The spatiotemporal characteristics of spring phenophase changes of Fraxinus chinensis in China from 1952 to 2007

We selected widely distributed and well observed plant species Fraxinus chinensis to study the formation mechanism of geographical distribution of the plant phenophase changes and revealed their spatiotemporal dynamics in China. Based on the first leaf date (FLD) data at 12 sites derived from Chinese Phenological Observation Network (CPON) and related meteorological data, we developed and validated the process-based model of FLD for Fraxinus chinensis. After reconstructing data series of FLD for Fraxinus chinensis over the study area from 1952 to 2007, we analyzed different spatiotemporal patterns of phenophase changes of this species. The results suggested that the process-based model was able to simulate the FLD accurately for Fraxinus chinensis on large spatial and temporal scales, because of the consideration of different budding rate responded to the air temperatures during the dormancy and the quiescence in accordance with the physiological mechanism of plants. The geographical distribution of the spring phenology in temperate regions was determined by the spatial pattern of daily average air temperature. The changes of FLD for Fraxinus chinensis revealed significant phenological advances in most areas. However, it showed delayed trends in a few sites. The overall average change trend was −1.1 days/decade. This result was consistent with the advanced trend in other regions of the North Hemisphere. The changes of FLD showed a noticeable regional variation with clearer advance in the north than in the south. The FLD in northern China showed an average advance as high as −2.0 days/decade (P<0.01). And the advance in northeastern and northwestern China was respectively −1.5 and −1.4 days/decade (P<0.01). Furthermore, eastern and central regions showed a minor trend, which was −1.0 days/decade (P<0.05). The smallest and non-significant advance appeared in southwestern and southern China.