In order to test whether density dependence influences community diversity, a combination of manipu-lative experimentation and plot surveys were done usingCryptocaryaconcinna, a dominant species in subtropical evergreen forest. Twelve pairs of 1 m2 seedling plots were built around 12 adults, and plots were treated monthly with either a fungicide or a control. The surviving proportion ofC.concinna seedlings at different stages was cal-culated, and an analysis was conducted on the impact of fungicide on seedling survival and species richness. Correlation between relative abundance and community evenness at different ages was analyzed using plot sur-veys. The results showed that fungicide treatment decreased species richness of the seedling community by pro-moting the recruitment of common species. Furthermore, census of a 25 m radius around adultC. concinna trees confirmed that the density of saplings increased with distance from adults. Relative abundance ofC. concinna de-creased with increasing age, and decreasingC. concinna dominance resulted in an increase in community even-ness. To avoid the appearance of a single optimum population, the dominance ofC. concinna decreased with age via density dependence, and subsequently improved community species diversity.%本研究以南亚热带优势树种黄果厚壳桂(Cryptocarya concinna)为研究对象，采用控制实验与样地调查相结合的方法，验证密度制约对群落物种多样性维持的影响。通过在黄果厚壳桂母树周围建立24个成对的1 m×1 m幼苗样方，定期进行幼苗群落调查并做土壤杀菌，分析杀菌处理对黄果厚壳桂幼苗存活率及其幼苗物种丰富度的影响。并通过样地调查进行不同龄级相对多度与群落均匀度的相关分析。结果表明，杀菌处理可显著降低幼苗群落物种丰富度。黄果厚壳桂幼树密度随着离母树距离的增加而增加，其种群占整个群落的相对多度随着树龄呈递减趋势，黄果厚壳桂种群优势地位的减少将直接导致群落均匀度的增加，从而避免单优种群的发生，促进多物种共存。。
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