Stochastic Fire Modeling of a Montane Grassland-Forest Landscape in the Valles Caldera National Preserve, New Mexico, USA

Abstract

Montane ecosystems of the western United States have experienced dramatic changes in their fire regimes over the last 150 years. Fire behavior modeling enables understanding of how ecosystem changes have altered past fire regimes. The Valles Caldera National Preserve in the Jemez Mountains, northern New Mexico, contains one of the largest montane grasslands in North America. This area is used for multiple uses ranging from logging to grazing and recreation. These important ecosystems have experienced increased fuel loads and stem densities resulting from a century of fire exclusion and tree encroachment, resulting in potentially anomalous fire behavior. We investigated whether fire pathways tend to spread along the grassland-forest ecotone or if fire would spread directly across grasslands under extreme fire weather conditions. We used the program FlamMap to model fire behavior under a variety of weather and fuel conditions. Fire spread pathways and burn perimeters were computed for the 50th, 90th, and 99th percentiles of historic weather conditions. The results are compiled into a probability surface that represents the most parsimonious pathways of fire spread in this landscape. We found that pathways were related to the origin of ignition; fires tended to spread around the ecotone, facilitating fire spread to adjacent grasslands. These results, complemented with fire history studies in dendrochronology and empirical observations of the Las Conchas Fire in 2011, further the understanding of the role and dynamics of fire in maintaining the montane-grassland conifer ecotone, and can guide efforts to restore a landscape affected by the effects of fire exclusion.