气候变暖对老秃顶子林线结构特征的影响

The effect of climate warming on the structure characteristic of the timberline in Laotudingzi Mountain

运用样带样方法和年轮气候学方法对大海林地区的气候因子和样地数据进行了分析。结果表明 ,近 30 a来老秃顶子地区气候变暖明显 ,尤其是冬季增温最明显 ,月份增温中以 2月份最大 ;寒冷时期 (12月份、翌年 1和 2月份 )和温暖时期 (6～ 9月份 )的温度都有增加 ,但是寒冷时期温度的增加幅度较大 ;冬季与夏季温差稍有减少 ,但积温有所增加 ,整年的热量正在增加。全球变暖导致的大海林地区增温对老秃顶子林线结构特征产生了很大的影响 ,由样地调查和分析可知 ,全球变暖导致林线中上部幼苗、幼树的更新和存活增多 ,森林密度加大 ,树木平均年龄降低 ,年龄结构呈倒 J字型 ,并且多呈聚集分布 ;而在林线的下部 ,幼苗更新很少 ,主要以中龄林存在 ,并且多呈零散分布形式。通过年轮分析得出 ,气候变暖导致林线树木径生长和高生长增加 ,而且增加的趋势和近 30 a来温度的变化基本一致。通过对年轮指数与气候因子的相关性分析 ,表明林线树木年轮指数与温度的相关性较强 ,而与降水的相关性较弱 ,并且年轮指数与温暖时期温度和积温呈正相关 ,而与寒冷时期温度和年平均温度呈负相关 ,表明温暖时期温度和积温控制着林线的海拔高度 ,而寒冷时期的温度和年平均温度主要对林线树种类型起着决定性的作用。从敏感度分析看出 。

Ecotones, the boundary zones between major ecosystems, are important sites for examining the effects of climate change on ecosystem structure. The forest-tundra ecotone, formed by alpine timberline, may be especially sensitive to climate change. This paper analyzed the timberline stand structure related climate factors at Laotudingzi Mountain in Dahailin region by using transect investigation and dendrochronological methods. There was a trend of climate warming during the past 30 years, especially in winter seasons. February was the most sensitive month in a year. Both summer and winter temperature increased, and the later was greater. The temperature difference between summer and winter decreased, but the accumulated temperature slightly increased, indicating that the yearly heat increased. The climate warming in Dahailin region greatly influenced the structure characteristic of the timberline. The rate of regeneration and survival in the upper timberline ecotone and forest coverage increase, but stand age decreased. The trees class was clumped distributed structure with and an inversed 'J' type age structive. The regeneration in the lower timberline was poor and exhibits scattered distributed. The diameter and height growth increased because of the climate warming. The trend of the ring index was consistent with the temperature variation during the past 30 years. The tree ring index at timberline was strongly correlated to the temperature and slightly to precipitation. The warm period temperature and accumulated temperature were positively correlated to the ring index, while the cold period temperature and mean annul temperature were negatively correlated to the ring index. These suggested that the warm period temperature control the timberline elevation, and the cold period temperature determine the type of tree species at timberline. The sensitivity analysis indicated that the tree at the upper timberline was more sensitive than those at lower timberline, but not at the most upper timberline. The sensitivity of Betula ermanii was better than spruce-fir by comparing, which mainly related with the location of Betula ermanii, and the mid-age tree had the better sensitivity.