Reconstructing structural indices of elm prior to the spread of Dutch elm disease in the forests of Indiana

Dutch elm disease (DED) spread throughout the United States in the 20th century and resulted in mortality of many elm trees. In this study, bearing trees from Indiana’s historical Public Land Survey (PLS) records were used to reconstruct species mingling, diameter differentiation, and competition indices of elm prior to the introduction of DED. Prior to DED spread, elm had an average species mingling index of 0.77, a diameter differentiation index of 0.36, and a competition index of 1.22. Forests where elm had significantly lower mingling indices occurred along rivers. Forests where elm had significantly lower diameter differentiation indices were located near the homeland of the Piankashaw Tribe, which later became the French settlement of Vincennes. Forests where elm had significantly higher diameter differentiation indices were in areas that experienced later settlement by Europeans. Competition indices for elm were regularly dispersed across the state with no significant spatial clustering. This study demonstrated the impact of physiography and human activities on the structure of elm prior to the spread of DED and documented the successful application of PLS records to provide an ecological baseline of elm prior to the introduction of a non-native pathogen.