Divergent shifts and responses of plant autumn phenology to climate change on the Qinghai-Tibetan Plateau

Abstract

Autumn phenology along with spring/summer phenology controls the length of the vegetation growing season and significantly influences ecosystem biogeochemical cycles. Many previous studies have focused on spring/summer phenology. However, fewer studies have addressed autumn phenology because of no available or insufficient observations. Based on a series of long-term and continuous observations of autumn phenological events (8000+ records) on the Qinghai-Tibetan Plateau (QTP), we made a comprehensive assessment of autumn phenological shifts and their responses to climate change during the period from 1981 to 2011. Although a significantly delayed overall trend in autumn phenology was observed across the QTP from 1981 to 2011, the autumn phenologies showed divergent shifting trends and responses to climate change among plant species, phenological events, study periods and thermal conditions. Larger variations were observed for the occurrence dates of fruit-related events than foliar events. Significantly advanced shifts in autumn phenology were observed for woody plants (mostly owing to fruit-related phenological events), while significantly delayed shifts were observed for herbaceous plants (mostly owing to foliar events). The autumn phenology of woody plants varied little among plant species, recording periods and thermal conditions but varied greatly under different temperature change trends. The autumn phenology of herbaceous plants varied greatly among plant species, recording periods, thermal conditions and sites with different temperature change trends. The occurrence dates of most phenological events for herbaceous plants were positively correlated with the preseason temperature and negatively correlated with the preseason precipitation, while opposite relationships were observed for woody plants. Our results provide new field evidence for the dispersive changes in autumn phenology on the QTP and suggest that the dispersive shifts in autumn phenology and their different responses to climate warming should be considered when assessing the impacts of climate change on vegetation dynamics and ecosystem biogeochemical cycles.