长白山北坡岳桦林线变动的水热条件分析

Water and Heat Changes of Betula ermanii Treeline on Northern Slope of Changbai Mountains

近50年来长白山北坡林线种群呈现明显的扩张态势。为揭示林线变动机制，本文以长白山天池气象站的气象数据（1953—2007年）为基础，结合野外的气温观测，以温暖指数（WI）及湿润指数（HI）为生态气候指标，以16℃·月和68．8mm／℃·月为阈值，通过数据保证率的计算推测55年来长白山北坡岳桦林线的水热条件变化。结果表明：以盯和Ⅲ指标确定的林线位置分别在1975～2460m和1584～2231 m。WI与Ⅲ变化对林线高度变动影响的交互作用不显著佃〉0．05），WI与肼变化呈显著负相关p〈0．01），两种林线变化也呈负相关（r=-0．11〈0），交互作用和相关分析结果显示水热条件的不同步变化使岳桦林线上侵不能达到各自的潜在高度，林线位置波动在1975～2231m。林线上缘波动的复杂程度高于下缘，波动幅度与胁迫力的大小呈正相关。

The treeline of Betula ermanii population had an obviously expanding trend on the northern slope of the Changbai Mountains in recent 50 years. In order to examine the changing mechanism of treeline, in this study, based on the data from Tianchi meteorological station （2624 m altitude） regarded as a referencing site （1953-2007） and the air temperature field measurement, using two eco-climatic preferences which were warmth index （WI） and humid in- dex （HI）, the ecotone boundary between Betula ermanii and tundra on the northern slope of the Changbai Mountains was determined by assurance ratio. The results were calculated by using the thresholds at 16 ~C. month and 68.8 mm/~C~ month, and they showed that the two treelines were at 1975-2460 m and 1584-2231 m respectively. The inter- action influence of WI and HI changes on treeline was not significant （p〉0.05）. There was a significant negative corre- lation between WI and HI change （p〈0.01）. In addition, there was a negative correlation between two treelines chang- es （r =-0.11〈0）. The results of correlation and interaction analysis indicated that the two treelines were unable to reach their potential height due to the asynchronous changes of heat and water. Therefore, the range of Betula ermanii treeline was estimated to be 1975-2231 m. The wavelike rise in Betula ermanii treeline （slope was positive, R2 〈0.8） was discussed by trend and wavelet analyses. The fluctuation process was simple in lower treeline （the characteristic of catastrophe point）. However, the complex fluctuation process in upper treeline indicated that fluctuation of treeline shift increased owing to large stresses.