐渐变为随机分布。但由于分布格局受种群本身生物学特性、自然环境因素(如坡向和海拔)和人为干扰的影响,领春木在不同河岸带中的分布格局有所差异。

Aims Euptelea pleiospermum, an endangered tree species confined to East Asia, grows mainly in the riparian zones of the Yandu, Xiangxi, Nan and Du rivers in the Shennongjia area. We studied the quantitative characteristics, spatial distribution patterns and dynamics of E. pleiospermum populations. Our objectives were to explore the cause and mechanism that confmes the species to riparian zones and to provide a theoretical basis for conservation. Methods We placed 30 quadrats （20 m × 30 m） in the riparian zones of the four rivers. We recorded the diameter at breast height （DBH） and height （H） of each tree and divided them into seven size classes： Ⅰ, H〈 0.33 m; Ⅱ, H≥0.33 m and DBH〈 2.5 cm; Ⅲ, 2.5 cm≤DBH〈 7.5 cm, etc. Using the sides of the quadrat, we recorded the coordinates （x, y） of every E. pleiospermum individual. To analyze spatial distribution pattern dynamics, we divided trees into three stages： young （ Ⅰ and Ⅱ ）; middle-aged （Ⅲ and Ⅳ）; and old trees （Ⅴ-Ⅶ）. Important findings The spindle-shaped size class structure suggests that the populations of E. pleiospermum are declining, but E. pleiospermum can maintain its populations over long periods by sprouting. The mortality of size classesⅠ and Ⅱ is negative, indicating a shortage of size class Ⅰ and Ⅱ individuals. The two peaks of mortality at size classes Ⅳand Ⅶare caused by self-thinning and approaching the species＇ longevity, respectively. The survivorship curves of E. pleiospermum populations generally match Deevey Type Ⅰ, indicating that the habitat of the riparian zone is suitable for E. pleiospermum. The spatial distribution pattern tends to be clumped, but changes from clumped to random as a result of human disturbance and influence of the natural environment and gradually changes from clumped to random with growth from young to middle-aged to old trees.