Download Soil Characteristics Across Burn Severities in the Las Conchas Fire

Soil Characteristics Across Burn Severities in the Las Conchas Fire
Elyssa Duran, Anita Lavadie, Sara Brown, Joseph Zebrowski, Edward Martinez, New Mexico Highlands University Las
Vegas, NM
Abstract—Climate change is currently one of the major drivers of increasingly severe wildland fire behavior
throughout the Southwest. The Las Conchas fire in the Jemez Mountains, New Mexico, burned during the
summer of 2011. It was the largest recorded fire in the state until it was surpassed in size the following year
by the Whitewater-Baldy complex. Las Conchas provided an excellent opportunity to study fire effects on
soil nutrient concentrations in differing fire severities, as small fluctuations in nutrients can have major implications on water quality and vegetation recovery. We collected and analyzed soils for texture, potassium
(K), aluminum (Al), manganese (Mn), ammonium (NH4), iron (Fe), copper (Cu), pH, nitrate-nitrogen (NO3-N)
and orthophosphate (PO4). Soil samples were collected from five plots in each of the four fire severities
types: control (unburned) and low, moderate, and high. Each of the sites is similar in parent material and
vegetation. We analyzed soil texture using the bouyoucos hydrometer method, and nutrient levels [excluding
(NO3-N) and (PO4)] were analyzed using LaMotte Soil Nutrient Kits. NO3-N and PO4 levels were measured
using an Analytical FS 3100 Automated Chemistry Analyzer following USEPA method 353.2. The soil texture
at all four sampling sites was classified as a sandy loam. There were no significant differences between any
of the fire severity sites or the control for K, Al, Mn, NH4, Fe, Cu or pH using the LaMotte Kits. Our findings
suggest that NO3-N and PO4 concentrations in soil decreased with an increase in fire severity. Low concentrations of NO3-N and PO4 were found at all study sites: low severity (1.5 (µg/g) NO3-N; 0.27 (µg/g) PO4),
moderate severity (1.3 (µg/g) NO3-N; 0.22 (µg/g) PO4, high severity (0.6 (µg/g) NO3-N; 0.12 (µg/g) PO4)
and control (unburned)(3.0 (µg/g) NO3-N; 0.11 (µg/g) PO4). Heavy monsoonal precipitation events after the
containment of the Las Conchas fire initiated major movement of soil especially in the severely burn areas.
This mass movement of soil partially explains the low concentrations of NO3 –N in the burned area, and
may have facilitated the availability of PO4 due to the unearthing of parent material. In the unburned site,
the decreased concentration of PO4 as compared to the burned plots could likely be explained by utilization
through biological processes. Higher concentrations of NO3 –N in the unburned control site compared to the
burned sites may also be explained by summer rain facilitating mineralization through microbial processes.
Additional research examining soil nutrient dynamics post fire needs to be undertaken in uncharacteristically
large, severe fires to better understand the impacts on vegetation recovery.
Keywords: Soil, NO3, PO4, Fire, Las Conchas, Climate Change, Fire Severity
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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