The timing of life history events, or phenology, has important consequences for organismal fitness. In plant communities, flowering time can impact plant seed set due to seasonal variations in the biotic and abiotic environment experienced by individuals. Temporally variable abiotic factors that impact seed set include the threat of frost or available soil moisture, and biotic factors include the phenology of pollinators and the availability of conspecific pollen donors. Whilst studies have shown that flowering time impacts seed set of many plant species, the relative fitness of species in communities is rarely examined yet likely impacts long-term plant coexistence and diversity. We conducted a large-scale field experiment on subalpine wildflower communities, advancing flowering time of plants by accelerating snowmelt, a phenological trigger for many species in this system. We worked in seven spatially independent sites, each with a paired snowmelt acceleration and control plot. In manipulation plots, we successfully advanced species flowering time by up to three weeks, a substantial period in the brief subalpine growing season. Our manipulations did not have a detectable effect on pollinator communities, thus potentially creating temporal mismatches between plant and pollinator communities. We collected and counted seeds from 12 plant species, and accounting for possible drivers of changes in seed set, including pollen limitation, floral neighborhood and soil moisture.
Results/Conclusions
Experimentally accelerated flowering increased or decreased seed set in some species, there was no detectable impact on the relative fitness of species within communities. In particular, there was no detectable change in the relative proportion of seeds produced from species that are pollinator-dependent relative to selfing species. While preliminary, our results suggests that communities may be somewhat buffered from the impacts of early snowmelt and phenological change. Alternatively, impacts may be slow to accumulate, and if so will require long-term data to elucidate. Our study is one of the first to examine community-level responses to experimental phenological shifts.