Shifts in spring phenophases, frost events and frost risk for woody plants in temperate China

In light of recent warming trends around the world, a growing concern is that the timing of spring phenophases in plants will occur earlier and that plants will therefore suffer from spring last-frost events more often. The changes in frost risks could have significant implications for agricultural and forestry systems. In this study, we investigated whether plant phenophases changed at a higher or lower rate compared to potentially damaging spring frost events in the temperate monsoon area of China. Based on phenological data derived from the Chinese phenological observation network and meteorological data from 15 study sites, changes in first-leaf dates and first-flowering dates for 12 deciduous woody plants were analyzed in comparison to last-frost dates. The results show that plant phenophases in spring advanced by a mean trend of -0.17 d yr(-1) from 1963 to 2011. Over the same period, last-frost dates advanced at a rate of -0.23 d yr(-1) (-0.51 to 0.10 d yr(-1)). Because the spring frost risk is decided by the relationship between last-frost date and plant phenophases in spring, the frost index, defined as the difference in days between the onset of spring phenophases and the last-frost date, was used to assess the frost risk. The significantly increased frost index (0.087 d yr(-1), p < 0.01) suggests that the frost risk of plant phenophases in the study area declined over the nearly half-century study period. These findings provide the basis for tackling frost risk in the region.