Adaptive variation of trembling aspen in Northwestern Ontario
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To demonstrate the pattern of adaptive variation of Populus tremuloides (Michx.) to northwestern Ontario climate conditions, a statistical analysis was completed of growth and phenology variables from 26 provenances. Growth variables included: height measured in 1999, 2000, 2003 and 2004; stem diameter measured in 1999, 2000 and 2002; leader length measured in 2000; and, leaf flushing measured in 2000. Adaptive variation was summarized by four principal component (PC) axes modeled by climate variables at seed origin that explained 41.5, 15.8, 10.0 and 6.3 percent of the growth and phenology variation among provenances. A clinal pattern of adaptive variation in leaf flushing predicted by temperature in the growing season was demonstrated by the first PC axis. The second PC axis was strongly influenced by growth data at one test site (Dog River) and showed a weak latitudinal trend related to winter temperature and precipitation at the start of the growing season. A longitudinal pattern of adaptive variation in growth and chlorophyll florescence variables predicted by July precipitation was demonstrated in PC axis 3. A latitudinal trend was shown for PC axis 4 where adaptive variation was expressed through a combination of winter temperatures and June mean temperature that predicted leader length and height potential together with October frost hardiness. The pattern of adaptive variation indicated significant genetic variation among trembling aspen provenances over a relatively small region.