Increased growth of Qinghai spruce in northwestern China during the recent warming hiatus

The effect of warming-induced drought stress on tree growth has been frequently discussed, and a decline in the growth of forest and increased mortality has been reported for many areas of the world. A hiatus in the global warming trend began around the year 2000, but how tree growth has responded to this warming slowdown remains unclear. Here we present a study of the recent impacts of climate change on Qinghai spruce (Picea crassifolia) growth using 38 tree-ring records collected from the Qilian Mountains in northwestern China. Results indicate that there was a clear increase in Qinghai spruce growth during the recent warming hiatus. Similarly, regional vegetation growth also improved as indicated by NDVI variations, which is closely associated with regional climate changes. The mean air temperature increased dramatically during the period 1980-2001, whereas precipitation decreased slightly. This combination of warmer temperatures and reduced precipitation created drought conditions that limited the growth of Qinghai spruce during this period. Since 2001, the warming trend has slowed, whereas precipitation has clearly increased, creating moist conditions as reflected by the higher drought index (SPEI). A decline in drought pressure, coupled with an increasingly long growing season, might be the main reason for the recent improvement in the growth of Qinghai spruce in the Qilian Mountains. Our results suggest that the growth of Qinghai spruce is very sensitive to climate change. A better understanding of future climate changes and their likely impact on tree growth should be of significant interest to forest managers.