Impact of climatic factors on vegetation dynamics in the upper Yangtze River basin in China

Abstract

It is necessary to understand vegetation dynamics and their climatic controls for sustainable ecosystem management. This study examines the vegetation dynamics and the effect of climate change on vegetation growth in the pristine conditions of 58 woodland National Nature Reserves (NNRs) located in the upper Yangtze River basin (UYRB) in China which are little influenced by human activities. Changes in the normalized difference vegetation index (NDVI), precipitation, and temperature in the selected NNRs were observed and analyzed for the period between 1999 and 2015. The relationship between time-lag effect of climate and changes in the NDVI were assessed using Pearson correlations. The results showed three major trends. 1) The NDVI increased during the study period; this indicates an increase in the amount of green vegetation, especially due to the warmer climate during the growing season. The NDVIs in March and September were significantly affected by the temperature of the previous months. Spring temperatures increased significantly (P < 0.05) and there was a delay between climatic factors and their effect on vegetation, which depended on the previous season. In particular, the spring temperature had a delayed effect on the NDVI in summer. 2) The way in which vegetation responds to climatic factors varied significantly across the seasons. Temperature had a greater effect on the NDVI in spring and summer and the effect was greater at higher altitudes. A similar trend was observed for precipitation, except for altitudes of 1000–2000 m. 3) Temperature had a greater effect on the NDVI in spring and autumn at higher altitudes. The same trend was observed for precipitation in summer. These findings suggest that the vegetation found in NNRs in the upper reaches of the Yangtze River was in good condition between 1999 and 2015 and that the growth and development of vegetation in the region has not been adversely affected by climate change. This demonstrates the effectiveness of nature reserves in protecting regional ecology and minimizing anthropogenic effects.