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Black Cottonwood Trees of Alberta, Canada
References
Berg, K.J., Samuelson, G.M., Willms, C.R., Pearce, D.W. and Rood, S.B. 2007. Consistent growth of black cottonwoods despite temperature variation across elevational ecoregions in the Rocky Mountains. Trees 21: 161-169.

Rood, S.B., Berg, K.J. and Pearce, D.W. 2007. Localized temperature adaptation of cottonwoods from elevational ecoregions in the Rocky Mountains. Trees 21: 171-180.

Background
Climate alarmists have long claimed that CO2-induced global warming - if it ever really "takes off" - will be so fast and furious that many species of plants will not be able to migrate poleward in latitude or upward in altitude fast enough to escape extinction, if the climate significantly changes from that to which they are accustomed.

What was done
Berg et al. analyzed annual growth rings of 167 black cottonwood (Populus trichocarpa Torr. & Gray) trees growing along two creeks in the Rocky Mountain region of Alberta, Canada, while in the laboratory Rood et al. studied the growth responses to temperature of saplings of 14 cottonwood genotypes that they generated from stem cuttings of trees from three distinct ecoregions along the elevational gradient of the two streams: an upper montane region, an intermediate aspen parkland, and a lower fescue prairie region.

What was learned
Berg et al. found that despite a 3.8C June-December mean temperature difference between the fescue prairie and montane zones, which led to a 42% increase in growing degree days when gong from the montane zone to the fescue prairie zone, the "growth rate of most trees was fairly consistent across the ecoregions," such that "there was only about an 11% difference in the typical trunk diameter of century-old black cottonwoods across [the] three mountain zone ecoregions," according to Rood et al. In addition, the work of the latter researchers demonstrated the existence of what they call "localized temperature adaptation" and "elevational ecotypes of black cottonwood," which they say is "consistent with results from studies of other deciduous and coniferous trees along mountain profiles (Sparks and Ehleringer, 1997; Oleksyn et al., 1998; Weih and Karlsson, 1999)."

What it means
The findings of Berg et al. and Rood et al., augmented by the similar observations of the other researchers they cite, suggest that the black cottonwood trees of Alberta, Canada, are indeed ready for whatever nature might throw at them in the way of continued global warming, having the capacity to migrate upward in altitude without having to necessarily give up ground at lower elevations, as their existent genotypes appear to exhibit a wide range of adaptability to temperature.

References
Oleksyn, J., Modrzynski, J., Tjoelker, M.G., Zytkowaik, R., Reich, P.B. and Karolewski, P. 1998. Growth and physiology of Picea abies populations from elevational transects: Common garden evidence for altitudinal ecotypes and cold adaptation. Functional Ecology 12: 573-590.

Sparks, J.P. and Ehleringer, J.H. 1997. Leaf carbon isotope discrimination and nitrogen content for riparian trees along elevational transects. Oecologia 109: 362-367.

Weih, M. and Karlsson, P.S. 1999. Growth response of altitudinal ecotypes of mountain birch to temperature and fertilization. Oecologia 119: 16-23.

Reviewed 11 July 2007