The decreasing spring frost risks during the flowering period for woody plants in temperate area of eastern China over past 50 years.

The temperate monsoon area of China is an important agricultural region but late spring frosts have frequently caused significant 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 an average rate of −1.52 days/decade in Northeast China ( P<0.01) and −2.22 days/decade ( P<0.01) in North China. Over the same period, the number of frost days in spring decreased and the last frost days 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, exhibited a decreasing trend of −0.37% per decade (insignificant) in Northeast China and −1.80% per decade ( P<0.01) in North China, implying that frost risk has reduced over the past half century. These conclusions provide important information to agriculture and forest managers in devising frost protection schemes in the region. [ABSTRACT FROM AUTHOR]