Combustion properties of Bromus tectorum L.: influence of ecotype and growth under four CO2 concentrations
Robert R. Blank A D , Robert H. White B and Lewis H. Ziska CA USDA Agricultural Research Service, Exotic and Invasive Weed Research Unit, 920 Valley Road, Reno, NV 89512, USA.
B USDA Forest Service, Forest Products Laboratory, One Gifford Pinchot Drive, Madison, WI 53726-2398, USA.
C Alternate Crops and Systems Lab, USDA Agricultural Research Service, Beltsville, MD 20705, USA.
D Corresponding author. Email: blank@unr.nevada.edu
International Journal of Wildland Fire 15(2) 227-236 https://doi.org/10.1071/WF05055
Submitted: 19 May 2005 Accepted: 1 December 2005 Published: 31 May 2006
Abstract
We grew from seed the exotic invasive annual grass Bromus tectorum L., collected from three elevation ecotypes in northern Nevada, USA. Plants were exposed to four CO2 atmosphere concentrations: 270, 320, 370, and 420 μmol mol–1. After harvest on day 87, above-ground tissue was milled, conditioned to 30% relative humidity, and combustion properties were measured using a cone calorimeter. Plants exposed to 270 μmol mol–1 CO2 had significantly less total heat released than plants exposed to higher CO2 concentrations. Total heat released was least for the low-elevation ecotype, statistically similar for the mid-elevation ecotype, and significantly increased for the high-elevation ecotype. Plant attributes that significantly correlated with heat release included tissue concentrations of lignin, glucan, xylan, potassium, calcium, and manganese. The data suggest that a decline in tissue concentrations of lignin, xylan, and mineral constituents, as CO2 concentration increases from 270 μmol mol–1 to higher levels, affects the combustion process. We suspect that as tissue concentrations of lignin and inorganics decline, char formation decreases, thereby allowing more complete combustion. Changes in combustion parameters of B. tectorum induced by different CO2 concentrations and elevation ecotype may be a strong consideration to understanding fire behaviors of the past, present, and future.
Additional keywords: char; flammability; global change; lignin; wildfire.
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