Sara CoffeyScience Collaberative Research ProgramWillamette UniversityEnvironmental and Earth SciencesSummer 1999
Before European settlement the Willamette Valley is believed to be an area dominated by grasslands and oak savanna. The land soon began to change once Europeans settled upon it. The large influx of European settlement occurred in the 1840s. Europeans indirectly influenced the fire regime by reducing Native American populations, which reduced the frequency of ignitions by Native Americans. Fire suppression began in 1910 (Wallin 1996). There was a substantial reduction in the area of natural vegetation since European settlement because much of the land base has been usurped for buildings, agriculture, or intensive, short-rotation industrial forestry (Wallin 1996). With out burning, Oregon White Oak (Quercus garryana) and tall grass stands were gradually replaced by the better adapted Douglas fir (Pseudotsuga menziesii) bigleaf maple (Acer maerophyllum) and grand fir (Abies grandis) woodlands removing the tall grass prairies dominate presence in the valley (Kimmerling and Jackson, 1985:61 as cited from Kenneth Duncan 1999).
At Bonesteele Park in Marion County, Oregon, land managers are interested in encouraging an open oak savanna type edge between restored prairie and upland forest. Other restoration projects have shown that prescribed fire is a useful management tool for restoring vegetation. In order to implement prescribed burning, one must characterize the fuels, since they drive fire. These characteristics include fuel load and seasonality of fuels. Accurate measurements of surface fuel loadings and consumption during prescribed fires is important for understanding the effects of fire on vegetation (Finney 1993).
In this study I will focus on the fuel load in the forested area. The main question that I intend to answer is: Are fuel conditions such that prescribed fire can be used along the prairie/forest ecotone? I answer this question by measuring the fuel load differences between the edge and the interior of the forest. The purpose of examining the fuel load is to help land managers practice fuel management and plan for prescribed fire (Brown 1974). The identification of fuels can give landowners an opportunity to plan and understand the potential effect on vegetation of certain fuel levels. It also allows managers to plan ways to reduce the hazardous effects that may result if wild fire occurs.
In order to determine if the fuel conditions at Bonesteele Park are such that prescribed fire can be used along the prairie/forest ecotone I will test for significant differences among fuel loads, along a transect from prairie to interior. I hypothesize that the fuel load will increase from the edge of the forest throughout the gradient into the interior because of the finer fuels at the edge and the larger fuels in the interior.
The soils at Bonesteele Park are Nekia silty clay loam (Marion County Soil Survey 1972 as cited in Ridgeline Resource Planning). The site has a slope between 5-20% as determined from the U.S.G.S. topographic mapping. Bonesteele slopes form north to south with an overall southern exposure. Annual precipitation is measured in nearby Salem (39.24 in/yr) and Stayton (51.48 in/yr) (Taylor & Bartlett 1993 as cited in Ridgeline Resource Planning.
Pairwise comparisons between the five plot types were run using the Mann-Whitney test on the fuel categories where significant differences existed (Table 2). Litter load differed significantly between the prairie and the edge plots (p=0.0265), the prairie and interior plots (p=0.0211), and the prairie and the deep interior (p=0.0265).
One hour fuel loads differed significantly between the prairie and the transition (p=0.0265); between the prairie and the interior (p=0.0265); between the prairie and the deep interior (p=0.0265); and between the middle edge and the deep interior plots (p=0.0304).
Ten hour fuel loads differed significantly between the prairie and the transition (p=0.0265); between the prairie and the interior (p=0.0265); between the prairie and the deep interior (p=0.0265).
Total fuel loads differed significantly between the prairie and the edge (p=0.0265); between the prairie and the transition (p=0.0265); between the prairie and the interior (p=0.0265); and between the prairie and deep interior (p=0.0265).
Total fuel loads range from 1.65 to 7.25 tons/ha.
Fuels at Bonesteele Park forest can be categorized in the fuel model 9, which is based on the type and amount of fuel present. Fuel model 9 is a mixed hardwood coniferous forest. Knowing the fuel model enables land managers to predict fire behavior and to rate fire danger. Based on these results, the low fuel loads and fuel model 9 characterization indicate that the best conditions for prescribed burning most likely occur in the early fall while it is still dry, but after leaf fall has occurred. Summer burning would not be advisable due to patchy, low fuel loads.
Agee, James. 1993. Fire Ecology of Pacific Northwest Forests. Washington D.C.: Island Press.
Brown, James. 1974. Handbook for Inventorying Downed Woody Material. USDA Forest Service.
Finney, M.A. 1993. Fuel loading, bulk density, and depth of forest floor in coast redwood stands. Forest Science 39:617-622.
Ridgeline Resource Planning. 1999. Bonesteele Park Upland Prairie Restoration. [Online] Available: http;//www.org/mcpark/restore.html.
Wallin, D.O., Swanson, I.J., Marks, B., Cissel, J.H., and J. Kerlis. 1996. Comparison of managed and pre-settlement landscape dynamics in forests of the Pacific Northwest, U.S.A. Forest Ecology and Management 85: 291-309.