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Submitted to: Fire Ecology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/14/2014 Publication Date: 7/17/2014 Citation: Augustine, D.J., Derner, J.D., Smith, D.P. 2014. Characteristics of burns conducted under modified prescriptions to mitigate limited fuels in a semi-arid grassland. Fire Ecology. 10(2):36-47. Interpretive Summary: In rangelands of the western Great Plains, fire has traditionally been viewed as having few management uses, and little is known about fire behavior in this area of the country. More recently, land managers been using prescribed fire to control undesirable rangeland plants and to manage habitat for wildlife in this region. We conducted a series of prescribed fires in rangelands of northeastern Colorado, and collected measurements of fire temperatures and how long high temperatures persisted during fires. We used these measurements to examine how fuel loads (amount of dead grass) and weather conditions affect fire intensity. We found that fires did not spread successfully when fuel loads were less than 350 kg/ha (313 lb/acre). When burns were conducted with fuel loads above this threshold, we found that fire intensity was 1) lower than reported for mixed grass prairies, 2) primarily influenced by variation in fuel loads, and 3) secondarily influenced by wind speed, ambient air temperature, and relative humidity. We present models that predict heat production during prescribed fires in shortgrass steppe. Based on these models, we provide suggestions for burn prescriptions to achieve goals such as reducing abundance of prickly pear cactus and broom snakeweed and providing habitat for native birds such as the mountain plover. Technical Abstract: In semiarid grasslands of the North American Great Plains, fire has traditionally been viewed as having few management applications, and quantitative measurements of fire behavior in the low fuel loads characteristic of this region are lacking. More recently, land managers have recognized potential applications of prescribed fire to control undesirable plant species and to manage habitat for wildlife in this region. Working in the shortgrass steppe of northeastern Colorado over a 7-year period, we quantified peak temperatures, heating duration, and heat dosage produced near ground level during prescribed burns conducted under a wide range of fuel loads and weather conditions. We use an information theoretic approach to develop models that predict peak temperature and heat dosage as a function of weather parameters and fuel loads. We conducted successful burns (>80% of target area burnt) with fuel loads varying from 350 – 1175 kg ha-1, while burns with fuel loads <350 kg ha-1 generally failed to spread and burned less than 60% of target areas. Peak temperatures, heat duration and heat dosage during shortgrass burns were 1) lower than reported for mixed-grass prairies, 2) primarily influenced by variation in fuel loads, and 3) secondarily influenced by wind speed, ambient air temperature, and relative humidity. Compared to desert grassland, heat doses near the ground surface were similar, but peak temperatures were lower and heat duration longer in shortgrass steppe burns. Our findings provide quantitative predictions for heat production from fires in shortgrass steppe near the ground surface, where most plant meristems are located. Based on these relationships, we provide suggestions for burn prescriptions to achieve goals such as reducing abundance of prickly pear cactus (Opuntia polyacantha) and broom snakeweed (Gutierrezia sarothrae) and providing habitat for native birds such as the mountain plover (Charadrius montanus). |
