Geographic variation in growth and phenology of seedlings of the Abies procena/A. magnifica complex

Abstract

Seedlings whose source origins extended over 12° of latitude (about 1300 km), 1800 m of elevation, and 250 km of longitude were grown for three years at Corvallis, Oregon, U.S.A. The sampled area included an interfertile complex of taxa, noble fir (Abies procera Rehd.), Shasta red fir (A. magnifica var. shastensis Lemm.) and California red fir (A. magnifica A. Murr.) from north to south. Size and phenological traits were measured in a common garden test, and analyzed to investigate the pattern of geographic variation.Division of the complex into three regions accounted for essentially all the latitudinal variation and strongly indicated a stepped cline. Elevation and longitude contributed lesser amounts of source variation. Lack of fit to the regression model indicated that other local factors also were important.Change in mean elevation of the sample sites with latitude was linear and closely followed Hopkins' ‘bioclimatic law’. Northern sources had the greatest relative elongation rates. Source variation within taxa was smaller than for comparable geographic ranges of some other western conifers. Based on field observations Shasta fir had been regarded as highly variable, but in this test its genetic variability was not greater than that of noble and California red firs. Genetic variance, estimated from families-in-locations and based on seedling traits, indicated ample opportunity for genetic gain.