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Olszyk, David M., Claudia Wise, E. VanEss, and D.T. Tingey. 1998. Elevated temperature but not elevated CO2 affects stem diameter and height of Douglas-fir seedlings: results over three growing seasons. Can. J. For. Res. 28:1046-1054.

Global climatic changes may impact forest productivity over the next century, but data are lacking on potential effects of elevated temperature and CO2 on tree growth. Thus we determined changes in stem diameter and height for Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] seedlings with ambient or elevated CO2 (+200 mol mol-1) and/or ambient vs. elevated temperature (+4 C). Seedings were grown for three complete seasons in outdoor, sun-lit chambers, with a wet-dry season cycle of soil moisture and reliance on soil biological processes for nutrients. Stem diameter and height initiated and ceased growth earlier for elevated compared to ambient temperature trees. By the end of the third season, elevated temperature resulted in lower shoot heights (p<0.001), at 0.757 m for elevated vs. 1.016 m for ambient temperature trees; but did not affect stem diameter (average of 0.024 m across treatments). Elevated CO2 had no effect on stem diameter or height, and there was no evidence for any CO2 x temperature interactions. Thus, at least during early growth under field-like soil moisture and fertility conditions, elevated temperatures (but not elevated CO2) associated with climate change may shift allocation of aboveground biomass to stems, with implications for competition during seedling establishment and modeling tree growth.

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