【作者】 王婷；

【导师】 马克平； 于丹；

【作者基本信息】 武汉大学 ， 植物学， 2004， 博士

【摘要】 树木的生长和立地环境密切相关并受多种气候因子的影响。一方面，大多数树木年轮的宽窄能够真实地记录下过去的气候变化，树木年轮资料可以用来重建过去几百年甚至上千年气候变化的代用资料；另一方面，一些有关林线动态的研究也证明林线种群的年龄结构也是表示气候变化的指示因子之一。本文应用种群生态学和树木年代学的方法并结合气象资料，研究了中部天山不同海拔高度上天山云杉(Picea schrenkiana)种群的年龄结构以及树木年轮宽度与气候变化的关系。主要结果归纳如下： 1)．分上、中、下三个海拔梯度研究了中部天山云杉林的年龄结构和种群动态沿海拔梯度的变化情况。森林下限接近干旱沙漠地带，土壤含水量低，温度比较高且降水量少，降水量可能是影响森林下限天山云杉生长和更新的主要的限制因子；在中海拔林区幼苗和幼树比较多，林内的个体间的竞争引起的自疏作用可能是限制林下更新主要原因；森林上限的天山云杉大多比较老，＜60a的天山云杉个体数目仅占上限云杉个体总数的14％；影响幼苗成活的原因如温度等可能是限制高海拔森林上限种群更新的主要原因。 2)．分三个不同的海拔梯度研究天山云杉年轮宽度与气候变化的关系，即低海拔森林下限(1600～1700 m a.s.l.)，中海拔内部林区(2100～2200 m a.s.l.)．高海拔森林上限(2600～2700 m a.s.l.)。研究证明不同海拔高度天山云杉的径向生长都与当年生长季及上年生长季末期的温度负相关，都与降水显著正相关；随着的海拔的降低，月均温升高，降水的重要性也随之加强，低海拔森林下限是树木生长对气候变化的“干旱敏感地带”；海拔越高，树木生长受上一年降水影响作用越大。 3)．不同年龄的天山云杉对气候变化的反应特征不相同：幼龄树木对当年生长季的温度和降水的响应比较敏感，而老龄树木则对生长季前期及上年生长季末期的气候变化比较敏感;年表所包含的样本的年龄组不同，其对气候变化的响应特征也不同;年表所包含的样本的年龄跨度大，则容易模糊不同年龄树木对外界气候变化反应的特性。 4).气象资料和树木年代学研究结果都证明天山中部近几十年来的温度有所升高，但高海拔林线处近几十年来的幼苗和幼树更新反而有所下降;林线处树木年轮宽度主要和2月份温度正相关，而幼苗的存活则主要受年内或年际间的温度变化的影响比较大。较高的温度不是引起高海拔林线上升的唯一的气候因素;如果年季间的温度波动比较大，即使全球气温继续变暖，高海拔林线也会因更新不良而不会有所明显的上升。在未来的几十年内，如果中部天山高山林线地带的更新状况不能得到改变，林线将会在较长时间内保持稳定状态或稍有下降。 5).天山云杉种群的存活曲线基本介于Dee\’e yH和Deet’eyIIl型之间，其幼苗和幼树的因竞争光、水分和养分等而死亡率较高。70a以前的死亡率很高.但从7Oa~1 40a之间天山云杉基本上进入稳定阶段，1 40a左右开始出现成熟后死亡。中部天山上倒一J型的年龄结构分布曲线，以及随年龄增长而降低的密度和生物量变化趋势，和基本介于DeeveyH和Deeve}’I11型之间的存活曲线.都表明中部天山的天山云衫种群处于稳定发展和更新的时期。更多还原

【Abstract】 Relationships between tree growth and environment are complicated. One hand, tree rings could provide reliable records of past climatic conditions, tree ring chronologies are therefore the most widely used proxy for reconstructing annual variations in climate that extend back several centuries to millennia. On the other hand, population structures in the treeline ecotones are also found to be good indicators of climate change by many studies on treeline dynamics. By using phytopopulological and dendroecological methods, this paper has studied the correlation between climate change and the age structure or tree-ring width from different altitudinal ecotones. Primary results of this paper were summarized as following:1). To study the size distribution and age structure, the Picea schrenkianu (Fisch. et Mey.) forest of the central Tianshan Mountains was divided into three transects, i.e.. lower limit (1500-1700m). mid-altitude (1800-2400m) and upper treeline (2500-2700m). A reverse-J shape age structure was found in the mid-altitude transect, self-thinning and density dependent competition between trees was probably the most important influence factor in this ecotone. The low altitude transect was characterized by the dominance of young trees, precipitation may be the important factor to survival and population age structure of P. schrenkiana forest in this transect. However, a bell shape age structure was found with infrequent recruitments and the <60a age class accounted for 14% of total individuals in the cold high altitudinal treeline. Low temperature may be the major limiting factor to population dynamics of this high altitudinal ecotone.2). Three chronologies were developed at three different altitudes, i.e., lowforest border (1600-1700m a.s.l.), interior forest (2100-2200m a.s.l.). and upper treeline (2600-2700m a.s.l.). to study the correlation between tree-ring width and climatic change. Trends in annual ring-width variations were similar among the three sites but variability was greatest at the low forest border site. The results showed that tree radial growth positively correlated with precipitation but negatively with temperature even at the cold high-elevation treeline site. With decreasing altitude, air temperature increased and the importance of precipitation on tree growth increased. Trees most sensitive to drought were found near the arid low forest border. Precipitation during the growing season also influenced tree-ring growth patterns, but the lag effect was the dominant limiting factor at sites of higher elevation.3). P. schrenkiana from the treeline of central Tianshan Mountains were disaggregated into different age class to discuss the relationships between tree-ring width and climate by using correlation coefficients and response function. The results suggested that the radial growth of young P. schrenkiana were significantly correlated with temperature and precipitation from the current growth period: but the tree-ring width from the aging trees were more influenced by the climate of the end of previous growth period or by the temperature and precipitation prior to current growth period. Chronologies responsed to climate differently if they concluded different age-class tree ring cores. The wider age class of age-independent tree ring models one chronology contains, the less accurate reconstructions of past climate this chronology could give.4). Both the climatic records and dendroecological data confirmed climatic warming in recent several decades in the central Tianshan Mountains, but the regeneration has decreased in the recent several decades. Tree radial growth was positively correlated with mean February temperature, whereas reproduction and establishment of seedlings were mainly influenced by climatic fluctuation of intra-year or interannual temperature. High temperature is not the only factor to cause treeline rising, it could not rise even with global warming if climatic fluctuation of intra-year or interannual temperature increased. It is inferred that if the regeneration更多还原