重庆喀斯特生境中桢楠种群结构与动态特征

Population structure and dynamic characteristics of Phoebe zhennan S.Lee in karst areas of Chongqing

桢楠是我国珍稀渐危树种,国家二级保护植物,野生多散生于海拔1500 m以下的亚热带常绿阔叶林中。而喀斯特生境岩石裸露、土壤浅薄贫瘠、岩溶干旱频发,理论上并不适合喜湿耐荫且喜酸性土壤的桢楠生长及幼苗更新。因此重庆市大足区和永川区喀斯特生境中的天然桢楠种群可能存在一定的更新困难。为明确这两个桢楠种群的生存现状及动态特征,采用野外调查法,从径级结构、静态生命表、存活曲线、结构动态及分布格局等方面分析桢楠种群结构及其数量动态规律,以期预测种群未来发展趋势,为喀斯特地区桢楠种群的保护、群落更新及植被恢复提供理论基础。结果表明:(1)大足区桢楠种群的年龄结构趋于稳定型,而永川区桢楠种群的年龄结构为增长型。两地区幼苗充足但死亡率高。(2)静态生命表及相关曲线分析显示,两个桢楠种群存活数量总体上随径级增大而减少;两个桢楠种群的生存期望值在不同径级间存在波动,大足区桢楠种群在第Ⅱ径级而永川区则是第Ⅳ径级期望值最高。(3)两个种群的存活曲线均为Deevey-Ⅲ型,即幼树死亡率较高,并且种群的增长速度较为缓慢。(4)大足区种群为随机分布,永川区种群为集群分布;种群各生长发育阶段均为集群分布,但聚集强度随着龄级的增加而减弱。桢楠种群在喀斯特地区生长周期长,天然更新能力较强但对外部干扰敏感。建议加强对幼苗的抚育工作,提高幼苗存活率,促进桢楠种群的自然更新和恢复。

Phoebe zhennan S.Lee is a rare and endangered tree species in China,a nationally protected secondary plant.It is mostly scattered in the wild in subtropical evergreen broad-leaved forests below 1500 m above sea level.As the primary populations are almost destroyed,the existing resources are limited and scattered.Karst habitat has exposed rocks,shallow and barren soil and frequent drought.In theory,it is not suitable for the growth and seedling regeneration of P.zhennan,which likes humidity,shade and acid soil.Therefore,it may be difficult to renew the natural P.zhennan population in karst habitats in Dazu District and Yongchuan District of Chongqing.To explore the survival status and distribution model of the two P.zhennan populations,the field survey method is used to analyze the structure and the dynamic law of the populations and their quantity,by assessing the diameter structure,static life table,survival curve,structural dynamics and distribution pattern.It is hoped that the future development trend of the population can be predicted,and the theoretical basis for the protection,community renewal and vegetation restoration of the karst area will be provided.The results showed that:(1)the age structure of P.zhennan population in Dazu District tended to be a stable type,while it was an increase type in Yongchuan District.Both areas had abundant seedlings but with high mortality rates.(2)The individual numbers of both populations of P.zhennan generally decreased with the diameter class increased.The life expectation of the two P.zhennan populations fluctuated between different diameter classes.It was the highest in the diameter classⅡin the population of P.zhennan in Dazu District,while it highest in the diameter classⅣin Yongchuan District.(3)Both populations had Deevey-Ⅲtype survival curves,that was,the mortality of young trees was relatively high,and a relatively low population growth rate.(4)The population in Dazu District was randomly distributed,while that of the Yongchuan District was consolidated.P.zhennan were clustered populations at the growth and development stage,but their strength weakened with the growth of the age group.The population of P.zhennan in the karst region had a long growing time,a strong capacity for natural regeneration but sensitive to external disturbances.It is suggested to enhance seedling selection and improve seedling survival to promote natural renewal and restoration of P.zhennan population.