The Grand Fir Mosaic Ecosystem -- History and Management Impacts

Abstract

The Grand Fir Mosaic (GFM) ecosystem is found on ash-cap soils in some mid-elevation forests of northern Idaho and northeastern Oregon. Harvesting on GFM sites results in successional plant communities that are dominated by bracken fern (Pteridium aquilinum) and western coneflower (Rudbeckia occidentalis), and have large populations of pocket gophers (Thomomys talpoides). Succession to trees and shrubs is very slow on disturbed GFM sites. Four factors contribute to the protracted stages of bracken fern plant communities and the slow rate of succession to woody plants: (1) competition among plants for site resources, (2) allelopathy from bracken fern and western coneflower, (3) pocket gopher activity, and (4) a nonallophanic soil forming process. Nonallophanic soils occur under the bracken fern successional plant communities -- they are dominated by Al-humus complexes, have strongly acid pH, have high KCl-extractable Al, and may cause Al toxicity to plants. Allophanic soils occur under forested conditions -- they are dominated by allophane and imogolite, have weakly to moderately acid pH, and have low Al availability. Allophanic and nonallophanic soils exist side-byside in the GFM, with mineralogy being dependent upon the dominant vegetation. Bracken fern and western coneflower, with below-ground carbon inputs from their well-developed root systems, provide a mechanism that promotes the shift from allophanic to nonallophanic soils. Recommendations for reforesting GFM sites are provided.

Parent Publication

• Volcanic-ash-derived forest soils of the inland Northwest: Properties and implications for management and restoration

Citation

Ferguson, D. E.; Johnson-Maynard, J. L.; McDaniel, P. A. 2007. The Grand Fir Mosaic Ecosystem -- History and Management Impacts. In: Page-Dumroese, Deborah; Miller, Richard; Mital, Jim; McDaniel, Paul; Miller, Dan, tech. eds. 2007. Volcanic-Ash-Derived Forest Soils of the Inland Northwest: Properties and Implications for Management and Restoration. 9-10 November 2005; Coeur d’Alene, ID. Proceedings RMRS-P-44; Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. p. 175-184