Autumn Phenology and Its Covariation with Climate, Spring Phenology and Annual Peak Growth on the Mongolian Plateau

Using the normalized difference vegetation index (NDVI) and climate data, we calculated the end of the growing season (EOS; unit: day-of-year (DOY)) on the Mongolian Plateau and explored the effects of the climate, the start of the growing season (SOS), and the annual peak growth (APG, unit: NDVI) of vegetation and its timing (peak growth time, PGT) on the EOS for the period of 1982-2013. The spatial distribution pattern of the EOS on the plateau presented a gradual delay from south to north in Mongolia and from southwest to northeast in Inner Mongolia, and spatially it was highly related to vegetation producty. During 1982-2013, the area-averaged EOS varied between 265.2 and 278.3, and showed a slight but non-significant advancing trend of 0.6 days decade–1, with a breaking point occurring in 1993. This insignificant advance resulted from substantial spatial heterogeneities of the trend in EOS, with advances in widespread grassland-dominated regions and delays in southwestern Inner Mongolia. Preseason air temperature (preseason means of the periods prior to the EOS date related to the EOS variation) exerted positive effects on the EOS in wet and cold areas in northern Mongolia, while preseason precipitation exerted positive effects in widespread arid and semiarid regions in central grassland regions, with different preseason lengths varying according to meteorological variables and locations. More importantly, we identified strong influences of the SOS (r=0.46, p=0.008), APG (r=0.35, p=0.05), and PGT (r=0.76, p<0.001) on the EOS, which was almost universal for all biomes, suggesting first a strong carryover effect through seasonal cycles of plants on the EOS and second that meteorological variables alone may not fully explain the mechanism of EOS variations. We conclude that these carryover effects, which may be not well considered in current EOS studies, should be incorporated into the prediction model of EOS.