Seed zones for maintaining adapted plant populations

Seed zones delineate areas within which plant materials can be transferred with little risk that they will be poorly adapted to their new location. They ensure successful restoration and revegetation, and help maintain the integrity of natural genetic structure. The value of seed zones is recognized in numerous policy statements from federal and state agencies. Results from common garden studies indicate that local sources are often best adapted to local environments, although the degree of local adaptation differs between species and between traits within species. Seed zones have been used for over 60 years in forest trees, whereas seed zones for grasses, forbs and shrubs used in restoration are largely lacking. We discuss several studies that have been completed or initiated to study adaptive genetic variation and the development of seed zones in species widely used in restoration in the western United States.