海南苏铁种群结构与森林群落郁闭度的关系

Population structure of Cycas hainanensis and its relationship with forest canopy density

海南苏铁(Cycas hainanensis)是古老的苏铁属植物,为国家Ⅰ级重点保护植物,也是IUCN红色名录的濒危物种。为研究海南苏铁在海南昌江保梅岭省级自然保护区的种群结构与森林郁闭度的关系,本文通过样方法对海南苏铁种群及其所在群落进行调查,分析了其群落结构和物种多样性,以及其种群密度、年龄结构、存活曲线、空间分布格局与森林郁闭度的关系。结果表明:海南苏铁所在群落垂直结构分为乔木上下2层、灌木层和草本层。海南苏铁所在群落物种多样性指数偏高,群落内物种组成丰富;各样方内海南苏铁数量分布不均,经常群生于海拔500m左右的林下、林缘间。海南苏铁种群结构属于增长型,种群更新力强,种群存活曲线趋近于Deevey-II型,死亡率随着龄级增加而增加,说明海南苏铁种群处于相对稳定的状态,随着种群个体的生长发育,其生存力逐渐下降;海南苏铁种群空间分布格局呈聚集型,聚集程度指标随着林分郁闭度变大而增加。曲线估计结果显示,海南苏铁幼苗幼树在透光率36.11%–58.33%显著增加。综上所述,昌江保梅岭地区的海南苏铁种群处于较为稳定的增长状态,喜生长于海拔500 m左右、郁闭度为35%–60%的森林环境中。

Aim: Cycas hainanensis, an ancient species of Cycas, is a top priority plant species in China and is also classified as endangered by the International Union for Conservation of Nature(IUCN) Red List. We aim to study the relationship between population structure and forest canopy density of C. hainanensis in the Baomeiling Provincial Nature Reserve of Changjiang County, Hainan Province.Methods: After an investigation of the C. hainanensis population and its community by utilizing the sample survey, we analyzed community characteristics including structure and species diversity, and population characteristics such as age structure, survival curve, spatial patterns, and population density. We also studied the relationship between C.Results: The vertical structure of the community of C. hainanensis was divided Sintcoi tewon tcreee layers, shrub layer and herb layer. The species diversity index of the community was high and the community species composition was rich.The distribution of C. hainanensis was uneven in all quadrats and formed clusters in the undergrowth as well as the ability is strong. The population survival curve of C. hainaBneinsois dteinvdeed rtos tihte yD eevey-II type. The population mortality increased with age, which indicated that the population of C. hainanensis was in a state of stable growth. Thepopulation viability decreased with the growth and development of individual specimens. The spatial distribution pattern of C. hainanensis population conformed to clumped distribution, and the degree of aggregation was positively correlated with an increase of forest canopy density. A curve estimation demonstrates that the density of C. hainanensis seedlings and saplings increased significantly in the study area where forest canopy density was 36.11%–58.33%. Conclusions: In conclusion, the C. hainanensis population in the Baomeiling Provincal Nature Preserve of Changjiang County is in a stable growth state and preferred to grow in a forest environment with an elevation of approximately 500 m and forest canopy density of 35%–60%.