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 °C for C. tangutica to 1051.3 °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.

Analyzing the physiological response of trees to climate change in the Qilian Mountains region is key to studying the impact of global change on forest ecosystems in the semiarid alpine region of Northwest China. The leaf area index (LAI) of the canopy of a forest is an important input parameter for simulating carbon and water cycles in forest ecosystems. Studying the relationship between LAI and environmental factors can provide a scientific basis for accurately describing the structure, function, and ecohydrological processes of forest ecosystems and theoretically guide for sustainable management of water conservation in forests. Methods: In this study, the LAI of the Picea crassifolia canopy was monitored for 2 years (2015–2016) by field observations, and its dynamic changes were analyzed. The relations between LAI and air temperature (AT), precipitation (P), soil temperature (ST), and soil water content (SWC) were studied using Pearson's correlation and multiple regression analyses. The results were as follows: seasonal variations in LAI showed a single-peak curve, which first increased, reached a maximum, remained relatively stable, and then decreased. The maximum value was 4.02 and 4.18 relatively observed in mid-August 2015 and 2016. The LAI of the P. crassifolia canopy in different months was positively correlated with AT and P. It was correlated between the LAI of the canopy with ST₄₀₋₆₀ in May and June (p < 0.05) and was also highly positively correlated between the LAI of the canopy with ST₆₀₋₈₀, ST_mean, and SWC₆₀₋₈₀ in July and August (p < 0.01). There was a positive correlation between the LAI of the canopy with SWC₀₋₆₀ and SWC_mean in July and SWC₀₋₆₀ and SWC_mean in August (p < 0.05). The LAI of the canopy was affected by AT and ST in May and July, AT and P in June, P in August, and P and ST in September. Our study implied that the rapid increase period of the LAI of the canopy was from late May to early July. The LAI of the canopy was more influenced by temperature and water in July and August. In addition, the LAI of the canopy has significant seasonal variation although it is evergreen coniferous tree species.