摘要：Permafrost on the Qinghai–Tibetan Plateau (QTP) has degraded over the last few decades.
Its ecological effects have attracted great concern. Previous studies focused mostly at plot
scale, and hypothesized that degradation of permafrost would cause lowering of the water
table and drying of shallow soil and then degradation of alpine grassland. However, none
has been done to test the hypothesis at basin scale. In this study, for the first time, we
investigated the relationships between land surface temperature (LST) and fractional
vegetation cover (FVC) in different types of permafrost zone to infer the limiting condition
(water or energy) of grassland growth on the source region of Shule River Basin,
which is located in the north-eastern edge of the QTP. LST was obtained from
MODIS Aqua products at 1 km resolution, while FVC was upscaled from quadrat
(50 cm) to the same resolution as LST, using 30 m resolution NDVI data of the
Chinese HJ satellite. FVC at quadrat scale was estimated by analyzing pictures
taken with a multi-spectral camera. Results showed that (1) retrieval of FVC at
quadrat scale using a multi-spectral camera was both more accurate and more
efficient than conventional methods and (2) the limiting factor of vegetation growth
transitioned from energy in the extreme stable permafrost zone to water in the
seasonal frost zone. Our study suggested that alpine grassland would respond
differently to permafrost degradation in different types of permafrost zone. Future
studies should consider overall effects of permafrost degradation, and avoid the
shortcomings of existing studies, which focus too much on the adverse effects.
