Using witness trees as pyro-indicators to depict past fire environments across the eastern United States

Understanding past fire environments is vitally important for applying silvicultural treatments, which often include prescribed burning to restore fire-dependent ecosystems. We have developed a novel method by which witness trees can be used as pyro-indicators to map past fire environments. The stepwise process first involves partitioning witness trees into two classes, pyrophobic and pyrophilic, based on their known ecophysiological traits. Pyrophilic percentages are then calculated at survey corners by dividing the number of pyrophilic trees by the total number of trees. Next, statistical spatial interpolation is applied to this point-based data set to produce a continuous response surface of pyrophilic percentages. The resultant maps capture gradients of fire importance across the pre-European-settlement landscape, which can be coupled with historic fire regime maps, thus providing additional information for better understanding and explaining past fire environments. We have applied this technique to various available witness-tree databases across the eastern United States. This paper serves as a compendium of our collective work to date.