山体效应对北半球林线分布的影响分析

Mass Elevation Effect and Its Contribution to the Altitude of Timberline in the Northern Hemisphere

通过搜集整理了北半球516个林线数据,结合WorldClim气象数据计算了林线数据点上的大陆度,并依据SRTM高程数据提取了林线处的山体基面高度(作为山体效应的代用因子),然后以纬度、大陆度和山体基面高度为解释变量,建立三元回归模型。结果表明:线性回归模型的判定系数R2为0.904,二次回归模型的R2高达0.912。相比先前不考虑基面高度的林线分布模型(R2=0.79),纳入了山体基面高度的林线分布模型能够更加有效的拟合半球尺度的林线分布;结果还表明,山体基面高度对北半球林线高度分布的贡献率达到了48.94%(p=0.000),而纬度和大陆度分别为45.02%(p=0.000)和6.04%(p=0.000)。这揭示了山体效应对半球尺度林线分布具有重要的影响。基面高度在北美洲地区对林线高度的贡献率最大(50.49%,p=0.000),在欧亚大陆东部地区为48.73%(p=0.000),在欧亚大陆西部地区为43.6%(p=0.000)。这一结果说明山体效应对林线分布高度的影响虽有区域差异,但都有较高的贡献率。

Alpine timberline, as the ＂ecological transition zone,＂ has long attracted attention of scientists in many fields of study, especially scientists of climatic change in recent years. Many unitary and dibasic fitting models have been developed between timberline and its influencing factors. It has been commonly believed that latitude or temperature is a decisive factor for the altitudinal distribution of timberline, and most of the fitting models involve the relationship between timberline and latitude or temperature. However, these models are usually on regional scale and could not be extended to other regions; on the other hand, hemispherical-scale and continental-scale models usually contain only about 100 timberline data and results in low precision. The present article has collected 516 data points of timberline, and takes latitude, continentality and mass elevation effect as independent variables and timberline elevation as dependent variables to set up a ternary linear regression model. Continentality is calculated using the meteorological data released by WorldClim and mountain base elevation （as alternative factor of the mass elevation effect） is extracted on the basis of SRTM 90-meter resolution elevation data. The results show that the coefficient of determination （R2） of the linear model is as high as 0.904, and that the contribution rate of latitude, continentality and mass elevation effect to timberline elevation is 45.02% （p = 0.000）, 6.04% （p = 0.000） and 48.94% （p = 0.000）, respectively. This revealed that the influence of mountain mass elevation effect on timberline distribution exceeds that of latitude and continentality put together, and that mass mountain effect is the primary factor in determining the elevation distribution of timberline on continental and hemispherical scale. The contribution rate of the mass elevation effect to the timberlines is, although different in different regions, generally high, e.g., 50.49% （p = 0.000） in North America, 48.73% （p = 0.000） in the eastern Eurasia, and 43.6% （p = 0.000） in the western Eurasia.