Location: Range and Livestock ResearchTitle: Plains Prickly Pear Response to Fire: Effects of Fuel Load, Heat, Fire Weather, and Donor Site Soil Author
Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2011
Publication Date: 5/1/2011
Citation: Vermeire, L.T., Roth, A.D. 2011. Plains Prickly Pear Response to Fire: Effects of Fuel Load, Heat, Fire Weather, and Donor Site Soil. Rangeland Ecology and Management. 64:404-413. Interpretive Summary: Plains prickly pear mortality was related to fuel load and all measures of heat. The best predictor of mortality was duration of heat greater than 60oC. Because heat measures are often difficult to measure during fire, fuel load could be a good metric for developing fire prescriptions. Fire at any fuel load reduced plains prickly pear, but a threshold was identified between 1 500 and 3 000 kg*ha**-1, with live mass decreasing sharply between these fuel loads. Plains prickly pear were not uniquely acclimated to fire based on the soils where they originated. Variable responses of prickly pear across soils types would likely reflect changes in fuel load or fuel structure rather than ecological adaptation. Fire weather effects were minor despite considerable differences in ambient temperature and relative humidity. A gradient of wind effects was not evaluated, but could be important to the extent that wind affects duration of heat. The lack of ambient temperature and relative humidity effects suggests prickly pear control can be achieved under broad fire prescriptions as long as the amount of combustible fuel is adequate.
Technical Abstract: Plains prickly pear (Opuntia polyacantha Haw.) is common throughout the Great Plains and like related species, often becomes detrimental to agricultural production. We examined direct fire effects on plains prickly pear and mechanisms of tissue damage to facilitate development of fire prescriptions. Cladodes from clones on three soils (claypan, gravelly, silty) were subjected to fire with two weather conditions (moderate, severe) at four fuel loads (1 500, 3 000, 4 500, and 6 000 kg'ha-1) and a nonburned control. Fire was simulated with field-collected grass and heat was measured using thermocouples at the soil surface and 8 cm above. Plants were maintained in a greenhouse and monitored for cladode mortality or growth. Cactus response to fire was examined in a field experiment with four nonburned and four summer-burned 0.75-ha plots. Some plants from each treatment sprouted new cladodes. Soil of origin and fire weather effects were limited to mass of new sprouts as they interacted with fuel load. Fire under any condition reduced cactus mass and survival. Reduction in cactus mass increased from 42% with 1 500 kg*ha**-1 to 92% with fuel loads of 3 000 kg*ha**-1 or more. Fuel load, duration of heat, maximum temperature, and degree-seconds were each positively related to mortality, but duration of heat greater than 60oC was the best predictor. Plant mortality was 15% in the field, but number of live cladodes was initially reduced 91%. After one year, number of live pads in burned plots was 43% of that in nonburned plots because burned plants sprouted more new cladodes than nonburned plants. Insect and browsing damage occurred on 83% of cladodes in burned plots and only 8% for nonburned plots. Lack of fire weather effects suggests prickly pear control can be achieved under broad fire prescriptions, given the amount of combustible fuel is adequate.