PARENT SESSION
Oral Sessions - Fire in Landscapes - Day 2 Chair(s): Wimberly, Michael¹, ¹ University of Georgia, Athens, GA
Friday, April 2, 2004 3:00 PM - 4:40 PM Apollo Room 8

Influences of landscape structure, drought, and wind on crown fire spread in forest landscapes. ^*WIMBERLY, MICHAEL C. ¹, AVERY, CHADWICK ¹, OHMANN, JANET L. ², PIERCE, KENNETH B. ², GREGORY, MATTHEW J. ³ and FRIED, JEREMY S. ⁴, ¹ Warnell School of Forest Resources, Athens, GA, USA² USDA Forest Service, Corvallis, OR, USA³ Oregon State University, Corvallis, OR, USA⁴ USDA Forest Service, Portland, OR, USA

ABSTRACT- Landscape ecology posits the existence of critical thresholds at which ecosystem structure and related processes respond rapidly to relatively small shifts in landscape composition. Such thresholds may influence the propagation of fire through heterogeneous landscapes, with mosaics of patchy fuels becoming connected when extreme weather renders many fuel types susceptible to crown fire. Although this hypothesis has been invoked to explain the occurrence of large disturbance events such as the Yellowstone fires of 1988, it has not yet been subjected to rigorous quantitative analysis. The availability of new models for predicting spatial patterns of fire behavior, along with new techniques for mapping forest fuels, now provide an opportunity to test for the presence of these critical thresholds. Our study area encompassed approximately 350,000 ha in the southern Oregon Coast Range We used the GNN (Gradient Nearest Neighbor) method to generate maps of canopy bulk density, height to canopy base, stand height, percent canopy cover, and Albini fuel models from forest plot data, Landsat TM imagery, and GIS databases. We then used the FLAMMAP model to map the potential for crown fire occurrence over a range of fuel moisture conditions and wind speeds, and analyzed the results using spatial metrics. The model predicted threshold responses of landscape-level fire behavior in response to both fuel moisture and wind. Once these variables reached a critical level, potential crown fire areas coalesced into a few large patches that connected large portions of the landscape. However, the existence of large hardwood stands and non-forest patches in this landscape constrained the potential for crown fire spread even under the most severe weather conditions.

KEY WORDS: fire, fuels, percolation, disturbance spread, connectivity