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Spatio-temporal dynamics of two alpine treeline ecotones and ecological characteristics of their dominate species at the eastern margin of Qinghai-Xizang Plateau
ZHOU Tian-Yang, NARAYAN Prasad Gaire, LIAO Li-Bin, ZHENG Li-Li, WANG Jin-Niu, SUN Jian, WEI Yan-Qiang, XIE Yu, WU Yan
Chin J Plant Ecol    2018, 42 (11): 1082-1093.   DOI: 10.17521/cjpe.2018.0082
Abstract   (1213 HTML159 PDF(pc) (3410KB)(1486)  

Aims Temperature limit is the main cause of alpine treeline formation. Therefore, it is important to understand the response mechanisms of alpine treeline as well as their tree species under the global climate change. The present study focused on the spatio-temporal dynamics of treeline and ecological characteristics of the tree species in two treeline ecotones.
Methods Two vertical belt-transect plots were established in each treeline ecotone of the Zheduo Mountain and Jianziwan Mountain of the eastern Qinghai-Xizang Plateau. Top and bottom of each transects were lain between species line and forest line, respectively. Detailed information of each tree species treeline, including species name, latitude, longitude, height, age, base diameter, and coordinates, was recorded accordingly.
Important findings The temperatures of the two research areas have increased during the past 58 years. The precipitation has decreased slightly in both the Zheduo Mountain and Jianziwan Mountain. The age structure of Abies fabri from the Zheduo Mountain and A. squamata from the Jianziwan Mountain showed a reversed “J” shape curve and a bimodal shape, respectively. Within the two transects, due to the limitation of seed diffusion, the dominate species showed aggregated distributions at the small scale. At the large scale, A. fabri was aggregated at the Zheduo Mountain, while A. squanmata of the Jianziwan Mountain was randomly distributed due to the impact of surrounding environmental factors. Both tree height and base diameter decreased with the increase of elevation. The fir trees (Abies spp.) at the upper part of the treeline ecotone presented an allometric growth, whose height growth rate was higher than that of base growth, while the relationships between height growth and base growth were isometric at almost mid and lower part of the treeline ecotone. Compared with 10 years ago, there was no significant change at the position of treeline and tree species line of the Zheduo Mountain and the Jianziwan Mountain, neither of the tree density in the Jianziwan Mountain. However, the number of trees in the Zheduo Mountain increased by about 25%. Compared with 20 years ago, tree species lines of the Zheduo Mountain and Jianziwan Mountain were shifted upwards by 50 and 30 m, respectively. Besides, their treeline positions were increased by 75 and 40 m, respectively. Furthermore, the number of trees also increased significantly by 220% and 100%, respectively. Therefore, the treeline and its constructive species are mainly affected by temperature at the large spatio-temporal scale, while influenced by temperature and ambient environment at the small spatio-temporal scale.


Fig. 4 Point pattern analyses for the Zheduo Mountain (A) and Jianziwan Mountain (B). The two green lines are the confidence intervals for the fitting, and the solid line is from the simulation.
Extracts from the Article
对两个样地的建群种冷杉进行点空间格局分析, 结果见图4。研究表明样地间的分布格局有明显的差异, 折多山样地的峨眉冷杉在小尺度范围内呈聚集分布, 随着尺度的增加, 聚集程度有所提高; 剪子弯山样地的鳞皮冷杉在小尺度范围内同样呈现聚集分布, 小于60 m的范围内聚集程度呈现波动状态, 在更大的尺度上(>60 m)则呈现出随机分布格局, 表明其分布格局与尺度大小密切相关。
利用树高与树龄间的关系对样地树线分布进行模拟分析(10年前及20年前), 具体树高-树龄模型见表3。建立的两个样地的树高-树龄模型均较好(p < 0.001, R2分别为0.68和0.71), 能较准确地模拟前10至20年的情况。模拟结果见图5, 由模拟分布图可以看出, 目前折多山样地的树线海拔约为4 275 m, 树种线海拔约为4 380 m, 样地最下端为郁闭森林; 与10年前相比, 目前该样地的树线及树种线位置无明显变化, 而树木数量提高了约25%; 20年前树线及树种线的海拔分别约为4 200 m和4 330 m, 与目前相比, 二者分别提高了75 m和50 m, 而树木个体数(54株)仅为目前的1/3。剪子弯山样地目前的树种线位于海拔4 520 m处, 树线位于海拔约4 440 m处; 10年前该样地的树木个体数、树线及树种线位置与目前基本保持一致; 20年前树木个体数(47株)仅为目前的一半, 树种线位于4 490 m处, 而树线位于样地下方具体海拔无法确定, 相比当前样地内树种线上升了30 m, 树线位置至少爬升了40 m。
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