Comparative study on population age structures betweenAdenophora lobophylla andA. potaninii

Abstract

Comparing with an affinity and widespread speciesAdenophora potaninii, the age structures of A.lobophylla population, an endangered plant species were studied. 29 sample plots were investigated in the centered distribution area, Jinchuan county from altitude 2 300 m to 3 400 m. The main factors which influence the population age structures of A.lobophylla were analyzed. The principal characteristics of A.lobophylla populations are that the number of seedling and the density of population are much less than these of A.potaninii population. Below altitude of 2 700 m, the age structures of most A.lobophylla populations show the declining status, only above altitude of 2 700 m they are stable, while age structures of all populations of A.potaninii populations at corresponding altitude perform stable and developing features. The age structure patterns, relations between age (x) and number of individual (y) of stable populations of A.lobophylla can be expressed by equation: y =e(^a-bx), and the longest life span is 25a. Whereas A.potaninii populations can be expressed by the equation: y =ax^-b, and the longest life span of individual is 21a. The external factors, which constrain the extension of A.lobophylla population, are extreme environmental conditions such as serious drought, external disturbance and low temperature.