Abstract
The grassland ecosystem in the Northern-Tibet Plateau (NTP) of China is verysensitive to weather and climate conditions of the region. In this study, we investigate thespatial and temporal variations of the grassland ecosystem in the NTP using theNOAA/AVHRR ten-day maximum NDVI composite data of 1981-2001. The relationshipsamong Vegetation Peak-Normalized Difference Vegetation Index (VP-NDVI) and climatevariables were quantified for six counties within the NTP. The notable and unevenalterations of the grassland in response to variation of climate and human impact in theNTP were revealed. Over the last two decades of the 20th century, the maximum greennessof the grassland has exhibited high increase, slight increase, no-change, slight decrease andhigh decrease, each occupies 0.27%, 8.71%, 77.27%, 13.06% and 0.69% of the total area ofthe NTP, respectively. A remarkable increase (decrease) in VP-NDVI occurred in thecentral-eastern (eastern) NTP whereas little change was observed in the western andnorthwestern NTP. A strong negative relationship between VP-NDVI and ET0 was foundin sub-frigid, semi-arid and frigid- arid regions of the NTP (i.e., Nakchu, Shantsa, Palgonand Amdo counties), suggesting that the ET0 is one limiting factor affecting grasslanddegradation. In the temperate-humid, sub-frigid and sub-humid regions of the NTP (Chaliand Sokshan counties), a significant inverse correlation between VP-NDVI and populationindicates that human activities have adversely affected the grassland condition as waspreviously reported in the literature. Results from this research suggest that the alterationand degradation of the grassland in the lower altitude of the NTP over the last two decades of the 20th century are likely caused by variations of climate and anthropogenic activities.
Highlights
The Northern-Tibet Plateau (NTP) covers a vast territory of the western China with an average altitude of 4,500 m
Monitoring and quantifying dynamics and spatial variability of the grassland ecosystems of the world is crucial for understanding and mitigating the grassland degradation caused by natural and anthropogenic forces
A moderate to high increase of Vegetation Peak-Normalized Difference Vegetation Index (VP-Normalized Difference Vegetation Index (NDVI)) from 1981 to 2001 has occurred in the east part of the NTP, which is located at the low altitude zone (Nakchu, Shantsa, and Palgon counties)
Summary
The Northern-Tibet Plateau (NTP) covers a vast territory of the western China with an average altitude of 4,500 m. It is generally believed that the occurrence and expansion of grassland degradation due to acidification and desertification over the NTP are closely related to changes in climate, ecological condition and human activity, such as overgrazing, excessively timber cutting and digging [2,3,11]. Under the dual influences of natural and human factors, a large expanse of grassland in the NTP region has seriously degraded [2, 10]. We investigate the spatial and temporal variations and possible causes of the grassland ecosystem in the NTP using a 19-year time series of the Normalized Difference Vegetation Index (NDVI) data and corresponding climate and demographic data
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