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

摘要

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.