Combining environmentally dependent and independent analyses of witness tree data in east-central Alabama

We reconstructed pre-European settlement forest composition across 13 000 km² of east-central Alabama using 43 610 witness trees recorded in the original Public Land Surveys. First, we interpolated the witness tree data to estimate broad-scale vegetation patterns. Next, we conducted species-site analysis on landforms, an approach that was dependent on underlying environmental variables yet better resolved fine-scale vegetation patterns. East-central Alabama was dominated by three community types: oak-hickory across the Piedmont physiographic province and valleys of the Ridge and Valley province, pine - blackjack oak on the Coastal Plain province and ridges of the Ridge and Valley province, and white oak - mixed mesophytic in stream valleys and floodplains. Witness tree concentration (trees/km²) was highly uniform across much of the study area. However, there was an unusually low concentration of witness trees in the southwestern corner of the study area, and an unusually high concentration in stream valleys. Another irregularity was the inability of surveyors to distinguish black oak and red oak. Overall, the interpolations provided an unbiased, yet broad-scale estimate of forest composition, while the species-landform analysis greatly increased resolution of forest cover despite the subjectivity of defining environmental variables a priori.