Nitrogen Losses to the Atmosphere From Grassland Fires in Saskatchewan, Canada

Abstract

Experimental spring fires burned 72-84% of the biomass in Saskatchewan grasslands dominated by either Festuca altaica ssp. hallii (Plains rough fescue) or Stipa spartea (Western porcupine grass) and Agropyron dasystachyum (Northern wheatgrass). Festuca stands had more fuel, and a higher combustion efficiency than Stipa-Agropyron sites. Burning decreased total nitrogen by 3.7-6.7 g m^-2 in Festuca grassland; nitrogen content of Stipa-Agropyron stands was not decreased significantly by burning. Indirect evidence (black ash color) suggested that fire temperatures were lower in Stipa-Agropyron stands. Controlled combustion experiments in the laboratory showed that 40-60% of tissue nitrogen was lost from Festuca shoots exposed to 300-400°C for three minutes. Losses of nitrogen from Festuca grassland are approximately equal to or greater than published values for annual inputs and outputs of nitrogen in grassland ecosystems, depending on fire frequency.