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Abstract

The ability for communities to preserve their structure and function in the face of climate change is partially dependent on whether or not species within them can successfully reproduce. Two important measures of reproduction in many plant communities are the timing of flowering (“flowering phenology”) and the number of flowers that individuals within the community can produce. In addition to broad-scale climate, variation in climatic factors – such as temperature and soil moisture - across the scale of meters (“microclimates”) have the ability to impact both flowering phenology and flower production. In the alpine, the upward movement of shrubs, also known as shrub encroachment, changes local microclimates through shading and catching wind-blown snow. This study focuses on the effects that shrub-induced microclimates are having on 21 different alpine angiosperm species within a plant community. To test this, we measured the number of flowers that each species produced, as well as their flowering phenology. We established 54 shrub plots at Niwot Ridge, Colorado, each paired with a plot that was not influenced by any shrubs (“open” plots). Our plots varied in aspect, with half of them north-facing and half of them south-facing, to control for temperature variation. We found that shrubs delayed peak community flowering by about one week, as well as producing a  statistically detectible decrease in the average number of flowers produced at the community level. Our results suggest that a) upward movement of shrubs into the tundra is changing the flowering phenology of alpine communities, as well as decreasing the number of flowers individuals in the community produce and b) a factor other than temperature is likely driving these shrub-induced changes in alpine community flowering phenology. The gradual shift in flowering phenology due to climate change has the potential to impact community structure, as well as implement cascading effects for other species. Key words: flowering phenology, alpine, shrub encroachment, microclimates