极小种群梓叶槭种群结构及动态特征

【目的】分析中国特有濒危极小种群梓叶槭(Acer catalpifolium)的年龄结构和动态特征,揭示种群与环境之间的相互关系,预测种群发展动态,探索其濒危机制,提出野生梓叶槭种群的保护和恢复对策。【方法】通过对集中分布于四川峨眉山和都江堰的梓叶槭种群进行样地调查,采用样方调查法,将各样地划分为1～4个20 m×20 m的样方,再将每块样方划分为16个5 m×5 m的小样方; 对样方内的梓叶槭植株进行每木调查,调查内容包括个体数、树高、胸径等生长因子,同时记录各样地海拔、经纬度、坡向、坡度、林分郁闭度、植被群落以及土壤类型等生境因子; 以梓叶槭个体的胸径代替龄级来反映种群结构,将梓叶槭胸径大小划分为11个径级(Ⅰ-Ⅺ,设置DBH>50 cm为Ⅺ级,每级间隔5 cm),龄级与胸径大小级对应,绘制梓叶槭种群的径级结构图; 编制了种群的特定时间生命表,分析其存活曲线、死亡率曲线等重要参数; 运用时间序列预测模型分析种群数量动态和发展趋势。【结果】梓叶槭在峨眉山和都江堰地区的种群差异明显,峨眉山种群共有105株,都江堰种群共有81株,种群龄级结构完整,种群径级结构表现为中龄级所占比例较大、幼龄级和老龄级比例次之的纺锤形结构。梓叶槭种群年龄结构动态变化指数表明,两个地区受随机干扰时的种群年龄结构动态指数(V_pi')分别为0.011 6和0.004 2,均趋近于0,总体上表现出由稳定型向衰退型转化的衰退型结构; 生命表及相关曲线分析显示,梓叶槭早期个体死亡数较高,存活数随龄级的增加而减少,对环境的选择作用强; 存活曲线趋于Deevey-Ⅱ型,各龄级种群有相近死亡率; 生存函数分析表明,两个种群的生存率函数S(t)均随着龄级的增大呈单调下降的趋势,而累计死亡率F(t)则呈单调上升趋势,两个函数曲线变化呈现互补的现象; 时间序列预测分析表明,2、4、6、8龄级时间后梓叶槭老龄级个体逐渐增多,幼龄级个体则有所降低,种群稳定性降低,难以长期维持; 如果种群中幼苗难以补充,幼树不充足,再经过4个龄级后梓叶槭种群将成为衰退型种群。【结论】导致梓叶槭濒危的原因可能是梓叶槭的生物学特性和人为干扰; 应加强对梓叶槭种群及栖息地的保护,保护梓叶槭现有的成年个体,促进种子的萌发和幼苗的更新,防止栖息地及生态系统的破坏; 还要深入开展梓叶槭生物学及繁育特征研究,提高梓叶槭种子萌发率和成苗率,促进其种子向幼苗转化。另外,在天然林更新中,应采取人工抚育等措施来加强对中小径级梓叶槭个体及生境的保护,促进梓叶槭种群的自然更新和恢复。

The population structure,dynamics features and protection strategy of Acer catalpifolium extremely small population

【Objective】We analyze the age structure and dynamic characteristics of Acer catalpifolium, a unique endangered species in China, reveal the relationship between A. catalpifolium populations and their environment, predict the patterns of population dynamics, explore its endangered mechanism, and propose protection and restoration strategies for wild populations.【Method】A. catalpifolium trees in Emeishan and Dujiangyan, Sichuan Province were studied by field investigation, the method of sample square survey was adopted. The sample area were divided into 1 to 4 samples square of 20 m × 20 m, and then each sample square was divided into 16 small squares of 5 m × 5 m. The A. catalpifolium in the sample square were investigated per wood, investigation content includes some growth factors such as the number of individuals, height of tree, DBH(diameter at breast height), and some habitat factors were recorded such as altitude, latitude, longitude, slope direction, slope, forest canopy density, soil type and vegetation community, the DBH of A. catalpifolium was used to represent age class to reflect the population structure, the DBH size of A. catalpifolium was divided into 11 diameter classes(Ⅰ—Ⅺ; D_DBH>50 cm is grade Ⅺ, and the interval of each stage is 5cm), the age class corresponds to the DBH class. The diameter class structure chart was drawn, time-specific life table of the population and important parameters(survival curve and mortality curve)were built and analyzed, the population dynamics were predicted by time series model.【Result】The populations of A. catalpifolium in Emeishan and Dujiangyan were significantly different, there are 105 individuals in Emeishan population and 81 individuals in Dujiangyan population, the age class structure of the population was complete. The diameter class structure of A. catalpifolium showed a spindle-shaped structure with a large proportion of middle age grade and a smaller proportion of young age grade and old age grade. The dynamic change index of population age structure of A. catalpifolium showed that the population age structure dynamic index under random disturbance(V_pi')were 0.011 6 and 0.004 2, respectively, both of which were close to 0. It was showed that the populations were converting from decay-type to decline-type structure. According to the life table, the early death rate of A. catalpifolium was higher than other age, the survival rate were decreasing with age class increased, and the selection effect of the environment was strong. The survival curve were tend to Deevey-Ⅱ, and the mortality was similar in each age level. The survival function analysis showed that the survival rate function S(t) of the two populations presented a monotone decreasing trend with the increase age level, while the cumulative mortality rate F(t) presented a monotone increasing trend, and the changes of the two function curves were complementary. The time series predicted that the number of saplings decreased with old trees increasing gradually. It may difficult to remain the stability of the population for a long time after more trees grow in the 2, 4, 6, 8 age groups in the future. If the seedlings in the population are difficult to supplement, and saplings are not sufficient, the population of A. catalpifolium will become a declining population after 4 years of age.【Conclusion】The biological characteristics and human interference may be the key factors which had made A. catalpifolium endanger, the protection of the population and habitat of A. catalpifolium should be strengthened, the existing adult individuals of A. catalpifolium should be protected, promote the germination of seeds and the renewal of seedlings, and prevent the destruction of habitat and ecosystem. In order to improve germination rate and seedling formation rate of A. catalpifolium seeds, promote seedling conversion rate of A. catalpifolium seeds, the biological characteristics and breeding of A. catalpifolium should be further studied. In addition, artificial cultivation and other measures should be taken to strengthen the protection of individuals and habitats of middle and small diameter A. catalpifolium population in the regeneration of natural forest, so as to promote the natural regeneration and recovery of A. catalpifolium population.