神农架山地河岸带连香树的种群结构与动态

以种群统计学和树木年代学的方法, 从年龄结构、生命表、径向生长和干扰史4个方面, 研究了神农架山地河岸带连香树 (Cercidiphyllum japonicum) 的种群结构与动态。结果显示:1) 连香树种群内幼龄个体比较充足, 但在长时段内更新时有断代, 多个局域种群有明显可辨的同生群 (年龄幅宽约为50a), 其发生年代在20世纪20年代和70年代, 高峰期则在40年代和90年代;2) 萌枝更新非常突出, 与种群年龄和群落盖度有显著相关 (r>0.6, p<0.05) ;3) 经20a以下和60~100a间两个死亡高峰以后, 种群可达生活力最优阶段, 180a以后出现衰老迹象, 生存曲线总体上介于DeeveyⅡ和Ⅲ型之间;4) 前30a连香树胸径的生长速率最快, 经2次生长释放后, 约在60a前后进入林冠层, 90~120a间进入成熟期前, 胸径分化最为剧烈;5) 干扰高峰年 (20世纪20年代、70年代和90年代) 与种群更新的高峰年大致吻合。这些结果表明, 个体生长发育特征与中长期的干扰对其种群结构与动态有重要影响。由于幼苗尤其是萌枝的的数量充足, 连香树种群在中短期内可以维持。

POPULATION STRUCTURE AND DYNAMICS OF CERCIDIPHYLLUM JAPONICUM IN RIPARIAN ZONES OF THE SHENNONGJIA MOUNTAINOUS REGION, CENTRAL CHINA

Aims Cercidiphyllum japonicum, an endangered tree species confined to East Asia, grows mainly in the riparian zones of the Shennongjia mountainous region of central China. Our objectives were to explore regeneration and maintenance mechanisms of C. japonicum populations in montane riparian zones by examining age structures, life tables and radial growth processes, as well as disturbance history. Methods We surveyed four rivers in the Shennongjia mountainous region and placed 12 quadrats (ranging from 10 m × 20 m to 35 m × 60 m) in riparian zones with sizable C. japonicum populations. In each quadrat, diameter at breast height (DBH) (or basal diameter if tree height < 1.3 m) and height of each tree was recorded. For multi-stemmed trees, the largest stem was treated as the main stem and the rest as sprouts. Scattered C. japonicum occurring along our routes were also recorded. Cores were extracted from 60 large C. japonicum stems at 1.3 m height and basal discs were taken from 10 young stems at slightly >1.3 m for dendrochronological procedures and subsequent DBH-age regression. Increment sequences >40 years were used for detection of release-events based on a percentage growth change filter. Important findings DBH of C. japonicum grew consistently rapidly in the first 30 years. There were two release events before canopy accession at about 60 years. Differentiation in DBH and height took place at 90–120 years. After two mortality peaks in ≤20 and 60–100 years, C. japonicum approached and sustained optimum vitality up to 180 years when senescence occurred. Its survivorship curve was generally between Deevey type II and III. Young individuals were abundant. Regeneration, however, was discrete over long intervals. Cohorts with an age range of about 50 years that established in the 1920s and 1970s and culminated in the 1940s and 1990s were remarkably discernable in most local populations. Regeneration by sprouting was predominant and strongly correlated with stand age and community cover. Dates of heavy disturbances (1920s, 1970s and 1990s) roughly corresponded with dates of population recruitment pulses. We suggest that individual growth and developmental characteristics and moderate-to-long-interval disturbances played important roles in driving C. japonicum population dynamics. For short to moderately long periods, C. japonicum can maintain its population due to adequate young individuals, especially sprouts.