PARENT SESSION
Oral Session # 70: Landscape Ecology.
Presiding: S Hannon
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 201.

Modifying distance methods to estimate historical tree density from General Land Survey Records.

Sauer, Suzanne¹, Anderson, Roger^*,1, ¹ Illinois State University, Normal, Illinois, United States

ABSTRACT- Various researchers have used the Government Land Office (GLO) survey records to determine historic vegetation through the application of the distance methods to witness tree data. We test the suitability of applying modifications of the random pairs method or the quarter method to GLO records from the Shawnee National Forest Purchase Area in southern Illinois. The witness tree data was evaluated with criteria based on the distribution of the witness trees around the section or quarter section points. As a whole, the data set did not meet all criteria for either method. Data were subdivided into groups meeting specific criteria. For interior points with two witness trees, the random pair method with an exclusion angle of 202.93 degrees provided the best modification of the distance methods to convert witness tree distances to tree density. A derived correction factor of 0.74 to convert the mean witness tree distance to the square of the mean area was determined by regressing exclusion angle against correction factor. Wilcoxon sign-rank tests indicate that there are significant differences in the calculated square root of the mean based on distance method used (quarter method v. random pairs S=3665417, p<0.001; random pairs vs. the derived 0.74 correction factor S=3893716, p<0.001).

Key words: General Land Office, Shawnee National Forest, historic vegetation, distance methods