甘肃文县珙桐群落优势种种群分布格局及动态变化趋势

甘肃文县珙桐群落优势种种群分布格局主要表现为随机分布，仅在与包果石栎、青冈组成的群落中其种群表现为集群分布。分析优势种个体百分率与胸径径级的关系表明：分布于碧峰沟上源和范坝竹园沟珙桐群落内的珙桐幼年个体百分率极低，随着时间的推移，将失去优势种地位，而以伴生种形式存在于其它增长型优势种群形成的常绿、落叶阔叶混交林中；分布于石磨河上源的珙桐群落，珙桐、千金榆为增长型种群，亮叶桦、白桦无幼年个体，为衰退种群，经过一定时期，二者将不再为优势种，逐渐从群落中消逝。

Population Patterns and Dynamics of Davidia involucrata Community's Dominant Species in Wen County of Gansu

In the Davidia involucrata community in Wen county of Gansu province, most of the dominant's population patterns show random dispersion, expect only that in the community composed of Lithocarpus cleistocarpus, Quercus glauca and D.involucrata, the population pattern D.involucrata's is aggregated dispersion. Analysing the relationship of dominant numbers percentage and stand class shows that, in the community distributed in Bifenggou upper reaches and Zhuyuangou, D.involucrata infancy numbers percentage is very low. As time pass it would lose the position of dominant, and become a associated species existing in the evergreen and deciduous broad-leaved forest formed by other growing populations. In the community distributed in Shimohe upper reaches, D.involucrata and Carpinus cordata are growing populations. Betula luminifera and Betula platyphylla haven't infancy numbers and both are decline populations. Through a definate period, they will not be dominants, and gradually disappear from the community.