The subalpine perennial herb Delphinium nuttallianum Pritzel (formerly D. nelsonii Greene) (Ranunculaceae) provides a model system for studying the impact of climate conditions on plant reproductive biology and fitness. First, as a key food source for hummingbirds and bumblebees, this species is an important member of the subalpine flora. Second, as one of the first spring wild flowers in subalpine meadows, D. nuttallianum is likely to be particularly sensitive to seasonal shifts induced by anthropogenic climate changes. Finally, an abundance of published data describes the factors that limit reproduction in this species, the nature of pollinators attracted to it, and the impact of this species on other members of the subalpine plant community.

The goal of this project was to isolate climate variables that impact flowering phenology and fitness in D. nuttallianum. The measured variables reflect climate components that are predicted to change as a result of human-induced (anthropogenic) global climate change.

Chapter 1 reviews climatic conditions in high altitude and latitude habitats, along with studies describing the impact of climate on plants in these environments. The focus is on current climate conditions as well as on predicted changes in climate for these habitats resulting from anthropogenic climate change. Chapter 2 describes an experiment conducted to determine the effects of a single climate variable, snowmelt date, on the timing of flowering in D. nuttallianum. Previous studies have shown a correlation between snowmelt date and flowering, but were not designed to remove potentially confounding variables. Removing snow from meadows containing D. nuttallianum in the Colorado Rocky Mountains induced population-wide shifts in the initiation of flowering time, and in the date of peak flowering, but not in the date plants finished flowering.Chapter 3 connects D. nuttallianum flowering phenology with aspects of plant fitness. By following the D. nuttallianum plants used for the snow-removal experiment described in Chapter 2 and their progeny I was able to assess the impact of flowering time on several components of plant fitness. Of these components, flower number and total seed set were unchanged by snowcover manipulation, while seed weight and seedling size were positively affected by snow removal. These results suggest that earlier snowmelt, and a resulting longer growing season, might increase reproductive success in D. nuttallianum, at least in the short term.Chapter 4 presents natural observations of flowering time, seed production and quality, and gene flow in D. nuttallianum. Observations of natural variation in flowering time exceeded the experimental variation induced by both the meadow-warming (Chapter 5) and snow-removal experiments (Chapter 2). Plants that flowered earlier in the season tended to produce more, heavier, seeds. There were no significant differences in outcrossing rate for plants flowering at different points during the season.
In chapter 5, I present a study of flowering plant density and flower production for a population of D. nuttallianum in a warming experiment. Both flowering plant density and average number of flowers per plant were significantly lower in experimentally heated plots. There was also a year by treatment effect on bud abortion by plants.