UC Davis

Changes in phenology, or the recurring timing of life history events, are one of the most apparent ecological effects of climatic warming. In general, plants have begun to emerge earlier as temperatures have warmed. Warming, however, may not be solely responsible for phenological advance observed in plants—biotic factors such as herbivory may also be involved. This study aimed to understand the effect that the presence and timing of herbivory have on plant phenology. Using 9 years of data from an herbivore exclosure experiment near Kangerlussuaq, Greenland, we investigated whether the timing of plant emergence and flowering, as well as the length of time between those two life stages, differed between plants that were exclosed from or exposed to large herbivores, caribou (Rangifer tarandus) and muskoxen (Ovibos moschatus). Our results indicate that plants exposed to herbivory emerged nearly one day earlier and flowered nearly 1.5 days earlier than plants exclosed from herbivory. Additionally, the length of time between emergence and flowering was nearly one day longer for plants inside of herbivore exclosures. We also analyzed whether plant emergence and flowering phenology, as well as the duration of the emergence phase before flowering, were related to the annual timing of herbivore presence at the study site. Results suggested that emergence and flowering occurred earlier in years when caribou and muskox occurred earlier at the study site. Earlier herbivore presence was also associated with a longer duration between emergence and flowering, though this effect was weaker on plots exposed to herbivory suggesting that herbivory may constrain a lengthening of emergence. Our findings lend support to the notion of phenological escape which suggests that plants avoid or minimize tissue loss and its detrimental fitness consequences by accelerating phenophase progression under exposure to herbivory. This study highlights the importance of better understanding the role of biotic interactions in phenological responses to climate change.