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Effects of a Warming Climate on Western U.S. Sagebrush
Reference
Perfors, T., Harte, J. and Alter, S.E. 2003. Enhanced growth of sagebrush (Artemisia tridentata) in response to manipulated ecosystem warming. Global Change Biology 9: 736-742.

Background
Since 6 January 1991, a set of overhead infrared radiative heaters have been continuously warming five 3- x 10-meter plots of ungrazed montane meadow at the Rocky Mountain Biological Laboratory in Gunnison County, Colorado, USA, while five similar plots have served as controls. The extra downward flux of infrared radiation warms the top 15 cm of soil by about 1.5C and dries it by about 15% on a gravimetric basis during the growing season, prolonging the snow-free season at each end by a total of about 20 days.

What was done
The authors developed and applied a method for extracting the age-detrended growth rate of common sagebrush -- Artemisia tridentata (Nutt.), ssp. vaseyana -- a perennial shrub that is abundant throughout much of the semiarid western United States, in an effort to determine the effect of a modest warming on the distribution of this common woody plant.

What was learned
Annual sagebrush growth rates in the heated plots were approximately 50% greater than those in the control plots, due primarily to the warming-induced increase in the length of the snow-free season.

What it means
The authors say their observations and analysis "suggest that global climate change, which is expected to result in a contracted period of snow accumulation in the montane west, will result in increased growth and range expansion of sagebrush near high-elevation range boundaries in the western US." Although it had earlier been demonstrated that the experimental warming treatment decreased soil organic carbon content (Saleska et al., 2002), Perfors et al. further suggest that, over the long haul, "because sagebrush litter is more recalcitrant to decomposition than is the litter from the forb species that are in decline in the heated plots of our climate manipulation experiment, enhanced sagebrush growth could also contribute to a negative feedback [to CO2-induced warming] by increasing the turnover time of soil carbon."

Reference
Saleska, S.R., Shaw, M.R., Fischer, M.L., Dunne, J.A., Still, C.J., Holman, M.L. and Harte, J. 2002. Plant community composition mediates both large transient decline and predicted long-term recovery of soil carbon under climate warming. Global Biogeochemical Cycles 16: 10.1029/2001GB001573.


Reviewed 23 July 2003