Modeling the Ecohydrologic Response of the Forest-Grassland Ecotone in Western Canada to Changes in Annual Precipitation

The ecotone between the southern boreal forest and the grassland of western Canada is controlled by the water balance, and is therefore sensitive to climate change. Although ecohydrologic fluxes are being investigated at the Boreal Ecosystem Research and Monitoring Sites (BERMS) at the stand level, the ecohydrologic response of this ecotone to climate change is poorly understood. We use CTEM (the Canadian Terrestrial Ecosystem Model), coupled to CLASS (the Canadian Land Surface Scheme), to explore the structural and functional responses of the forest-grassland ecotone to climatic variability. The initial evaluations of CLASS-CTEM are being done using data from three mature forest sites (jack pine, aspen and black spruce) at BERMS and one grassland site. The model is forced with observed climate data between 1997 and 2010 by using each year, run repeatedly with a 400 year spin up, as one climatic scenario. Preliminary results show a sigmoidal response of annual gross primary production (GPP) to annual precipitation within each plant functional type, with limited GPP at low precipitation, higher but uniform GPP at high precipitation, and an intermediate precipitation range where GPP responds sensitively to increasing precipitation.