Divergent historical and current forest composition in Kentucky, including Daniel Boone National Forest, United States

Outcomes of European colonization encompass surface fire exclusion followed by the forestation of open ecosystems and tree densification within forests, with concomitant replacement of fire-tolerant tree species, specifically oaks, by fire-sensitive tree species. In Kentucky, a 10.5 million ha area of the eastern United States, I compared tree composition between a historical assessment (1907–1909) and modern surveys (2010–2014), utilizing a divergence metric of squared-chord distance, which revealed a similar progression. Following the time since Euro-American settlement and associated fire exclusion, historically dominant fire-tolerant oaks decreased from 52% of all trees to 21% of all trees in Kentucky, while maples increased from 5 to 19% of all trees, reflecting shared changes across three regions. The Loess Hills region in western Kentucky and the Central Interior, a flat region of historical grasslands, displayed greater tree composition divergence than the Appalachian Mountain region in eastern Kentucky. The least decrease in oaks, at 19 percentage points, and the greatest decrease in fire-tolerant shortleaf pine ( Pinus echinata ), at 5.5 percentage points, occurred in the Daniel Boone National Forest, within the Appalachian region. American chestnut ( Castanea dentata ) decreased by nine percentage points in the Appalachian region, where red maple ( Acer rubrum ), previously of trace abundance, became the most abundant tree species at 14% of all trees, with yellow-poplar ( Liriodendron tulipifera ) at 12% of all trees. American beech ( Fagus grandifolia ) decreased by nine percentage points in the Interior region, where eastern redcedar ( Juniperus virginiana ), also previously of trace abundance, became the most abundant tree species at 12% of all trees. Sweetgum ( Liquidambar styraciflua ) decreased in the Loess region, where green ash ( Fraxinus pennsylvanica ) became the most abundant species, along with a new addition of planted loblolly pine ( Pinus taeda ). Kentucky contains a range of ecosystems, reflecting trends common to the eastern U.S. of decreased fire-tolerant species relative to fire-sensitive species following fire exclusion, as well as trends specific to regions, depending on species distributions.