| dc.description.abstract | The Abies section Nobilis Engelm. consists of two high-elevation
tree species that grow in the mountains of Washington, Oregon and
California. The two varieties of A.magnifica A.Murray grow south of
A.procera Rehd. One of these varieties, A.magnifica var.shastensis
Lemm., is intermediate in some characteristics and locations between the
two "typical" species. The goal of this thesis was to clarify species and
population differentiation in the section Nobiiis. To this end, nine
populations of mature and twelve populations of immature trees were
collected along a north-south transect that cut through most of the range
of the section. The flavonoids were extracted from dried needle samples
selected from each of the sample trees, and a flavonoid profile was
determined for each tree. These individual tree profiles were used to
prepare a composite flavonoid profile for the whole section.
Sixty-four probable flavonoid compounds occurred in the sample
trees, of which forty-seven were at least partially identified. Twenty-four
variable compounds were chosen for analysis. Variation was assessed
using product-moment correlation co-efficients, frequency histograms,
principal components analysis, weighted-pair-group cluster analysis,
discriminant analysis and cladistic analysis. These different statistical
techniques allowed comparison between the different interpretations of
population variation.
Four factors appear to underly the pattern of population variation in
the Abies section Nobilis : (1) evolution of the section under the diverse
and changing conditions that have prevailed in the Pacific Northwest and
California since the Oligocene epoch; (2) hybridization between
morphologically, ecologically and/or chemically differentiated populations
of trees within the section; (3) the presence of a genetically variable gene
pool in the section as a consequence of these two factors; and (4) the expression of a portion of that variability as adaptation to
different stages of forest succession.
A.procera is an early-successional species with a gene pool that
is more uniform than A.magnifica, which is essentially a late-succession
or climax species. Flavonoid differentiation between these two species is
not as distinct as has been observed in the Abies section Balsamea
Engelm. Aprocera tends to exhibit acetylated monoglycosides
consistently whereas A.magnifica does not, and A.magnifica tends to
accumulate glycosides of dihydrokaempferol and taxifolin where
A.procera does not. These differences apparently have been obscured
somewhat by variation between the flavonoid complement of mature and
immature trees, by migration and fragmentation of the range of the
section Nobilis since the Oligocene epoch, and by hybridization within
the section.
The needle flavonoid results reported by this thesis, supported by
published ecological, morphological and terpene data, confirm the current
recognition of three taxa in the section. However, the variety shastensis
exhibits enough differentiation to warrant further investigation into
separation of that taxon into three or four separate taxa: (^) A. procera x
A.magnifica; (2) relictual populations of A.magnifica var.shastensis
in Tulare County, California and the Klamath Mountains of California and
Oregon; and (3) A.magnifica var.shastensis from the North Coast
Ranges of California. | |
