甘肃文县珙桐群落的区系组成结构特征

甘肃文县让水河流域的珙桐群落，是目前该种群自然分布的最北残遗。通过群落学特征分析研究表明：①该区域珙桐群落的植物约有种子植物１６９种，分属于６６科，１２３属；②地理成分复杂多样，温带分布型属约占７０．７％，并在群落各层的区系组成中均占居优势；③在群落中起重要作用的植物富有单型属和少型属，并多为白垩纪及第３纪植物区系的后裔或残遗；④该群落以单叶、中型叶及高位芽植物为基本外貌特征，隶属于北亚热带常绿、落叶阔叶混交林；⑤群落的成层现象明显，以乔木层和草木层较为发达，一般可分为２～３个亚层；⑥由于本区环境因子对该种群生态适应的临界性及自身繁殖和基因交流的障碍机制，珙桐后备种群缺乏，天然更新能力较差，群落的稳定性十分脆弱。

The Initial Study on Davidia Involucrata Community

Wen County in Gansu province is the northern distribution edge area of Davidia involucrata. By studying D. Involucrata phytocoenolgical characteristics, this paper proved that, D. Involucrata community′s species constitution is plentiful. There are about 169 seed plants belong to 66 families, 123 genera. The geographical compositions are complex. There are 13 kinds of genus distribution types. North subtropical distribution type is the main kind. The genera which have the most important effect in community are more the descendants and remains of the Cretaceous Period and Tertiary period floristic compositions. Single type and few type genera are comparatively more. The community is northern subtropical evergreen and deciduous broad leaved forest which mainly composed of single leaf, mesophyll and phanerophytes. Stratification of the community is clear. The arbor layer and field layer are developed, the can be divided into two or three sublayers. Because of the confine of environmental and ownself factors, D. involucrata′s natural regeneration activity is worse. The community steadily is weak.