Spring phenology of a dryland steppe plant community: potential implications of functional type dynamics for wildlife migration

Context Plant communities will experience compositional shifts as a result of climate change. Shifting functional type prominence, through changes in suitability of cool-season C 3 and warm-season C 4 grasses, could alter plant community phenology, which could prove impactful in ecosystems where plant communities provide valuable forage to local migratory species. Objectives We investigated: (1) the differences in phenology and early-season biomass contribution of key functional types and (2) the extent to which mule deer migration pathways could experience altered forage availability through plant community changes. Methods We tracked growth and biomass of C 3 and C 4 grass individuals in western Wyoming through the growing season to quantify the phenology and productivity of both functional types. We also compared results of a plant community model to regional mule deer migration pathways. Results C 4 grasses reached peak biomass 48–60 days later than other functional types. Small C 3 grasses and forbs had similar phenological progression, followed by large C 3 grasses and then C 4 grasses. Large C 3 grass individuals contributed most to productivity and growth rate peaked 22 days after small C 3 grasses. With climate change, all functional types are projected to increase across 60–70% of deer migration pathways by 3–5 g/m2. Conclusions Our study indicates that mule deer migration most closely coincides with the phenology of small C 3 grasses and forbs, and there is up to a 2-month difference in the regional green-up between functional types. Climate change will have variable impacts on species and the timing of resource availability. These results provide valuable regionally specific information on early-season growth.