Breeding zones associated with seed sources planted at each Experimental Network for Assisted Migration and Establishment Silviculture (ENAMES) field site. Seed sources come from areas reflecting historical (1961-1990), early-century (2011-2040), mid-century (2041 - 2070), and late-century (2071-2100) climate conditions at the planting site.

The breeding zone feature class was created from 500-foot digital elevation models across Region 6 (Oregon and Washington) of the USDA Forest Service, then aggregated into ‘generic’ or species-specific elevation bands as defined in each national forest Tree Improvement Plan/Guide to further limit seed movement within breeding blocks. Generic zones were defined for all forests.

The width of the breeding zones was guided by the geographic trends of genetic variation in different species and national forests, principally predicted from growing season length and risk of maladaptation to cold. Generally, the width of the breeding zone decreases with elevation. The upper and lower limits were determined by species distribution on Forest Service lands and sometimes extend above and below the species presence.