Vegetation cover variation in the Qilian Mountains and its response to climate change in 2000–2011

Abstract

An understanding of variations in vegetation cover in response to climate change is critical for predicting and managing future terrestrial ecosystem dynamics. Because scientists anticipate that mountain ecosystems will be more sensitive to future climate change compared to others, our objectives were to investigate the impacts of climate change on variation in vegetation cover in the Qilian Mountains (QLM), China, between 2000 and 2011. To accomplish this, we used linear regression techniques on 250-m MODIS Normalized Difference Vegetation Index (NDVI) datasets and meteorological records to determine spatiotemporal variability in vegetation cover and climatic factors (i.e. temperature and precipitation). Our results showed that temperatures and precipitation have increased in this region during our study period. In addition, we found that growing season mean NDVI was mainly distributed in the vertical zone from 2,700 m to 3,600 m in elevation. In the study region, we observed significant positive and negative trends in vegetation cover in 26.71% and 2.27% of the vegetated areas. Correlation analyses indicated that rising precipitation from May to August was responsible for increased vegetation cover in areas with positive trends in growing season mean NDVI. However, there was no similar significant correlation between growing season mean NDVI and precipitation in regions where vegetation cover declined throughout our study period. Using spatial statistics, we found that vegetation cover frequently declined in areas within the 2,500–3,100 m vertical zone, where it has steep slope, and is on the sunny side of mountains. Here, the positive influences of increasing precipitation could not offset the drier conditions that occurred through warming trends. In contrast, in higher elevation zones (3,900–4,500 m) on the shaded side of the mountains, rising temperatures and increasing precipitation improved conditions for vegetation growth. Increased precipitation also facilitated vegetation growth in areas experiencing warming trends at lower elevations (2,000–2,400 m) and on lower slopes where water was more easily conserved. We suggest that spatial differences in variation in vegetation as the result of climate change depend on local moisture and thermal conditions, which are mainly controlled by topography (e.g. elevation, aspect, and slope), and other factors, such as local hydrology.