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Sustaining Forests

Witness Trees as Indicators of Past Fire

Research Issue

Understanding and mapping presettlement fire regimes is vitally important for ecosystem restoration, helping ensure the return of fire into ecosystems that formerly burned.  Witness trees can support this endeavor by serving as pyro-indicators of the past.  The recognition that disturbance played a key role in determining past vegetation compositions, structures, and patterns has spurred efforts to map fire regimes for restoration purposes.  The need for higher resolution maps for land management have led to an increasingly sophisticated array of maps combining soils, topography, human history, remnant vegetation, landscape concepts, and local knowledge.  This study represents a continuation of these advancements, specifically through the use of witness trees as pyro-indicators.

Our Research

[map:] Show boundaries of Pennsylvania, New Jersey, New York, Massachusetts, Connecticut, Rhode Island, Vermont, New Hampshire, and Maine.  The outlines of four national forests are also included.  The results of calculating the percentage of pyrophilic witness tree species from town-level surveys are displayed as a color gradient from red to green, with red indicating a high percentage of pyrophilic species and green a low percentage.  The red starts in the south and grades to green further north.  We classified tree species by fire relations (pyrophilic or pyrophobic) based on ecological literature and applied the classification to witness trees listed in deeds and other forms of early land surveys. From this classification, a pyrophilic percentage is calculated and these percentages spatially extrapolated via kriging to form a continuous surface across large landscapes. Current work includes portions of the central Appalachians, Lake States, and New England.

Expected Outcomes

This technique was applied to witness trees on the Monongahela National Forest, resulting in a publication (Thomas-Van Gundy and Nowacki 2013) and a set of maps to be used by the forest to help in returning fire as a disturbance regime.  The map showing percentage of pyrophilic witness tree species has also been useful in mapping ecological units and gives support to ecological site descriptions created by the NRCS. 

Similar maps were created for the Allegheny, Finger Lakes, Green Mountain, and White Mountain National Forests and, at a different scale, for the New England region.  These spatial models also will be used by fire planners and ecologists on the national forests as aides to determining where to return fire on the landscape or site scale; this work also resulted in a publication (Thomas-Van Gundy et al. 2015).

The Government Land Office bearing tree data for Minnesota was also subjected to pyrophilic/pyrophobic categorization and interpolation (Thomas-Van Gundy and Nowacki 2016).  Results from that mapping and analysis have been used by national forest staff in delimiting ecological units on the Chippewa and Superior National Forests.  This method will be applied to bearing trees for Wisconsin and combined with the Minnesota results will be used to display the vegetation tension zone line in those two states.

Research Results

Thomas-Van Gundy, Melissa A.; Nowacki, Gregory J. 2016. Landscape-fire relationships inferred from bearing trees in Minnesota. Gen. Tech. Rep. NRS-GTR-160. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 32 p.

Thomas-Van Gundy, Melissa A.; Nowacki, Gregory J.; Cogbill, Charles V. 2015. Mapping pyrophilic percentages across the northeastern United States using witness trees, with focus on four national forests. Gen. Tech. Rep. NRS-145. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 25 p.

Thomas-Van Gundy, Melissa A.; Nowacki, Gregory J. 2013. The use of witness trees as pyro-indicators for mapping past fire conditions. Forest Ecology and Management. 304: 333-344.


Research Participants

Principal Investigator

Research Partners

  • Greg Nowacki, US Forest Service Eastern Region, Regional Ecologist
  • Jason Teets, USDA Natural Resources Conservation Service, Ecological Site Description Specialist
  • Charles Cogbill, Harvard University, Ecologist

Last Modified: April 27, 2018