中文摘要：

为预测气候变化下的森林植被生长季特征变化,本文基于华北晋冀山地区和黄土高原区两个区域44个气象站1961-2013年日气温数据,分析了华北湿润半湿润地区两个区域树木生长季特征的变化趋势。定义生长季开始时间为当连续5天日平均温度≥5℃,选第5天作为生长季开始时间;生长季结束时间为当秋季连续5天日平均温度〈5℃,选第5天作为生长季结束时间。结果表明：①1961-2013年晋冀山地区和黄土高原区以及两个区域整体树木生长季开始时间呈现显著提前趋势,变化速率分别为-1.7d/10a、-2.1d/10a和-1.9d/10a;树木生长季结束时间均呈现显著延后趋势（p〈0.05）,变化速率分别为0.9d/10a、1.1d/10a和1.0d/10a;研究区树木生长季长度表现出明显的延长趋势,晋冀山地区和黄土高原区以及两个区域整体的树木生长季长度时间变化速率分别为2.6d/10a、3.2d/10a和2.9d/10a,树木生长季长度分别延长13.3d、16.4d和14.8d;②1961-2013年,海拔对树木生长季指标的影响,除了对晋冀山地区的树木生长季开始影响不大以外,对于两个研究区的其他树木生长季指标均有显著影响;研究区树木生长季指标（生长季开始时间,结束时间和生长季长度）与春季和秋季气温都显著相关;③1961-2013年,树木生长季开始时间变化趋势在整个研究区空间上大部分呈提前趋势,树木生长季结束时间大部分呈延后趋势和树木生长季长度的变化趋势在空间上则大部分呈延长趋势。

英文摘要：

Based on daily mean temperature measurements at 44 meteorological stations throughout the Hebei Shanxi mountainous region and Loess Plateau region,Northern China from1961 to 2013,trends in the tree growing season were analyzed in two regions（humid and subhumid）. The growing season was defined as the last day of the first 5- day period with a daily mean temperature greater than 5 ℃ to the last day of the first 5- day period with a mean temperature of less than 5 ℃. We found that over the last 50 years,the commencement of the tree growing season has increased at a rate of-1.7d/10 a,-2.1d/10 and-1.9d/10 a,throughout the Hebei Shanxi mountainous region,Loess Plateau region and the whole study area,respectively. The end of the tree growing season has decreased at a rate of 0.9d/10 a,1.1d/10 a and 1.0d/10 a in the three areas,respectively. The length of the tree growing season in the study area increased from 1961 to2013 at a rate of 2.6d/10a（13.3 days）,3.1d/10a（16.4 days）and 2.9d/10a（14.8 days）in the three study areas respectively. Elevation had a strong impact on the tree growing season indices（growing season start,end and length）,except for a little effect on commencement of the tree growing season in the Hebei Shanxi mountainous region. Tree growing season indices（start,end and length of the growing season）were associated with spring and autumn temperatures. The spatial distribution of the trend in the commencement of the tree growing season showed a decreasing trend. The end point and length of the tree growing season has increased.