Assessing temperature sensitivity of subalpine shrub phenology in semi-arid mountain regions of China

Abstract

Subalpine shrubs are undergoing, or have experienced profound changes by force of recent climate anomalies, such as the alteration in temporal niche of phenophases and the dynamic interaction with ambient conditions. As cold biomes in high-altitude ecoregions, they have drawn a growing concern of the potential vulnerability to current and future climate change. In this study, we retrieved the time series (2000–2013) of satellite-based phenological transitions (the onset and offset of vegetative growth) for subalpine shrubs at five individual sites in the Qilian Mountains in northwestern China. Our goals were to identify the climatic constraints on the timing of leaf-out and leaf-fall, and to project these phenological patterns under the future climate conditions. To achieve these goals, the relationships between these regional phenological events and climate variables were investigated with univariate and multivariate time series models, and the future phenological dynamics were forecasted for two decades based on the best predictive models under the A2 and B2 of IPCCs Special Report on Emissions Scenarios (SRES). Our results generally revealed site-dependent phenology–climate relationships, which involved an immediate phenological response to the mean or minimum temperature in the corresponding month of occurrence, and a lagged cumulative climate effect across preceding months and seasons. Average temperature during a certain period has been demonstrated as an important limiting factor for plant growth. However, our results also provided evidence for the minimum temperature controls of the development of phenological events in subalpine shrublands, possibly due to a close association with the frequency of frost risk in spring and autumn. Under future climate conditions, an overall lengthening of the active growing season is expected at each of the study sites depending on elevation. Consequently, net carbon uptake by shrubs will benefit from the increased temperature.