Effects of permafrost degradation on alpine grassland in a semi-arid basin on the Qinghai–Tibetan Plateau

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.

[1]  E. Small,et al.  The impact of soil reflectance on the quantification of the green vegetation fraction from NDVI , 2005 .

[2]  Yong Zha,et al.  Assessment of grassland degradation near Lake Qinghai, West China, using Landsat TM and in situ reflectance spectra data , 2004 .

[3]  G. Cheng,et al.  Responses of permafrost to climate change and their environmental significance, Qinghai‐Tibet Plateau , 2007 .

[4]  Bunkei Matsushita,et al.  A New Method to Define the VI-Ts Diagram Using Subpixel Vegetation and Soil Information: A Case Study over a Semiarid Agricultural Region in the North China Plain , 2008, Sensors.

[5]  Bo-Hui Tang,et al.  An application of the Ts–VI triangle method with enhanced edges determination for evapotranspiration estimation from MODIS data in arid and semi-arid regions: Implementation and validation , 2010 .

[6]  Guodong Cheng,et al.  Changes in frozen ground in the Source Area of the Yellow River on the Qinghai–Tibet Plateau, China, and their eco-environmental impacts , 2009 .

[7]  Short communication A spectral reflectance-based approach to quantification of grassland cover from Landsat TM imagery , 2003 .

[8]  Donglian Sun,et al.  Note on the NDVI‐LST relationship and the use of temperature‐related drought indices over North America , 2007 .

[9]  Qingbai Wu,et al.  Changes in active layer thickness over the Qinghai‐Tibetan Plateau from 1995 to 2007 , 2010 .

[10]  K. Weber,et al.  Multi-sensor Analyses of Vegetation Indices in a Semi-arid Environment , 2010 .

[11]  T. Carlson.  An Overview of the “Triangle Method” for Estimating Surface Evapotranspiration and Soil Moisture from Satellite Imagery , 2007, Sensors (Basel, Switzerland).

[12]  Chen Yunhao,et al.  Detecting Vegetation Fractional Coverage of Typical Steppe in Northern China Based on Multi-scale Remotely Sensed Data , 2003 .

[13]  Martha C. Anderson,et al.  Use of NDVI and Land Surface Temperature for Drought Assessment: Merits and Limitations , 2010 .

[14]  Multisensor Comparisons for Validation of MODIS Vegetation Indices , 2006 .

[15]  Dominik Bänninger,et al.  stimating vegetation parameter for soil erosion assessment in an alpine atchment by means of QuickBird imagery , 2010 .

[16]  Wang Yibo,et al.  Effects of permafrost thawing on vegetation and soil carbon pool losses on the Qinghai–Tibet Plateau, China , 2008 .

[17]  Detecting Vegetation Fractional Coverage of Typical Steppe in Northern China Based on Multi-scale Remotely Sensed Data , 2003 .

[18]  Meixue Yang,et al.  Permafrost degradation and its environmental effects on the Tibetan Plateau: A review of recent research , 2010 .

[19]  Hua Yang,et al.  Improvement, Comparison, and Application of Field Measurement Methods for Grassland Vegetation Fractional Coverage , 2005 .

[20]  Jay Gao,et al.  A spectral reflectance-based approach to quantification of grassland cover from Landsat TM imagery , 2003 .