中国高山林线的分布高度与气候的关系

Geographical Differences in Alpine Timberline and Its Climatic Interpretation in China

通过研究我国高山林线的分布高度沿纬度、经度的变化格局,和对高山林线处的温度和基带降水等气候指标的分析,对我国高山林线分布高度与气候因子的关系进行探讨。结果表明:(1)我国高山林线高度表现出明显的纬向和经向变化,总体趋势是:在北纬30o以北,高山林线高度随纬度升高而下降,下降速率为112m/度左右;在30oN以南,则表现出较大的东西部差异:在东部,高山林线高度变化不明显,西部则随纬度增加呈上升趋势。在相似的纬度上,高山林线高度呈现出从东向西升高的趋势。高山林线在藏东南的洛隆、丁青、工布江达一带(约29o^32oN,94o^96oE)达到4600m,为世界最高林线高度,并以此为中心向四周降低。(2)影响高山林线高度的主导气候因子为生长季温度条件。我国高山林线高度的温度指标为年生物温度3.5oC,温暖指数14.2oC·月,生长季平均温度8.2oC。该指标相应海拔高度的地理差异,导致了我国高山林线高度的纬向、经向变化,和从沿海到内陆林线高度的差异。(3)降水对高山林线高度有显著影响。在中高纬度地区,相同纬度上干旱区域的高山林线高于较湿润区域,降水量是通过温度间接作用于林线高度的。

The variations of alpine timberline altitude with latitude and longitude in China were investigated and their relationships with climatic indices were analyzed in this study. The results are summarized as follows: (1) The altitude of alpine timberline in China changes significantly along latitudinal and longitudinal gradients. North of 30oN, the timberline altitude decreases with the increase of latitude at the rate of 112 m per latitude degree. South of 30oN, the latitudinal change shows a different pattern: the altitude does not vary significantly with latitude in the eastern part and increases with latitude in the western part. The timberline altitude drops with the increasing of longitude at similar latitudes, resulting from increased temperature conditions from east to west due to large-scale topographic and geographic factors. The highest timberline (4600 m) was observed in southeast Tibet (29o-32oN, 94o-96oN), the highest timberline in the world. (2) The timberline is limited by growing season temperature, i.e. Annual Biotemperature (ABT) of 3.5oC, Warmth Index (WI) of 14.2 oC·month, and Mean Temperature for Growing Season (MTGS) of 8.2 oC. The corresponding altitudes of these temperature thresholds change with geographic factors, and this change has led to the changes in the latitudinal and longitudinal timberline patterns and timberline variations from the oceanic to continental climate. (3) Precipitation affects obviously timberline altitude at the middle-high latitudes in China; timberline is higher in arid regions than in humid areas at the similar latitudes, caused by increase of temperature at the low humid conditions.