Plant species span a range of climates from arid desert to temperate rain forest to alpine areas. Climatic extremes can lead to natural selection on populations leading to adaptation, improved survival and reproduction in local environments. To guide the movement of appropriate plant materials in restoration and reforestation, seed zones have been developed. Seed zones separate areas by plant performance and/or climatic conditions important to plant growth, survival, and reproduction. To examine if populations are locally adapted, we used a reciprocal transplant experiment to investigate the efficacy of seed zones for bluebunch wheatgrass (Pseudoroegneria spicata). Bluebunch wheatgrass is an ecologically important restoration species for western North America. In the Interior Northwest U.S., we established 14 common garden sites in regions with different environmental conditions along two transects. Within a transect, each common garden site represents a seed zone. Each site was planted with four to five populations representing the local seed zone and four to five populations representing six other seed zones for a total of 34 populations. Each population was planted with 20 replicate seedlings. Common gardens were visited twice each growing season in 2015 and 2016 and once in 2017 recording survival, growth, phenology, and leaf morphology.
Across all sites, first-year survival was 80% and reduced in the second year to 59%. Plant survival and reproductive phenology differed among common garden sites, but there was no statistical difference in these traits between plants from local and non-local seed zones. Plant growth differed among common garden sites and by the source of the plant material with local plants having greater growth than non-local plants. Likewise local plants produced more reproductive stalks than non-local plants though the number of reproductive stalks produced per plant varied among common garden sites. Together these data support that bluebunch wheatgrass is locally adapted to climate. Since bluebunch wheatgrass is a perennial plant that can live for decades, the first three years is a glimpse into understanding how observed variation will affect long-term survival and fitness. Therefore the use of seed zones to guide restoration efforts will facilitate restoration success in that genetically appropriate plant material that is adapted to the local climate is used in restoration that will enhance plant population establishment and growth. The results of this study will help land managers to determine sources of bluebunch wheatgrass that can be used for post-fire restoration.