Fire History and Fire Effects of Mesa Verde National Park: Final Report

Floyd-Hanna, Lisa; Romme, William

Mesa Verde National Park supports, along with many other plant communities, large expanses of pinon-juniper woodland and mountain shrub communities. The spatial distribution of these communities, with a predominance of pinon pine and juniper on the south end of the mesas and mountain shrubs on the northern end, led us to hypothesize that frequent fires may be one factor controlling this pattern. The study of fire history and fire effects at Mesa Verde Park took place in 1991, 1992, and 1994 and had several objectives. One study determined the vegetation patterns which have resulted since the 1989 Long Mesa fire. This large fire impacted at least three different vegetation types, pifton-juniper woodland, mountain shrub stands, and the Douglas Fir-Shrub community found on the north escarpment. The second objective was to develop and apply a method of dating past fires in Mesa Verde. As few fire-scarring tree species occur in Mesa Verde National Park, we developed a method in which shrubs, which reprout vigorously after fires, were aged by annual ring counts to determine their time of origin. The third study involved evaluation of fuels in the recently-defined vegetation communities (Floyd-Hanna et al, 1994) throughout the park. Fuel models were developed using BEHAVE to predict possible fire regimes. A method was developed to date past fire disturbance using Quercus gambeliidonal ages. In the northwest section of the park, large fires were detected, dating to the 1850's, 1870's, 1880's, and 1910's. We completed the stand origin map of the northeastern section of the Park by dating oak clones from Moccasin Mesa to the eastern escarpment. Large stand replacing fires date in the 1860's, 1870's, 1880's, while smaller fires date within the 1890's and the 1900's. One small fire was detected in 1910, and several old patches exceeded our ability to resolve stand dates. The interval between fires varied from 21 years (1850-1875), 44 years (1875-1906, to 122 years (1906-present). In a related study, we defined 14 major vegetation communities in Mesa Verde Park. Here we report our efforts to sample woody fuels in these communities. Woody fuels data included down and standing fuels. These data were incorporated into custom fuel models using BEHAVE, a modeling program which predicts fire behavior under vaying fuel and site conditions. Finally, we determined the stand structure of pinon-juniper woodlands, focusing specifically on the possible origin these woodlands. Were the woodlands established by a rapid invasion following a catastrophic event, providing a uniform, old-aged structure? Or, are old trees uneven aged? We determined, in a pilot study, that sampled pinon-juniper woodlands are uneven aged with adult pinon pines reaching 370 years and adult junipers reaching 500 years of age.