桂西南岩溶山地优势植物种群动态及其对岩溶作用的影响

Dynamics of Dominant Population and Its Influence on Karstification in Southwest Guangxi,China

实现岩溶植被生态系统的恢复和重建,必须对岩溶植被演替规律及其动力机制进行研究。蚬木(Excen-trodendron hsienmu)林是桂西南岩溶山地特有的具代表性的原生性森林,采用"空间代替时间"的方法,对处于岩溶植被不同演替阶段的以蚬木种群为优势的岩溶植被进行调查研究,探讨岩溶动力系统对蚬木种群发生发育的影响。结果表明:在先锋群落中,种群缺少大径级个体,幼苗幼树占多数,存活曲线略为凸形且接近于直线,种群结构基本为初始增长型;蚬木种群随着群落的演替发展由初始增长型向增长型或稳定型变化;在顶极群落阶段,蚬木种群存活曲线为凹型或直线型,种群具备所有径级的个体,幼苗幼树所占比例高,大径级个体所占比例少,种群结构基本上为增长型或稳定型,但在蚬木种群不占优势的顶极群落中,种群缺少中间径级的个体,种群结构表现为间歇型,存活曲线为不连续型。随着岩溶植被的演替发育,表层岩溶泉水中的Ca2+、游离CO2、HCO3-随着植被的发育和演替而呈现增大的趋势,pH值、水永久硬度则逐渐下降,显示水质的改善。

In order to restore the vegetation in karst degradation areas, we should conduct research on vegetation succession and karst dynamic mechanism. The Excentrodendron hsienmu community is distributed in the primary forest of karst areas across the transitional zone of north tropic to south subtropic, southwestern Guangxi, southeastern Yunnan, and northern Vietnam, centering in Guangxi. In this paper the authors studied the population dynamics of Excentrodendron hsienmu in the process of vegetation succession and its effects on karstification dynamics of the environment based on seven field plots in Nonggan National Park of Guangxi, aiming to understand the interaction between the succession development in this seasonal rain forest and the karst base, hence to find methods to protect this endangered species and seek ways to restore the vegetations in degradation areas nearby. “Spatial replacing temporal” approach was employed in the authors＇ studies to analyze the E. hsienmu populatiofl structure and dynamics and try to prove the mutual action between the karst dynamic process and the vegetation development. The results show： ① In the pioneer communities where big individual trees were absent but saplings and seedlings were abundant, the survival curve was convex approximating to linear, the population structure was initially expanding, the trend of E. hsienmu population structure evolved from initial increase to expanding growth and then to stable balance. ② In climax communities where the number of individual plant appeared rationally within each size class with high proportion of seedling and sapling but less big trees, the survival curves were con- cave or linear but fractured, the population structure was expanding or stably balanced, but broken. ③ Strong karstification was correlated to developed root systems of mature vegetation; the epikarst spring water properties reflected the vegetation effect on karstification in which concentrations of free CO2, HCO3are questionable, but pH value, Ca2＋ and hardness of water decrease gradually in the process of vegetation development and succession, revealing the improvement of water quality.