Global climate change has caused shifts in the phenology of plants. Over time, small changes in the timing of flowering and reproduction of plants may have large impacts on community composition and biodiversity. Here we ask how recent increases in winter precipitation, summer air temperature, and nitrogen (N) deposition alter plant phenology in moist meadow alpine tundra of the Rocky Mountains. In 1m² plots, we manipulated summer temperatures using open-topped chambers, snowpack using small snowfences, and N availability using fertilizer, alone and in all possible combinations. Every 2-3 days throughout the growing season, we recorded first flowering date and flower presence for all species. For the most common species, we also recorded flower number at peak flowering date and estimated seed production.

Results/Conclusions

We found that response to treatments differed among species. Grasses, but not forbs, flowered earlier in response to N addition. Many species flowered earlier when N and snowpack were increased simultaneously. Geum rossii, the most common forb in the moist meadow tundra flowered earlier with increased temperatures. Another common forb, Bistorta bistortoides, increased flower production with temperature. Our results suggest that alpine phenology is likely to be altered by environmental changes, particularly by warmer temperatures and N deposition. Future changes in the plant composition of the tundra will depend on the relative strength and interaction of global change factors.