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题名: 横断山区亚高山森林格局动态及其对气候变化的响应
作者: 石松林1
学位类别: 博士
答辩日期: 2017-05
授予单位: 中国科学院大学
授予地点: 北京
导师: 刘国华
关键词: 高山树线 ; 森林生长 ; alpine tree-line, forest growth, Dendrochronology, climate change, Wolong National Nature Reserve ; 树轮生态学 ; 气候变化 ; 卧龙国家级自然保护区
其他题名: Dynamics of subalpine forest in response to climate change on the Hengduan mountains
学位专业: 生态学
中文摘要: 西南横断山区亚高山分布着大量的原始森林,其森林类型多样,是世界上针 叶树种最为丰富的地区之一;因其独特的地理环境而较少受到人为活动的干扰, 是研究自然条件下森林动态对全球气候变化响应的理想区域。近几十年来,该区 域经历了明显的变暖趋势,特别是高海拔区域,升温速率更快,可能会对森林产 生影响;然而,我们对亚高山森林生长和群落时空动态对气候变化的响应关注较 少。本文采用树木年轮学和群落生态学相结合的方法,从样地、局地和区域尺度 上揭示了亚高山森林动态对气候变化的响应。在样地尺度上,以一条完整的岷江 冷杉(Abies faxoniana)林 30米×1910米的样带(从河谷到树线)为例,揭示了 过去 200年以来群落结构动态和各优势种群分布范围沿海拔变化历史及其对气 候变化的响应特征;以 3个 40米×300米的不同坡向(NW、NE和 SE)的树线交 错带样地为例,揭示了过去 200年以来树线群落结构动态、树线位置和各优势种 群物种线位置的变化历史及其对气候变化的响应特征。在局地尺度上,以卧龙地 区主要的亚高山森林为对象,评估了物种、海拔、地形和树龄等非气候因素对气 候—树木生长之间关系的影响。在区域尺度上,揭示了整个区域亚高山针叶林生 长时空动态格局及其对气候变化的响应机制。主要结论如下: 1、自 1980s以来,横断山亚高山区域经历了显著的变暖趋势,年平均气温、 年平均最低温度和年平均最高温度的上升速率分别为 0.400、0.399和 0.555℃/10a, 而降雨无明显的变化趋势。低、中、高海拔区域的增温速率分别为 0.540、0.391 和 0.376℃/10a;呈现出明显的海拔分异格局。 2、在过去 200年以来,海拔梯度(海拔 2970-3824米)上岷江冷杉林群落 结构与组成发了显著变化,其中岷江冷杉种群分布范围基本保持稳定,而林下的 糙皮桦(Betula utilis)、大叶金顶杜鹃(Rhododendron faberi subsp. pratti)、无柄 杜鹃(Rhododendron watsonii)和绒毛杜鹃(Rhododendron pachytrichum)等种群 分布范围均发生了显著扩张现象,其中最为明显的是糙皮桦种群。 3、过去 200年以来,三个不同坡向(NW、NE和 SE)的树线位置均发生了 显著变化,其中变化最为明显的是 NE坡,暗示了树线位置向上爬升的速度与坡 向有明显的关系。只有 NE样地内的岷江种群分布范围表现出显著扩张的现象, 而其它两个坡向的样地物种线位置基本保持稳定。相比岷江冷杉种群,其林下的 糙皮桦、西南花楸(Sorbus rehderiana)、微毛樱桃(Cerasus clarofolia)和大叶金 顶杜鹃等种群的物种线位置发生了更为迅速的移动,其中变化最为显著的是糙皮 桦种群。 4、自 1980s以来,样带内各海拔以及三个树线样地内的岷江冷杉更新均出 现显著增加的现象,均与温度呈显著正相关,揭示气候变暖可能是驱动种群密度 增加的主要因子。然而,各海拔岷江冷杉更新的数量却呈现较为明显的差别,高 海拔区域(3600-3800米)更新数量显著高于其它海拔区域,暗示了群落内种间、 种内关系等生物因子及其它非气候因子也会对更新产生一定的影响。 5、森林生长对气候变化的响应存在着较为明显的物种、海拔、地形和林龄 差异;针叶树种比落叶阔叶树种对气候变化的响应更为敏感;随着海拔的升高, 岷江冷杉林的生长对气候变化的响应敏感性逐渐增加;阴坡比阳坡的岷江冷杉林 对气候变化的响应更为敏感;林龄较大比较小的森林生长对气候变化的响应更为 敏感。 6、气候变暖驱动着横断山区亚高山针叶林生长加速;对气候变化响应高敏 感性与高海拔区域较高的增温速率是引起高海拔比低海拔区域针叶林生长速率 更快的主要原因。
英文摘要: The north-south oriented Hengduan Mountains, situated in the southwestern China, is covered by widespread primeval forest including abundant tree species, and is one of the diverse conifer species regions in the world. Subalpine forest is well preserved in the nature reserve and remains relatively undisturbed by human due to the complex topography, making this region as a potential ideal place for examining the dynamics of forest in response to climate change. Meanwhile, this region has experienced greater warming rates, particularly at higher elevations, and showed a pattern of elevation- dependent warming, which can have an impact on forest ecosystems. Yet, little is known regarding how climate change influences the temporal and spatial dynamics of subalpine forest growth and community. Here, we used dendrochronological techniques and method of community ecology to assess how climate change has affected the dynamics of subalpine forest at plot, local and regional scale. At the plot scale, the dynamics of forest composition and range shifts of dominant tree species along an altitudinal transects in response to climate change were detected based on a plot (30m×1910m) of Abies faxoniana from a river valley to tree-line. Simultaneously, three tree-line plots (40m×300m) were established in the Wolong Nature Reserve toward the northwest, northeast and southeast, respectively, which could be used to identify spatiotemporal variation of forest, shifts of tree-line position and distribution of dominant tree species across elevation. At the local scale, our research showed that species, elevation, topography and age could have an effect on climate-growth associations. Consequently, this study revealed patterns and mechanisms of coniferous forest growth in subtropical alpine mountain ecosystems in response to climate change at the regional scale. We concluded that: 1. Temperature exhibited a significantly increasing trend, with a rate of 0.400, 0.399, and 0.555 °C/decade in annual mean, minimum and maximum temperature, whereas precipitation showed non-significant changes after the early 1980s. Meanwhile, this region has experienced greater warming rates at higher elevations and showed a pattern of elevation-dependent warming. The warm rate is 0.540, 0.391, and 0.376 °C/decade in the high, medium and low elevational regions, respectively. 2. The forest composition and distribution of A. faxoniana had changed significantly along an altitudinal gradient from 2970m to 3824m in the past 200 year. Although distinct boundary of Abies faxoniana had only moved insignificantly across elevation, a significant range shift had occurred in the tree species including Betula utilis, Rhododendron faberi subsp. pratti, Rhododendron watsonii and Rhododendron pachytrichum. Betula utilis indicated more rapid upslope shift that other tree species. 3. Over the past two centuries, the tree-line position of three plots toward different aspects (NW, NE and SE) showed significant, but inconsistent upward movement in response to climate change, and most rapid upward shift occurred in the location of northeastern forest, implying that range shifts of the tree-line positon could be strongly related to topographical aspect. A significant upslope shift of Abies faxoniana only appeared in the northeastern forest. However, Betula utilis, Sorbus rehderiana, Cerasus clarofolia and Rhododendron faberi subsp. pratti moved rapidly and significantly upslope along elevation gradients and B. utilis had most rapid upslope shift. 4. A significant and increasing number of seedlings and density had occurred in the three tree-line plots and one elevation transect after the 1980s. Significant and positive correlation between recruitment of Abies faxoniana and temperature suggested that climate warming played a prominent role in increasing population density. Although there was similar pattern of regeneration along an elevation transect, the high altitude areas had more recruitment than the low altitude areas, implying that intraspecific and interspecific relationship, and environmental factors could have an influence in regeneration. 5. Our results showed that there could be the apparent variability of climate— growth among the forests at different tree species, elevations, topographical aspects and ages. Conifers were more sensitive to climate change than deciduous broad-leaved tree species. It had the increasing sensitivity of tree growth in response to climate change across the elevation gradient. Meanwhile, forest growth on north-facing aspect had stronger sensitivity to climate than that on south-facing aspect. In addition, old trees responded more strongly to climate than young trees. 6. Climate warming plays a prominent role in an unprecedented acceleration of alpine conifers growth in the Hengduan Mountains in recent decades. Our result indicated that both strong forest sensitivity to temperature and high warming rates could result in greater forest growth speed at high elevations than low elevations.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/38689
Appears in Collections:城市与区域生态国家重点实验室_学位论文

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作者单位: 1.中国科学院生态环境研究中心
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