广西北仑河口红树植物种群结构与动态特征

摘要

Population is not only the fundamental unit of a species for existence,adaptation,and evolution,but is also the link among individuals,communities,and ecosystems.Analysis of plant population structures can reflect the current state of populations,and help to reveal future population dynamics.In this paper,the population structure and dynamics of four mangrove species (Kandelia obovata,Aegiceras corniculatum,Avicennia marina,and Bruguiera gymnorrhiza) in the Beilun Estuary National Natural Reserve,Guangxi,were analyzed.This study illuminates the structural characteristics of populations and communities,as well as potential mechanisms driving the population dynamics of mangrove species,and provides a fundamental understanding and scientific basis for the protection and restoration of mangrove ecosystems in Guangxi,southern China.Using survey data from 12 permanent plots (each 20 m × 20 m),in this study we analyzed the height class,size class,static life tables,survival curves,and time sequences to describe and predict the population structure and dynamics of four mangrove species.Seven aggregation intensity indexes,including mean crowding index,clumping index,patchiness index,etc.,were applied to analyze the spatial distribution pattern of mangrove plants with different size classes.The height structure and size structure analyses indicated that seedlings and saplings of B.gymnorrhiza and K.obovata were relatively abundant,and also that their populations showed robust regeneration.The regeneration of A.corniculatum was hindered to some extent,and there were fewer adult plants,although the quantity of seedlings and the overall population were relatively stable.There were fewer individuals and no seedlings in the A.marina population,which showed poor regeneration and an obvious decline.The static life table analysis showed that the survival of different age classes of the four mangrove plant species differed greatly,and that the survival and life expectancy gradually decreased with increasing age.The survival curve analysis suggested that A.marina showed a Deevey type Ⅰ curve,and all individuals reached the average physiological life expectancy.B.gymnorrhiza and K.obovata showed Deevey type Ⅱ curves,and individuals of different age classes had relatively consistent death rates.The survival curve of A.corniculatum fell between the Deevey type Ⅰ and the Deevey type Ⅱ curves,and while the death rates of young age classes were relatively high,they gradually stabilized after reaching middle age.Through time sequence analysis,it was predicted that the population of A.marina would decrease;the number of young individuals of A.corniculatum would decrease and that of adult individuals would increase,and the population size in the future would display a stable trend with a slight decline;and the number of young individuals of B.gymnorrhiza and K.obovata would increase,and the population size within different age classes would regenerate well;hence,their future population sizes are predicted to increase.The calculations of seven aggregation intensity indexes demonstrated that populations of different age classes of the four mangrove plant species mainly exhibited clumped distributions,and the aggregation intensity always tended to decrease with increasing age.The population dynamics of the four mangrove species and succession stages of the mangrove communities were closely related.The population of the pioneer plant,A.marina,was in a stage of relatively rapid depression,and the population of A.corniculatum,typical of early and middle succession stages,was stable with a slight decline.The populations of B.gymnorrhiza and K.obovata,typical of middle and late succession stages,displayed growth of various degrees.These results suggested that the mangrove communities investigated in this study were in the middle stage of succession,and that A.marina and the association of A.marina and A.corniculatum will gradually give way to an association dominated by B.gymnorrhiza.The population dynamics of mangrove plants were regulated by multiple factors such as habitat condition,intra-and inter-species competition,and insect pests.The clumped distribution of the four mangrove plants at different age classes was closely related to their reproduction modes and habitat conditions.The gradual decrease of aggregation intensity with increasing age might be caused by self-thinning,or thinning effects as a result of intensified intra-or inter-species interactions.%以广西北仑河口国家级自然保护区4种红树植物秋茄(Kandelia obovata)、桐花树(Aegiceras corniculatum)、白骨壤(Avicennia marina)和木榄(Bruguiera gymnorrhiza)为研究对象,在野外样地调查的基础上,采用高度级和大小级结构、静态生命表、存活曲线、时间序列分析和7种聚集强度指数等方法对4种红树植物的种群结构和动态进行了分析和预测,旨在阐明红树植物种群与群落的结构特征和动态变化规律以及潜在的驱动机制,为广西红树林生态系统的保护与恢复提供基础资料和科学依据.研究结果表明:木榄和秋茄种群更新良好,桐花树更新受到一定阻力,种群相对稳定,白骨壤种群更新不良,呈现明显的衰退趋势;4种红树植物种群不同龄级的存活量差别较大,存活量和生命期望一般随龄级的增加逐渐减少;白骨壤种群的存活曲线属于Deevey Ⅰ型,其种群个体均能达到其平均生理寿命,木榄和秋茄种群属DeeveyⅡ型,各龄级个体具有相对一致的死亡率,而桐花树种群介于Deevey Ⅰ型和DeeveyⅡ型之间,其幼龄期死亡率偏高,中龄期后死亡率逐渐接近;时间序列分析同样表明,白骨壤未来种群数量将明显降低,种群逐步衰退,桐花树未来种群数量将表现为稳中有降,而木榄和秋茄未来种群数量将趋于增加.4种红树植物不同龄级种群多呈现聚集分布,聚集强度往往随种群龄级的增加而趋于降低.上述结果表明,北仑河口4种红树植物的种群动态与群落所处演替阶段息息相关,先锋植物白骨壤种群处于较快衰退阶段,演替前中期的桐花树种群稳中有降,而演替中后期的秋茄和木榄种群出现不同程度的增长,反映出本次调查的红树林群落正处于演替的中期阶段,白骨壤和白骨壤+桐花树群丛将逐步演替为以木榄为优势种的群丛.此外,红树植物的种群动态受到自身繁殖特性、生境条件、种内和种间竞争、虫害等多种因素的调控.