Search

• High spatial resolution data has a higher accuracy in acquiring SOS. • The SOS changes are mainly affected by spring temperature and winter precipitation. • At lower elevations, advancing SOS increased spring and summer growth. • At higher elevations, delayed SOS leads to decreased spring growth and increased summer growth. • The effect of SOS on vegetation growth weakens from the spring to summer seasons. Vegetation spring phenology in mountains has undergone profound changes due to climate change. In this paper, which made use of the Harmonic Analysis of Time Series (HANTS) smoothing algorithm and logistic models, the start of the vegetation growing season (SOS) inferred from MODIS datasets with different spatial resolutions from 2001 to 2018 was extracted. The MODIS data closest to the ground-truth observation data were then selected to reflect spring phenology. Combined with temperature and precipitation data, the spatio-temporal patterns and elevation-dependent change mechanisms of the SOS and its legacy effect on vegetation growth in the mountains of northwest Mongolia was examined and the following results were obtained: (1) Compared with the MOD13A1 and MOD13A2 datasets, the high spatial resolution MOD13Q1 dataset provided stronger correlations and the lowest errors with ground-truth observation data. (2) In this study, the SOS usually occurred between 120 and 152 day-of-year (DOY) with the earlier SOS detected in the low-elevation areas. Later SOS occurred mostly in the higher elevation areas. (3) The spatio-temporal variations in the SOS are mainly influenced by both spring temperature and winter precipitation, with increasing precipitation in winter tending to delay the SOS, while increasing spring temperature tended to advance the SOS. (4) At elevation gradient, the spring temperature showed a significant negative effect on SOS at all elevations, except between 1037 m and 1137 m and 3337 m to 3437 m above sea level (ASL), with a significant positive correlation between SOS and winter precipitation between 1337 m and 2937 m ASL. It is expected that spring temperature is closely linked to the heat accumulation of plants, while winter precipitation indirectly affects the temperature in spring. (5) In lower elevation areas (below 1437 m ASL), the SOS was found to be negatively correlated with spring and summer growth, with advancing SOS leading to increased vegetation growth during spring and summer. In higher elevation areas (above 1437 m ASL), the SOS was significantly negatively correlated with spring growth and positively correlated with summer growth. Hence, delayed SOS leads to decreased spring growth and increased summer growth. Also, we found the effect of SOS on vegetation growth gradually weakened from spring to summer. These findings can help to determine the mechanisms and functional consequences of spring phenological changes in mountain regions. [ABSTRACT FROM AUTHOR]

• In the Mongolian Plateau, wildfires occurred frequently from 2001 to 2015. • Advancing spring phenology more obvious in the Inner Mongolian than in Mongolia. • Preseason temperature has the greatest impact on the spring phenology. • In a typical fire area, the SOS in the fire zone shifted to earlier in the year. The variation of land surface phenology (LSP) in natural ecosystems has received much attention at the regional and global scales. In this paper, we explore the relationship between variations in the start of the growing season (SOS) and their direct and indirect drivers for the Mongolian Plateau. Our results show that wildfire events mainly occurred in 2001, 2002, 2006, 2008, 2011, and 2016. The frequency of Mongolian wildfires is lower in the south and west, but higher in the east and north. The frequency of wildfires in Inner Mongolia (China) shows a spatial gradient, with a higher frequency in the northeast and a lower frequency in the southwest. Late SOS was most widely distributed in the southeast of Mongolia and the south of Inner Mongolia. The vegetation in the grassland or forest areas showed a comparatively early SOS, between the 110th and 130th day-of-year (DOY). The advancing trends of the SOS were mainly distributed around the northeast Mongolian Plateau, which is more obvious in Inner Mongolia (China) than in Mongolia. Under the control of precipitation (pre) and solar radiation, the preseason average temperature (T mean) in most areas of the study area is from 0 to 3 months. In the Mongolian Plateau, negative partial correlations between the SOS and preseason T mean was mainly concentrated in the northern and northeastern parts of the study area, while positive correlations were mainly distributed in the central and southeastern parts. We also found that in addition to climate factors, wildfires have an impact on the SOS. After wildfires, the enhanced vegetation index (EVI), T mean and SOS showed a significant difference in the greening period between the reference region and the burned area. Compared with the reference zone, the SOS in the fire zone shifted to being earlier. This study, therefore, provides a scientific basis and reference for understanding variations in the SOS in the study area and the response of the SOS to climate change and wildfires. [ABSTRACT FROM AUTHOR]