Mixedwood forests must be managed as a multiuser renewable resource, as an integral component in a landscape, and on a sustained basis. Large-scale spatial data are crucial for this approach. We describe a comprehensive spatial data base assembled by the Forest Landscape Ecology Program, which is suited for managing boreal mixedwood forests of Ontario. Forest land cover, historical forest harvests, historical forest fires, surficial geology and substrate, topography, and climate are basic components of the data base. These data permit the use of new tools such as geographic information systems for increased spatial accuracy in decision making. They also present an opportunity for forest managers to link the multiscale facets of forestry practice explicitly: policy development, strategic planning, and silvicultural operations.