A comparison of habitat type and elevation for seed-zone classification of Douglas-fir in western Oregon

Habitat type (identified by plant indicators) and elevation were compared as alter-native bases for stratifying forest land into breeding zones or seed zones for reforestation. Thecomparison was based on the assumption that the genetic variation in an indigenous populationof Douglas-fir (Pseudolsuga menziesii (Mirb.) Franco) reflects the adaptively important environ-mental variation in the area inhabited by the population. Relative values for habitat type andelevation were then estimated by the amount of genetic variation explained by each in classifi-cation and regression models. Elevations, habitat types and tree genotypes were sampled in a6100-hectare watershed in the Cascade Range of western Oregon. Parent trees (190) were from114 locations (sources) in the watershed. Genetic variation was estimated by the performance(in 15 traits) of 3-year-old seedling families (190) grown in a common garden. Neither elevationnor habitat type were completely satisfactory for classifying environments into zones, in thatelevation explained only about 56 percent of the source-related genetic variation, habitat typeonly about 35 percent.
ADDITIONAL KEY WORDS. Pseudot.suga menziesii. adaptation, genecology, plant indicators.