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Same-Age Growth Rates of Currently Old and Young Spruce Trees
Girard, F., Payette, S. and Gagnon, R. 2011. Dendroecological analysis of black spruce in lichen-spruce woodlands of the closed-crown forest zone in eastern Canada. Ecoscience 18: 279-294.

What was done
Working within lichen woodlands of the forest zone of Eastern Canada between longitudes 70 and 72°W, the authors acquired data that enabled them to calculate radial, height and volume growth rates at every 15 minutes of latitude from 47°30'N to 52°41'N for black spruce (Picea mariana) trees ranging in age from 34 to 188 years.

What was learned
Dividing the trees into a young group and an old group, with ages ranging between 34 and 93 years for the young group and between 109 and 188 years for the old group, Girard et al. determined that same-age "radial, height and volume growth rates of trees in stands younger than 100 years were 46%, 51% and 38%, respectively, greater than those of trees in stands older than 100 years." And for the two youngest stands with mean ages of 34 and 43 years, they found that "black spruce showed radial, height and volume growth rates of 66%, 74% and 71%, respectively, greater than those in woodlands older than 100 years."

What it means
In discussing their findings, the three Canadian researchers cite other studies that demonstrate that "tree productivity in northern forests of eastern North America has increased significantly since the middle of the 19th century," namely, Payette et al. (1985), D'Arrigo et al. (1987), D'Arrigo et al. (1992) and Lavoie and Payette (1994). In addition, they say that "similar trends have been observed in the American West," citing Graumlich et al. (1989) and Peterson et al. (1990). And we note that in our Editorial of 23 February 2011, we cite seven additional studies that have observed the same phenomenon in "numerous tree species in a variety of climatic regions." And we cite various studies that point to the historical increase in the air's CO2 content as the primary cause of this great increase in the growth of woody species over the course of the 20th century and the early stages of the 21st century.

D'Arrigo, R., Jacoby, G. and Free, R. 1992. Tree-ring width and maximum latewood density at the North-American tree line: Parameters of climatic change. Canadian Journal of Forest Research 22: 1290-1296.

D'Arrigo, R., Jacoby, G. and Fung, I. 1987. Boreal forests and atmosphere biosphere exchange of carbon dioxide. Nature 329: 321-323.

Graumlich, L.J., Brubaker, L.B. and Grier, C.C. 1989. Long-term trends in forest net primary productivity: Cascade Mountains, Washington. Ecology 70: 405-410.

Lavoie, C. and Payette, S. 1994. Recent fluctuations of the lichen spruce forest limit in subarctic Quebec. Journal of Ecology 82: 725-734.

Payette, S., Filion, L., Gauthier, L. and Boutin, Y. 1985. Secular climate change in old-growth treeline vegetation of northern Quebec. Nature 315: 135-138.

Peterson, D.L., Arbaugh, M.J., Robinson, L.J. and Derderian, B.R. 1990. Growth trends of whitebark pine and lodgepole pine in a sub-alpine Sierra-Nevada forest, California, USA. Arctic and Alpine Research 22: 233-243.

Reviewed 11 April 2012