米槠-木荷林优势种群的年龄结构及其更新策略

通过年轮分析,构建了浙江天童米槠-木荷林优势种木荷、米槠、石栎的年龄结构,分析了高生长和径向生长及萌枝策略随年龄的变化规律,探讨了干扰对群落动态的影响。研究结果表明:(1)3个物种的胸径、高度与年龄的关系均可用logistic曲线和线性模型拟合,但随年龄增加胸径、高度与年龄的关系显著下降。(2)随年龄增加3树种的DBH/H逐渐增加,米槠、石栎幼龄个体(1-20a)的有萌个体率和有萌个体萌枝数逐渐下降;米槠和石栎幼苗的主干较木荷细长、多萌枝,木荷和石栎成树主干较米槠细长;体现了米槠的更新策略具开拓性,木荷的具保守性,石栎在幼龄期具开拓性,成年期转为保守性。(3)米槠和石栎的年龄结构呈逆J型,幼龄个体充足,但中龄段(21-40a)存在更新断层,这与其高消耗的开拓性策略有关;木荷的年龄结构呈间歇型,各龄级均存有个体,这与其保守性策略有关;(4)3物种在大龄级上(52-60a)均存在更新高峰,与该地区的择伐干扰时间一致,高强度的干扰促生了次生演替,形成了以木荷为第一优势种的群落。(5)米槠、木荷、石栎的年龄结构是更新策略和干扰的综合表现,它不仅与径级结构一样可展现种群更新特征、预测种群发展动态,更能精确地反映群落动态事件的发生频次和发生时间。

Age structure and regeneration strategy of the dominant species in a Castanopsis carlesii-Schima superba forest

Evergreen broadleaved forests (EBLFs) is the zonal forest ecosystem of the subtropical zone in east China and have been degraded from intense recent anthropogenic disturbance. Studies of age structure of main tree species in EBLFs may provide an insight into their regeneration patterns and understand the role of disturbances in EBLFs, which are helpful to restoration of the degraded EBLFs. We constructed age structure of Schima superba, Castanopsis carlesii and Lithocarpus glaber which are the dominant species in an EBLF in Tiantong National Forest Park, Zhejiang Province, east China. All trees in two 20m×20m plot were collected and dendroecological technique was used to measure the age of individual taller than 1.5m, while the age of individual lower than 1.5 was determined by counting bud scale scars. The regression relationship between DBH/H and age were established and were used to calculate the age of individuals that can not be directly measured. The value of DBH/H was used to indicate the slender degree of trunk, meanwhile the percentage of multi-stemmed individuals in all individuals (PMSI) and the sprouts number of multi-stemmed individuals (NSMS) were used to indicate the sprouting ability. The trends of DBH/H, PMSI and NSMS with increasing age were compared among 3 species. The results were shown as follows: (1) The relationship between DBH/height and age could be well fitted by linear regression and logistic regression for three species, but these relationships collapsed with increasing age. (2) The value of DBH/H increased with age for three species and the value of PMSI and NSMS decreased with age at the young stage for Castanopsis carlesii and Lithocarpus glaber. The seedlings and saplings of Castanopsis carlesii and Lithocarpus glaber had more slender trunk and more sprouts than Schima superba, but the adults of Castanopsis carlesii had more thick truck than Schima superba and Lithocarpus glaber. It indicated that Castanopsis carlesii performed an exploiting regeneration strategy and Schima superba performed a conserved regeneration strategy in the whole life history, while Lithocarpus glaber changed the exploiting strategy in young stage into conserved strategy in mature stage. (3) The age structure of Castanopsis carlesii and Lithocarpus glaber exhibited an inverse-J type with plenitudinous recruitments, but there were a gap in the middle age class (21-40 year old) which was determined by its exploiting strategy with high exhaustion rate. The age structure of Schima superba exhibited a multimodal type with stead death rate, which was related to its conserved strategy. (4) There was a recruitment peak in the 52-60 year age class for three species, which was in accord with the time of documented selective-logging period. This intense disturbance led to secondary succession and created a high-light environment for abrupt recruitment of Schima superba. (5) All the results suggested that the age structure of each species was the synergy consequence of the regeneration strategy and historical disturbances. The age structure not only could be used to show the regeneration pattern and predict the dynamics progress as with the size distribution, but also could accurately reveal the frequency and timing of vital dynamics events.