Phenology of Five Shrub Communities along an Elevation Gradient in the Qilian Mountains, China

Phenology indicates the response of ecosystem dynamics to climate change. Shrubs are an important component of alpine forests, and play a key role in forest ecosystem function, especially in semiarid alpine regions. In 2015, we observed the dynamics of phenology in five shrub communities along an elevation gradient (2600-3300 m) in the Qilian Mountains. Our results showed that the length of the growing season decreased from 153 days for Caragana tangutica to 150 days for Berberis diaphana, 149 days for Potentilla fruticosa L., 144 days for Caragana jubata (Pall.) Poir., and 134 days for Salix gilashanica C. Wang et P. Y. Fu. The accumulated temperature of the five shrub communities during the growing season varied from 1735.4 degrees C for C. tangutica to 1051.3 degrees C for C. jubata. The beginning of the growing season was earlier at lower, than at higher, elevations, while the end of the growing season was later at lower, than at higher, elevations. Elevation and aspect were two important environmental factors that affected shrub phenology. In our study, low temperature, coinciding with the occurrence of early frost, particularly in higher elevations, was the key factor in promoting end-of-season shrub growth cessation.