Geographic variation in adaptation and population movement guidelines in restoration species in the western United States
Populations are often adapted to local environments. Restoration efforts on public lands in the Western US have had mixed success for a number of reasons including the extreme climatic conditions. To yield successful outcomes in restoration efforts the use of native plant material from areas similar to the restoration site is essential. Thus, seed transfer zones have been developed to guide restoration efforts. A provisional seed zone map has been developed for species without species-specific seeds zones. This provisional map integrates climatic variables along with level III ecoregions and has been found to account for the majority of variation among populations of grass and forb species. For a handful of species, seed zone maps specific to the species have been developed, but have yet to be tested. Here we present a summary of seed transfer guidelines for restoration in the western United States. Then focus on our current investigation of the efficacy of seed zones for bluebunch wheatgrass (Pseudoroegneria spicata) to ensure successful establishment and allow for long-term adaptation by maintaining genetic diversity. We test the hypothesis that in the long-term populations from local seed zones will better establish, survive, and reproduce. To test this hypothesis, we established a reciprocal transplant study in two broad regions each with eight seed zones with each seed zone represented by four to five wild populations.
To increase the success of restoration, we suggest that land managers use provisional or species specific seed zones in conjunction with species-specific information and knowledge of microsite differences to guideline seed transfers/population movements. Results from previous works and this study support this suggestion and will improve success rates of restoration in the Western United States. Focusing on one species we examined the effectiveness of seed zones by comparing differences in establishment, survival, and reproduction of bluebunch wheatgrass from local seed zones compared to non-local seed zones planted in 16 common gardens. In the first year of this study, we found that overwinter survival was high among all source populations planted in different seed zones. This likely is due to above average temperatures and precipitation among sites. By substituting space for time to evaluate different populations in different climates, this study explores the consequences of changing climates for adaptation. Population movement guidelines and associated seed zones can be adjusted based on results from this study and management objectives.