The recognition that disturbance played a key role in determining past forest composition, structure, and patterns has spurred efforts to map fire regimes for ecosystem restoration. Forest Service scientists at the agency’s Northern Research Station classified tree species by their relationship to fire (pyrophilic or fire-adapted and pyrophobic, not fire-adapted) and applied the classification to witness trees listed in deeds and other forms of early land surveys. From this classification, a pyrophilic percentage was calculated and these percentages spatially extrapolated to form a continuous cover across large landscapes. This technique was applied to witness trees on the Monongahela National Forest, resulting in a set of maps that can be used to help return fire as a disturbance regime. Similar maps were created for the Allegheny, Finger Lakes, Green Mountain, and White Mountain national forests, the New England region, and for Minnesota. The distribution of pyrophilic witness trees has also been useful in mapping ecological units and gives support to ecological site descriptions created by the U.S. Department of Agriculture Natural Resources Conservation Service. The pyrophilic percentage is being used in Minnesota and Wisconsin to explore drivers of the regionally important tension zone line between vegetation biomes and to create an alternate version of that line.