The Las Conchas Fire, New Mexico, in Historical Context
Sara Brown, Edward A. Martinez, Joseph P. Zebrowski, New Mexico Highlands University Las Vegas, NM
Abstract—Wildland fires have been increasing in spatial extent and severity in recent decades across the
western US. Our research team has spent the past two and a half years researching the broad range of fire
effects from one large, predominantly severe wildfire in the southwest region, the Las Conchas fire (2011) located in the Jemez Mountains of New Mexico (approximately 56% of the fire area was classified as moderate
or high severity). Our study sites are located in the Valles Caldera National Preserve, which was not impacted by fire retardant during suppression activities, and was not directly rehabilitated post-fire. Fortunately,
several fire history studies have been conducted near our study area, providing us with information about
historic fire regimes and climate-fire interactions. For the lower elevation ponderosa pine dominated forests,
fire scars indicate that low severity surface fires burned relatively frequently (5 to15 years). In the higher elevation mesic mixed-conifer dominated forest, fire return intervals were longer (15 to 30 years). Fire scarring
and recruitment dates indicate that both surface fire and patchy crown fires occurred in this forest type. Fires
historically burned between the months of April and September, with the largest fires burning in June before
the monsoonal moisture typically arrived in July. Large fire years were often synchronous with dry years
that followed two years after a significantly wet winter/spring in the ponderosa pine forests. Fuel moisture,
rather than fuel availability, was found to determine fire occurrence in the mesic mixed-conifer forests. The
once-frequent surface fires ceased around 1890 A.D. in this region of the Jemez Mountains due to coupling
of several landscape-level change agents: livestock grazing, fire exclusion and a reduction in fuels through
logging efforts. Intense sheep grazing began in the grassland areas on the Valles Caldera around 1748 A.D.
After a decline in wool prices in 1940 A.D., cattle and horse grazing increased. Grazing practices reduced the
fine fuels that would have carried historic surface fires, and prompted fire suppression in the area to protect
both grazing and timber profits. Logging operations began in 1926 A.D. and continued until around 1975
A.D., resulting in large areas of second-growth forest with tree densities of 800 to 2000 trees/acre. Historic
reference conditions for ponderosa pine in the southwest are 11.7 to124 trees/ac, and for mixed-conifer are
20.9 to99.4 trees/ac. Additional studies at the Valles Caldera suggest that between 1935 A.D. and 1965 A.D.
the grasslands decreased in size by 18 percent due to encroachment and infilling by conifers, leading to an
overall increase in fuel density and ladder fuels. These drivers of change partially explain the departure from
the historical range of variability in vegetation and fire regimes, and thus partially explain the fire severity
and behavior of the Las Conchas Fire.
Keywords: Fire History, Valles Caldera, Change Agents, Historic Range of Variability, Wildland Fire
In: Keane, Robert E.; Jolly, Matt; Parsons, Russell; Riley, Karin. 2015. Proceedings
of the large wildland fires conference; May 19-23, 2014; Missoula, MT. Proc.
RMRS-P-73. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky
Mountain Research Station. 345 p.
USDA Forest Service Proceedings RMRS-P-73. 2015.
The content of this paper reflects the views of the authors, who are responsible for the
facts and accuracy of the information presented herein.
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