残存银杏群落的结构及种群更新特征

银杏是现存裸子植物中最古老的孑遗植物,也是银杏纲植物现存的唯一种,但其自然群落和种群生态学特征至今尚未明晰。对分布于贵州省和重庆市交界的大娄山区7个地点的残存银杏群落的物种组成、垂直结构、主要组成种的种群大小级结构等群落结构特征以及银杏种群更新特征进行了研究。林木层共记录到82个种,其中常绿针叶树3种,常绿阔叶树和落叶阔叶树分别为37种和42种;各群落中相对优势度均以落叶阔叶树为高,银杏在7个样方中为顶极优势种,其中在6个样方中为单优势种。银杏群落林木层在垂直结构上一般可分为3层,银杏为乔木层的主要成分。各个群落中银杏种群的大小级结构均为逆-J型或多峰型,更新连续,而其余种类多为单峰型。不同微地形单元上银杏具有不同的萌枝特性,沟谷生境中银杏的萌枝率显著高于下部边坡和崖锥,有萌个体率的差异是主要的贡献因子,而银杏的萌枝能力与主干的胸径无显著关联。残存银杏群落为典型的发育在不稳定立地上的落叶阔叶林地形顶级群落,银杏通过萌枝维系种群的长期存留和群落的相对稳定。群落中银杏、红豆杉(Taxus chinensis)、红椿(Toona ciliata)和川黄檗(Phellodendron chinense)等多种珍稀濒危植物共存,有必要从群落层次上加强对残存银杏群落的保护。

Community structure and population regeneration in remnant Ginkgo biloba stands

The living fossil species Ginkgo biloba is the sole survivor of the once moderately diverse Gingoalean clade. The natural ecology traits of this species at population and community level are still largely unknown. Seven remnant stands of G. biloba on Mt. Daloushan located on the boundary of Guizhou Province and Chongqing Municipality were investigated and it's community structure characteristics including floristic composition, stratification structure, size structure of main species were analyzed, as were the regeneration characteristics of G. biloba. Eighty two vascular species were recorded in the woody layer; the number of conifers, evergreen broad-leaved trees and deciduous broad-leaved trees were 3, 37 and 42, respectively. Deciduous trees accounted for the vast majority of the relative dominance, and G. biloba was the top dominant species at all stands. The stratification structure of the woody layer at the stands could be distinguished into three layers with G. biloba as the main component of the canopy layer. The size frequency distribution of G. biloba was of the inverse-J type or sporadic type suggesting the possibility of good regeneration, while most of the other main species showed a unimodal pattern indicating weak regeneration. Sprouting traits varied among the G. biloba populations in differing micro-landforms. The ratio of the number of all sprouts to that of main stems was significantly higher in the valley habitat than in the other two areas, the lower side slope and the talus, the proportion of sprouting individuals being the main determination factor. The diameter of the main stem of each individual clone was independent of the total number of stems in that clone. The remnant G. biloba community is seen to be a specifically topographic climax community type developing on unstable micro-landforms which are well watered and well drained. Vegetative reproduction by means of sprouts may have contributed to the extraordinary persistence of G. biloba and the relative stability of the community. Community-level protective measures should be considered, for there are several other endangered species, such as Taxus chinensis, Toona ciliate and Phellodendron chinense living together with G. biloba.