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, 96 (7), 1199-214

Genecology of Douglas Fir in Western Oregon and Washington


Genecology of Douglas Fir in Western Oregon and Washington

J Bradley St Clair et al. Ann Bot.


Background and aims: Genecological knowledge is important for understanding evolutionary processes and for managing genetic resources. Previous studies of coastal Douglas fir (Pseudotsuga menziesii var. menziesii) have been inconclusive with respect to geographical patterns of variation, due in part to limited sample intensity and geographical and climatic representation. This study describes and maps patterns of genetic variation in adaptive traits in coastal Douglas fir in western Oregon and Washington, USA.

Methods: Traits of growth, phenology and partitioning were measured in seedlings of 1338 parents from 1048 locations grown in common gardens. Relations between traits and environments of seed sources were explored using regressions and canonical correlation analysis. Maps of genetic variation as related to the environment were developed using a geographical information system (GIS).

Key results: Populations differed considerably for adaptive traits, in particular for bud phenology and emergence. Variation in bud-set, emergence and growth was strongly related to elevation and cool-season temperatures. Variation in bud-burst and partitioning to stem diameter versus height was related to latitude and summer drought. Seedlings from the east side of the Washington Cascades were considerably smaller, set bud later and burst bud earlier than populations from the west side.

Conclusions: Winter temperatures and frost dates are of overriding importance to the adaptation of Douglas fir to Pacific Northwest environments. Summer drought is of less importance. Maps generated using canonical correlation analysis and GIS allow easy visualization of a complex array of traits as related to a complex array of environments. The composite traits derived from canonical correlation analysis show two different patterns of variation associated with different gradients of cool-season temperatures and summer drought. The difference in growth and phenology between the westside and eastside Washington Cascades is hypothesized to be a consequence of the presence of interior variety (P. menziessii var. glauca) on the eastside.


F<sc>ig</sc>. 1.
Fig. 1.
Study area and locations of parents (grey dots).
F<sc>ig</sc>. 2.
Fig. 2.
Relation between the first canonical variable for traits (TRAIT1) and elevation of parent trees.
F<sc>ig</sc>. 3.
Fig. 3.
Geographical variation in (A) the first and (B) the second canonical variables for traits (TRAIT1 and TRAIT2, respectively). Mean values are shown as the zero contour between yellow and light green. Contour intervals represent a 30 % level of risk of maladaptation from source movement.
F<sc>ig</sc>. 4.
Fig. 4.
Geographical variation in traits of (A) first-year bud-set, (B) rate of emergence, (C) total weight, (D) root-to-shoot ratio, (E) second-year bud-burst and (F) taper. Mean values are shown as the contour between yellow and light green. Contour intervals represent a 30 % level of risk of maladaptation from source movement.
F<sc>ig</sc>. 5.
Fig. 5.
Map of areas of similar genetic types derived from overlaying the first and second canonical variables for traits.
F<sc>ig</sc>. 6.
Fig. 6.
Maps of residuals from the model developed for (A) first and (B) second canonical variables for traits as a function of the environment. The magnitude and sign of the residual are indicated by the relative size of the open (positive) or closed (negative) circle for individual source locations. A kriging function in ARC/INFO was used to interpolate between source locations.
F<sc>ig</sc>. 7.
Fig. 7.
The first canonical correlation for traits (TRAIT1) as related to elevation and December average daily minimum temperature for sources on the eastside and westside Washington and Oregon Cascades.

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