中文摘要：

中国温带季风区是我国重要的农业区，春季霜冻常对该地区的植物造成严重的损害。本文利用“中国物候观测网”12个站点的物候观测数据和对应站点气象资料，应用物候模型方法，对1963—2009年各站点的霜冻频次和多种木本植物的始花期进行了分析，并对植物在花期的霜冻风险进行了评估。结果表明，1963-2009年，研究区内东北地区和华北地区的始花期分别以-1．52天／10a（P〈0．01）和-2．22天／10a（P〈0．01）的速度提前。在同一时段，研究区春季霜冻日数显著减少，终霜冻日显著提前。综合考虑花期和霜冻频次的变化，霜冻风险指数，即木本植物花期受到霜冻的物种数占调查总数的百分比，在东北地区以-0．37％／10a的速度降低（不显著）；而在华北地区，霜冻风险指数则以-1．80％／10a的速度显著下降（P〈0．01）。这表明过去半个世纪研究区植物花期霜冻风险在降低，且存在显著的区域差异。该结论可为农业和森林管理者制订应对春季霜冻害的决策提供参考。

英文摘要：

The temperate monsoon area of China is an important agricultural region but late spring frosts have frequently caused great damage to plants there. Based on phenological data derived from the Chinese Phenological Observation Network （CPON）, corresponding meteorological data from 12 study sites and phenological modeling, changes in flowering times of multiple woody plants and the frequency of frost occurrence were analyzed. Through these analyses, frost risk during the flowering period at each site was estimated. Results of these estimates suggested that first flowering dates （FFD） in the study area advanced significantly from 1963 to 2009 at average rates of-1.52 days decade-1 in Northeast China （P 〈 0.01） and -2.22 days decade-1 （P 〈 0.01） in North China. During this same period, the number of frost days in spring decreased and the last frost days （LFD） advanced across the study area. Considering both flowering phenology and occurrence of frost, the frost risk index, which measures the percentage of species exposed to frost during the flowering period in spring, showed a decreasing trend of-0.37% decade-~ （insignificant） in Northeast China and-1.80% decade-1 （P 〈 0.01） in North China. The results indicated the frost risk in the study region decreased over the past half century, and showed remarkable regional difference. These conclusions provide important information for agriculture and forestry managers in devising frost protection schemes.