Restoring
Ecosystem Health in Ponderosa Pine Forests of the Southwest (Page 2 of
2)
Adapted from: Covington, W. Wallace, Fule, Peter Z., Moore, Margaret M., Hart, Stephen C., Kolb, Thomas E., Mast, Joy N., Sackett, Stephen S., and Wagner, Michael R. 1997. Restoring ecosystem health in ponderosa pine forests of the Southwest. Journal of Forestry 95: 23-29.
The Study Area
The study area is an unlogged stand of ponderosa pine within the Fort Valley Experimental Forest northwest of Flagstaff, Arizona, situated beneath the southern flanks of the San Francisco Peaks. The only major disturbances in the study area have been livestock grazing between 1876 and 1910 and fire exclusion since 1876. The last natural fire in the vicinity occurred in 1876. Before the United States Forest Service implemented a fire suppression policy in the area, fires occurred in the pine forests around Flagstaff at an average interval of about every two years.
Rationale for Restoration Treatments
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| Photograph courtesy of USFS Rocky Mountain Research Station, Flagstaff, AZ. |
A fundamental issue is what treatment or combination of treatments will rapidly achieve some facsimile of a healthy ponderosa pine ecosystem. The two leading candidates for ecological restoration of ponderosa pine ecosystems are prescribed burning and stand thinning.
Previous research near the study area has shown that although prescribed burning alone (without thinning or removal of forest floor fuels) could reduce surface fuel loads, stimulate nitrogen availability, and increase herbaceous productivity, it caused high mortality of presettlement trees (60% mortality of a 20-year period) and lethal soil temperatures under presettlement tree canopies. Although some thinning of postsettlement ponderosa pine trees was accomplished by prescribed burning, results were localized, unpredictable, and difficult to control. Dangerous fires can result as well as the continuing high density of postsettlement trees provides a continuous fire ladder and thus a high crown-fire potential. Research sows that prescribed burning in today's unnatural structure will not restore natural conditions in ponderosa pine-bunchgrass ecosystems. Some combination of thinning, manual fuel removal, and prescribed burning will be necessary to quickly restore these systems to more natural conditions.
Conclusions and Outlook
Preliminary results from the ecosystem restoration work are encouraging. The combination of thinning and burning- the complete restoration treatment -has changed forest structure significantly and apparently dramatically improved the health of the remaining forest. The reduction in tree competition has improved moisture availability and has likely increased insect resistance and presettlement trees. Grasses, forbs, and shrubs are responding favorably as well, indicating a shift away from a net primary productivity dominated by pine trees toward a more diverse balance across a broader variety of plants. The remaining forest now has a fire behavior fuel model 2 (Anderson, 1982), in which surface fires occur but crown fires are highly improbable, rather than a previous rating of fuel model 9, in which stand-replacing crown fires are common.
The restoration site at Fort Valley will be the focus of a long-term, interdisciplinary study. The project is to continue for the next 24 years with regular burns occurring at 3 year intervals and timed to coincide with the natural spring and summer burning season (approximately May through mid-July).
Practical ecosystem restoration treatments on a larger scale, based on research findings of the Fort Valley study, are now underway near Mt. Trumbull in the Arizona Strip country north of the Grand Canyon. More practical approaches are being utilized recognizing that regional restoration treatments thousands of acres in size cannot undergo some of the treatments done on a much smaller scale. For instance, raking of the forest floor away from presettlement trees is being done rather than removing it completely, a much more labor intensive process. Because the Mt. Trumbull area is larger, some variables which operate on a larger scale are more easily measured, such as passerine bird populations, community structure of insects, particularly butterflies, and other indicators of landscape-scale ecosystem health.