Toward reference conditions: wildfire effects on flora in an old-growth ponderosa pine forest |
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| Affiliation: | 1. Ecological Restoration Institute, Northern Arizona University, P.O. Box 15017, Flagstaff, AZ 86011, USA;2. Dolores Public Lands Office, P.O. Box 210, Dolores, CO 81323, USA;3. Department of Forestry, Rangeland and Watershed Stewardship, Colorado State University, Fort Collins, CO 80523, USA;1. Department of Mathematics, Oregon State University, Corvallis, OR 97330, United States;2. T5: Applied Mathematics and Plasma Physics, Los Alamos National Laboratory, Los Alamos, NM 87545, United States;1. Mast Cell Biology Section, Laboratory of Allergic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Md;2. Research Technologies Section, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Mont;3. Department of Laboratory Medicine, Clinical Center, National Institutes of Health, Bethesda, Md;4. Division of Allergy, Asthma & Clinical Immunology, Mayo Clinic, Scottsdale, Ariz;5. Division of Hematology/Oncology, Mayo Clinic, Scottsdale, Ariz;1. Department of Plant Physiology and Molecular Plant Biology, Institute of Biology, Faculty of Sciences, Eötvös Loránd University, Pázmány Péter sétány 1/C, Budapest, 1117, Hungary;2. Department of Agricultural Botany, Crop Physiology and Biotechnology, Institute of Crop Sciences, Faculty of Agricultural and Food Sciences and Environmental Management, University of Debrecen, Böszörményi út 138, Debrecen, 4032, Hungary;3. Department of Botany, Institute of Biology and Ecology, Faculty of Sciences and Technology, University of Debrecen, P.O. Box: 14 Debrecen, 4010 Hungary;1. Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnicka 10, Praha 6, CZ 16253 Prague, Czech Republic;2. Slovak University of Technology, Faculty of Electrical Engineering and Information Technology, Institute of Electronics and Photonics, Ilkovičova 3, 812 19 Bratislava, Slovakia;1. Ecology and Evolutionary Biology, The University of Tennessee, 569 Dabney Hall, Knoxville, TN 37996, USA;2. Florida Natural Areas Inventory, 1018 Thomasville Road, Suite 200-C, Tallahassee, FL 32303, USA |
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| Abstract: | Remote ponderosa pine (Pinus ponderosa) forests on the North Rim of Grand Canyon National Park, Arizona, USA provide valuable examples of reference conditions due to their relatively uninterrupted fire regimes, limited grazing history, and protection from logging. Wildfire is an important disturbance agent in upland forests of the Interior West, yet repeated measurements taken before and after lightning-ignited fires are rare. In 1999, a low-severity Wildland Fire Use fire burned 156 ha on Fire Point, a peninsula dominated by old-growth ponderosa pines, which had not burned for at least 76 years. We measured understory plant community and forest floor characteristics in 1998 (1 year before the fire) and 2001 (2 years after the fire) at this site and at nearby reference sites that did not burn in 1999 but have had continuing fire regimes throughout the past century. After the wildfire, the plant community at Fire Point shifted toward higher compositional similarity with the reference sites. Analysis of functional group composition indicated that this change was due primarily to an increase in annual and biennial forbs. Gayophytum diffusum, Polygonum douglasii, Chenopodium spp., Solidago spp., Elymus elymoides, Calochortus nuttallii, Hesperostipa comata, and Lotus spp. were indicative of forests influenced by recent fires. Species richness, plant cover, plant layer density and plant diversity were significantly lower at Fire Point than at the reference sites, possibly due to long-term fire exclusion, but the fire did not increase the rate of change in these variables after 2 years. Few exotic species were present at any site. Forest floor depths at Fire Point were reduced to depths similar to the reference sites, primarily due to consumption of the duff layer. There was a significant inverse relationship between the ratio of duff:litter and species richness. Compared to fire-excluded forests, old-growth ponderosa pine forests influenced by low-intensity surface fires generally have greater plant species richness (especially annual forbs) and lighter fuel loads. This study supports the continued application of the Wildland Fire Use strategy in old-growth montane forests to maintain and improve forest health by altering understory species composition and reducing fuel loads. |
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