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Comparison of the Higher-Severity Fire Regime in Historical (A.D. 1800s) and Modern (A.D. 1984–2009) Montane Forests Across 624,156 ha of the Colorado Front Range

Research paper by Mark A. Williams, William L. Baker

Indexed on: 12 May '12Published on: 12 May '12Published in: Ecosystems (New York, N.Y.)



Abstract

There are concerns that recent fires, following a century of land uses, are burning in dry western forests in an uncharacteristic manner with large patches of higher-severity fire affecting long-term ecosystem dynamics. For example, it is well documented that a mixed-severity fire regime predominated over montane forests of the Colorado Front Range. However, much about the historical fire regime is unknown including the size, frequency, and distribution of higher-severity fires. We addressed these questions utilizing data from the original land surveyors who recorded locations of burned timber along survey lines resulting in a coarse-scale transect of fire occurrence across 624,156 ha. We reconstructed higher-severity burn patches, size distribution, and fire rotation for the 1800s (A.D. 1809–1883) and compared to the characteristics of modern fires over a recent 26-year period (A.D. 1984–2009) taken from remotely sensed data. We found the historical geometric mean higher-severity patch was 170.9 ha and the maximum patch size was 8,331 ha; the higher-severity fire rotation was 248.7 years. In addition, we confirmed that higher-severity fires were historically less common at elevations below 2,200 m. Modern fires had a geometric mean patch size of 90.0 ha (patches >20 ha) and a maximum size of 5,183 ha; the higher-severity fire rotation was 431 years. The distributions of higher-severity patches were only 63.5% similar, as the historical distribution had fewer small patches and more large patches. The mixed-severity fire regime, historically, included a significant portion of higher-severity fire and large burn patches; modern fires appear to be within the range of historical variability.