Fuel Load - The dry weight of combustible materials per unit area. Recommended SI units are kilograms per square metre (kg/m2) and tonnes per hectare (t/ha) (1.0 kg/m2 is equivalent to 10 t/ha).
(CIFFC Glossary of Forest Fire Management Terms)
Measuring Fuel Load
Several wildland fuel load measurement methodologies are available for fire behaviour research and it is important that researchers are aware of the strengths and weakness of each methodology in order to implement an accurate and efficient fuel-sampling program. (Sikkink and Keane, 2008,p.363)
While destructive sampling is the most accurate method for determining grass fuel loading, it is labor intensive and time consuming to collect and weigh samples. Other more practical indirect tools are available which will be quicker and easier to use for grass fuel loading estimation. (Kidnie 2009) This paper discusses and tests three simple and indirect methods for estimation of grass fuel loading in the southern Ontario tallgrass prairie fuel type and provides statistical relationships between fuel loads and instrument readings.
Grass disc meter
Baxter (2006) tested a disc meter (Trollope and Potgiester 1986) to compare resultant grass load measurements with load measurments from traditional clip and weigh methodology. The disc meter is a pole with an alumimun disc that slides up and down on the pole. In this study, the disc was allowed to slide down the pole until supported by the grass. The height on the pole was recorded and the grass under the disc was clipped and oven dried. The height on the pole was compared to the fuel load (oven dry weight) to determine the strength of the statistical relationship.
Destructive sampling techiques in grass fuel types involves the clipping, collection, and storage of the entire mass of grass stems within a square (usually 30cm. X 30 cm.) or a circle. In the case of the disc meter testing research (Baxter 2006) the grass area to be clipped under the disc (1662 cm2) was defined by a circular border with the same diameter as the disc. The oven dried grass is weighed (grams) and a fuel loading is calculated (kilograms per square meter can be converted to tonnes per hectare).(p.2)
Field Reference Photo Guide
The photo series method is the most common visual fuel loading assessemnt tool. Distinct fuel environments are photographed using an oblique view and inventoried to provide a numerical value for the fuel loading of each sample site. Fuel loading in areas under study can be estimated by visually comparing the study area with photos in the series. (Sikkink and Keane, 2008,p.363) (Baxter 2009) developed a field reference photo guide for Central and Northern Alberta that allows users to estimate grass loading for an area of interest by comparing a visual observation of the area against photographs of sample plots with known fuel loading. This study used the grass disc meter (Trollope and Potgiester (1986) and traditional oven dry methods to determine fuel loading in sample plots of varying fuel loading. TheTallgrass Prairie Fuel Load Photo Series (Kidnie 2009) provides photos which can be used as a quick fuel loading estimation or when other fuel loading tools are not available.
Forest Fuel Loading
The fuel loading measuring methodology chosen will be determined by the project scope, the fuel type under study and the uniform distribution of the fuels across the area under study. A fuel loading sampling for a uniform distribution of litter layer across the area under study may only require destructive sampling of a representative sample site. However, when the entire fuel complex is under study, more complex and intensive sampling techniques such as line transects and over study sampling will be required.
Field Reference Photo Guide
Lavoie et al. 2010 have developed a Photo Guide for Quantitatively Assessing the Characteristics of Forest Fuels in a Jack Pine – Black Spruce Chronosequence in the Northwest Territorieswhich allows users to assess fuel loads and other fuel characteristics at different stand ages following a crown fire.
Destructive Sampling Method
Gibos (2010) studied a specific component (litter layer) of a lodgepole pine fuel environment and the effect of slope and aspect on fine fuel moisture content implementing a descructive sampling methodology as one of the research tools. A 30 cm. square was placed on the ground in a sample site representative of area under study and the requisite fuels inside the square were collected separately and placed in storage containers for drying. (p.132)
During the International Crown Fraction Modelling Experiment, destructive sampling in the organic layer was conducted in more than 100 sample plots (30 X 30cm) adjacent to the actual burn plots. (Alexander et al. 2004,p. 9) Sampling in these representative areas outside the burn plots reduced the disturbance and trampling of forest fuels in the area under study. Using the 30 X 30 cm. sampling frame the full depth of the organic layer was measured at the midpoint of each side of the frame. The organic layer was then sectioned into 2-cm depth classes and individual fuel layers were bagged and oven dried. Inorganics were separated from the dried samples to determine the amount of fuel available in each section of the organic layer.
Line Intersect Method
The line intersect method provides a methodology for estimating the forest fuel loading in sample plots representative of a forested areas or slash fuels. This methodology is described by Van Wagner (1982)as 'a vertical plane extending as high above the ground as necessary to include all material in direct or indirect contact with the ground.'(pg. 9) Each intersection between the sample line and wood piece is tallied according to accepted size classes with the final summation of each size class converted to fuel volume and fuel weight. Total fuel volume of the sample plot is achieved by totalling the volume for each size class.
A slash fuel sampling methodology utilizing the line intersect method is described in the Canadian Forest Service publication, Measurement and Description of Fuels and Fire Behaviour on Prescribed Burns: A Handbook (page 5).
Alexander et al.(2004) provide a detailed description for using the line intersect method to inventory dead down surface fuels in the experimental plots under study in the International Crown Fraction Modelling Experiment.(page 9)
Alberta Fire and Vegetation Monitoring Program
Alexander, M.E.; Stocks. B.J.; Lawson, B.D. 1991. Fire behavior in black sprucelichen woodland: the Porter Lake project. For. Can., Northwest Reg., North. For. Cent., Edmonton, Alberta. Inf. Rep. NOR-X-310.
Alexander, M.E.; Stefner, C.N.; Mason, J.A.; Stocks, B.J.; Hartley, G.R.; Maffey, M.E.; Wotton, B.M.; Taylor, S.W.; Lavoie, N.; Dalrymple, G.N. Characterizing the Jack Pine - Black Spruce Fuel Complex of the International Crown Fire Modelling Experiment (ICFME). INFORMATION REPORT NOR-X-393 Canadian Forest Service Northern Forestry Centre 2004
Gibos, Kelsy 2010. Master of Science in Forestry, University of Toronto. Effect of Slope and Aspect on Litter Layer Moisture Content of Lodgepole Pine Stands in the Eastern Slopes of the Rocky Mountains of Alberta.
Hély C. Bergeron Y. and Flannigan M.D.. Coarse woody debris in the southeastern Canadian boreal forest: composition and load variations in relation to stand replacement. Can. J. For. Res. 30: 674–687 (2000)
Kidnie,S.M. 2009. Fuel Load and Fire Behaviour in the Southern Ontario Tallgrass Prairie. Masters of Science in Forestry 2009. Graduate Department of Forestry, University of Toronto.
Lavoie, N.; Alexander, M.E.; Macdonald, S.E. 2010. Photo guide for quantitatively assessing the characteristics of forest fuels in a jack pine – black spruce chronosequence in the Northwest Territories. Nat. Resour. Can., Can. For. Serv., North. For. Cent., Edmonton, AB. Inf. Rep. NOR-X-419.
Lutes, Duncan C.; Keane, Robert E.; Caratti, John F.; Key, Carl H.; Benson, Nathan C.; Sutherland, Steve; Gangi, Larry J. 2006. FIREMON: Fire effects monitoring and inventory system. Gen. Tech. Rep. RMRS-GTR-164-CD. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station.
McRae,D.J.; Alexander,M.E.; and Stocks,B.J. 1979. Measurement and description of fuels and fire behavior on prescribed burns: A handbook. Can. For. Serv. Rep. O-X-287, Great Lakes For. Res. Cent., 56 pp.
Nalder, I.A., Wein, R.W., Alexander, M.E., de Groot, W.J. 1999. Physical Properties of Dead and Downed Round-wood Fuels in the Boreal Forests of Western and Northern Canada. International Journal of Wildland Fire. 9(2):85-99.
Trollope, W.S.W.; Potgieter, A.L.F. 1986. Estimating grass fuel loads with a disc pasture meter in the Kruger National Park. Journal of the Grassland Society of South Africa 3(4):148–152.
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