Local variation in intergrading Abies grandis-Abies concolor populations in the central Oregon Cascades: needle morphology and periderm color

In the central Oregon Cascades, grand fir morphology varies from that of typical Abies grandis tothat of populations with a variety of morphological types, some closely resembling A. concolor. Low-elevation populations west of the Cascade crest, mostly on river terraces, resemble A. grandis. High-elevation west-side populations, disjunct from those at low elevations and occupying ridge tops and steep,dry slopes, include trees with some traits of A. concolor. Populations on the east flank of the Cascadesshow a greater but widely variable influence of A. concolor. East-side populations vary locally withaspect, being most like A. grandis on north slopes, but they do not clearly vary with elevation. Incidenceof characteristics resembling A. concolor increases from north to south within the study area, althoughthis pattern shows deviations not associated with obvious changes in topography. Periderm color andneedle morphology show the same general relationships between the populations sampled. Either "maxi-mum number of adaxial stomatal rows" or "percentage of length of needle with adaxial stomata" can beused to describe the extent of adaxial stomata. Needle notch depth is not consistently correlated withstomata( characteristics on a tree-to-tree basis, but shows a similar, less distinct, geographic and habitatpattern. The variation within populations is greater in the intermediate populations than in those of"typical" A. grandis. This is consistent with the origin of the intermediate populations being intro-gression, as proposed by earlier workers. The described patterns of morphological variation provide abasis from which ecological and physiological variation in these intergrading populations may be studied