PARENT SESSION
Oral Session # 40: Fire Ecology II: Forests.
Presiding: D Falk
Wednesday, August 6. 8:00 AM to 11:30 AM, SITCC Meeting Room 102.
Fuel structures and fire behavior in pinyon-juniper woodlands: Contrasting low vs. high density understory scenarios.
Balice, Randy *,1, Breshears, David2, 1 Ecology Group, Los Alamos, New Mexico, USA2 Atmospheric, Climatic and Environmental Dynamics Group, Los Alamos, New Mexico, USA
ABSTRACT- Pinyon-juniper woodlands, one of the most extensive forest types in the western USA, can pose substantial fire risks from hot burning crown fires, highlighted by large extensive fires in summers of 2002. Despite these risks, data on fuel structure in pinyon-juniper woodlands is largely lacking, particularly with respect to changes in the amount of tree canopy cover, as well as predictions of fire behavior associated with fuel structure. Our objectives were to (1) measure fuel structure in pinyon-juniper woodlands that ranged from low to high amounts of tree canopy cover, (2) to compare measured fuel structures with the baseline used in fire models (e.g. BEHAVE), and (3) to predict fire behavior as a function of wind speed and 1-hr moisture the measurements of fuel structure. We estimated fuel pinyon-juniper models from 14 plots in northern New Mexico. These results, which reflect low density understory conditions, are 50 to 90 percent less than values for published fuel models, which assume high density understory conditions associated with shrubs. The low-density understory condition produces lower rates of fire spread and probability of crown fire than the high understory conditions. Using our estimated fuel models as inputs to fire behavior models resulted in continuous canopy fires for windspeeds of 50 miles/hour and greater. Lower windspeeds propagated fires on the ground or fires that burned intermittently in the canopies. These results assume that fuels are continuous across the landscape. Actual fire behaviors may be strongly influenced by the interspersion of three pinyon-juniper fuel elements; trees with litter on the ground surface, intercanopy gaps with grasses and forbs, and intercanopy gaps with bare ground. Hence, our results highlight the importance of factoring in understory conditions in evaluating fire behavior for extensive pinyon-juniper woodlands.
Key words: fuels, pinyon-juniper woodlands, fire behavior