The Arctic is warming twice as fast as the global average. This climate warming has the potential to cause dramatic shifts in the phenology of tundra plants, with implications for plant-pollinator interactions, surface albedo, and aboveground C stocks. However, we lack a clear picture of the degree to which tundra plant phenology is cued by temperature versus other drivers such as snowmelt date or day-length. Open top chambers (OTCs) provide a unique opportunity to experimentally disentangle the role of warming temperatures on tundra phenology. Here we use a recently updated dataset from the International Tundra Experiment (ITEX) covering 16 sites and 40 OTC warming experiments across arctic, subarctic, and alpine ecosystems with observations from 1992-2019 on each of six plant phenophases (green-up, flowering, end-of-flowering, fruiting, seed dispersal, and senescence). Our objectives were to determine (1) the magnitude and direction of plant phenology shifts under experimental warming; (2) whether certain species, functional groups, or geographic regions are most responsive; (3) whether effects of experimental warming are amplified by multiple years of warming (4) whether the magnitude and direction of responses are similar or different across phenophases and (5) whether the effects of experimental warming interact with inter-annual climate patterns.
Results/Conclusions
Overall plants in OTCs shifted all reproductive phenophases an average of two days earlier than plants growing in ambient conditions. Vegetative phases shifted less than reproductive phenophases, with slightly earlier green-up and later senescence in OTCs than ambient. Flowering and end-of-flowering shifted by similar magnitudes, resulting in no change in the duration of the flowering phenoperiod, while divergent responses in green-up and senescence suggest a slight extension of the growth period. Responses to OTC warming were relatively consistent across sites, plant species and functional groups. We also found no consistent influence of the duration of warming, site level soil moisture or latitude on plant responses. Taken together these results suggests that that (1) Climate warming will advance reproductive phenophases more than vegetative phenophases and have differing effects on the duration of phenoperiods. (2) Responses to experimental warming can be accurately assessed with short-term studies and OTCs retain their effectiveness over very long timeframes (20+ years). (3) Plant responses to OTC warming are largely consistent across species, functional groups, and geographic regions. Deciphering species and ecosystem level responses to warming is critical for a complete understanding of climate change impacts on rapidly changing tundra ecosystems.