Abstract:

AimsEuptelea 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 confines 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 andDBH < 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 (Ⅰand 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. pleiospermumcan maintain its populations over long periods by sprouting. The mortality of size classes Ⅰ and Ⅱ is negative, indicating a shortage of size class Ⅰ and Ⅱ individuals. The two peaks of mortality at size classes Ⅳ and Ⅶ are 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.

Key words: Euptelea pleiospermum, riparian zone, quantitative characteristic, spatial distribution pattern, Shennongjia