| dc.description.abstract | To help clarify the taxonomy of the two closely related North American firs
subalpine fir {Abies lasiocarpa (Hook.) Nutt.) and balsam fir {Abies balsamea
(L.) Mill.) in western Canada and the United States, 10 populations of
subalpine fir from Yukon Territory, northern British Columbia, and Alaska were
compared on the basis of morphological traits to fir populations from
Washington to northern Ontario. Principal components and discriminant
analyses were carried out separately on cone and needle data for various
subsets of these populations. Multiple regression analysis and analyses of
variance were used to investigate which evolutionary processes may have
been important in the recent development of subalpine fir at its northern
extreme. The regression analyses and analyses of variance suggest that
variation is expressed primarily within populations, throughout a single large
genepool at the northern extreme of subalpine fir's range, and that selection
due to local environmental pressures has produced the existing morphological
variation among populations. The multivariate analyses of cone and needle
data produced different results for several of the population subsets, indicating
that vegetative and sexual features of these firs respond to different selection
pressures at the various sites. Although the results are not entirely consistent,
the combined cone and needle data indicate that 1) north coastal British
Columbia and interior Rocky Mountain populations of subalpine fir are
generally distinct with the exception of a Vancouver Island population; 2)
northern subalpine fir populations exhibit an affinity to interior populations and
are very distinct from coastal populations. Additional geographic trends are 1)
two Washington Cascades subalpine fir populations are distinct from all other
populations in needle morphology, but one of these populations (Mount Baker)
is similar to the interior populations in cone morphology: 2) all balsam fir
populations are indistinguishable from interior subalpine fir populations on the
basis of needle morphology, but well-differentiated from these and coastal
populations in cone morphology. These results support 1) continued
recognition of subalpine and balsam fir as separate species and 2) recognition
of coastal and interior subalpine fir as separate taxa, perhaps at varietal rank.
The present results refute the theory that subalpine fir survived the Wisconsin
glaciation in one or more northern refugia. Rather, the close affinity between
northern and interior subalpine fir populations suggests that they originated
from a common Rocky Mountain refugium. | |
