Abstract
Vegetation phenology is an important indicator of global climate change, and the response of grassland phenology to climate change is particularly sensitive in ecologically fragile areas. To enhance the ecological security of the Tibetan Plateau, it is crucial to determine the relationship between fluctuations in the start of the growing season (SOS) and the response to environmental factors. We investigated the trends of the intra-annual (ten-day) and interannual spatiotemporal dynamics of the SOS on the Northeast Qinghai-Tibet Plateau (NQTP) from 2000–2020 with MOD09GA data. We identified the response relationships with environmental factors (climate, terrain) using the maximum value composite method and the Savitzky–Golay filtering and dynamic threshold method. The SOS was concentrated from the 110th to 150th days; the average annual SOS was on the 128th day, with a spatial pattern of “early in the east and late in the west”. The overall trend of the SOS was advanced (45.48%); the regions with the advanced trend were mainly distributed in the eastern part of the NQTP. The regions with a delayed SOS were mainly concentrated in the higher-altitude regions in the southwest (38.31%). The temperature, precipitation and SOS exhibited a reverse fluctuation trend around the midpoint of 2010. Precipitation affected the SOS earlier than temperature. When temperature became a limitation of the SOS, precipitation had a more significant regulatory effect on the SOS. The SOS and aspect, slope and altitude were distributed in axisymmetric, pyramidal and inverted pyramidal shapes, respectively. The SOS on shaded slopes was earlier and more intensive than that on sunny slopes. With increasing slope, the area of the SOS decreased, and it occurred later. The SOS area was largest at 4500–5000 m and decreased at lower and higher altitude intervals. The SOS occurred later as altitude increased.
Highlights
Li et al [15] used a phenology camera to study the vegetation phenology of four alpine grasslands with different grazing intensities from 2015 to 2017, and the results revealed differences in the start of the growing season (SOS) of alpine grasslands with different grazing levels
Qinghai Province is an important part of the Qinghai-Tibet Plateau (QTP), with a total area of 69.66 × 104 km2, making it the fourth-largest province in China, and it is located in the interior of Northwest
The positive correlation between the precipitation and SOS in late April was as high as 77.09%, which indicates that precipitation plays a positive role in the SOS in late
Summary
Human activities are the main catalyst for current global warming [1]. The massive emissions of greenhouse gases since the industrial revolution have led to varying degrees of land surface and ocean surface warming, with the rate of warming in the last 20 decades being twice that of the 20th century [2]. Vegetation ecosystems play an extremely important role as a bridge for material and energy exchange between the land and the atmosphere [3]; they are significantly changing due to the warming climate [4]. It has been shown that climate warming advances spring phenology in forests and grasslands in cold-temperate regions [5]. Vegetation phenology refers to the cyclical growth of vegetation
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