Modifying and coupling a simple growth model (ALMANAC) with a watershed-scale model (SWAT) to evaluate harvest impacts on streamflow on the Boreal Plain.
MacDonald, Douglas*,1, Kiniry, Jim2, Arnold, Jeff2, Putz, Gordon3, Russell, Jonathan4, Prepas, Ellie1, 1 Lakehead University, Thunder Bay, Ontario, Canada2 United States Department of Agriculture, Temple, Texas, USA3 University of Saskatchewan, Saskatoon, Saskatchewan, Canada4 Millar Western Forest Products Ltd., Edmonton, Alberta, Canada
ABSTRACT- Deterministic hydrological models that function on a watershed scale may be valuable tools in the development of Detailed Forest Management Plans (DFMPs) by providing estimates of the impacts of different harvest patterns to streamflow and water quality. As a part of the FORWARD research initiative, the quantity and quality of stream water in 16 watersheds ranging from 200 to 25000 ha and predominantly located in the Millar Western Forest Products Forest Management Area near Whitecourt AB, have been monitored on a daily time-step since 2001. Portions of some of these watersheds were harvested during winter 2003-2004. Monitoring data were used to evaluate, validate and modify a deterministic watershed scale hydrological model. The Soil and Water Assessment Tool (SWAT), developed by the U.S. Department of Agriculture, was adapted to boreal forest conditions and streamflow modelled in a 1600 ha undisturbed watershed in the FORWARD study area. To allow the SWAT model to estimate the impacts of harvest on streamflow, it has been coupled with a simple multi-species physiological plant growth model (ALMANAC) to estimate the competition between herbaceous and woody species with crop species during the regeneration of cutblocks and the impact of silvicultural activities, such as herbicide application and thinning, on streamflow. The modified ALMANAC model provides good estimates of variations in biomass production associated with differences in ecosite classification and site indices by crop species (trembling aspen, white spruce, black spruce and lodgepole pine) observed in Millar Western's temporary sample plot survey data. The model also reproduced variations with site index in the empirical height age relationships for juvenile crop species in competition with grass, forbs and shrubs developed from Millar Western's regeneration survey data. SWAT-ALMANAC provided good estimates of base- and storm-flow and reasonable estimates of spring snowmelt. The ability of the model to estimate the impacts of the 2003-2004 harvest on runoff from the FORWARD watersheds will be evaluated. Model projections of impacts of harvest patterns will be used to define limits on harvest area in watersheds as part of the Millar Western DFMP process.
Key words: modeling, ALMANAC, SWAT, competition
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