Localized Native American impacts on past forest composition across a regional extent in north-eastern United States

Aim Researchers have debated impacts of past Native American land use on forests including upon tree species composition in north-eastern United States (US), with estimates of impacts ranging from local to regional extent. This study examines tree relative abundances to assess whether Native Americans influenced geographic distributions prior to Euro-American settlement. Location North-eastern United States (approx. 420,000 km(2)). Taxon Ash (Fraxinus spp.), basswood (Tilia americana), beech (Fagus grandifolia), birch (Betula spp.), cherry (Prunus spp.), chestnut (Castanea dentata), dogwood (Cornus spp.), elm (Ulmus spp.), fir (Abies balsamea), hemlock (Tsuga canadensis), hickory (Carya spp.), ironwood (Carpinus caroliniana and Ostrya virginiana), maple (Acer spp.), oak (Quercus spp.), pine (Pinus spp.), spruce (Picea spp.), tamarack (Larix laricina) and walnut (Juglans spp.), Methods We used boosted regression trees to model abundance patterns and to assess the importance of distance-based proxies of Native American land use versus environmental variables. We trained models that included and excluded distance-based proxies. Abundance estimates from original land survey records (1650-1850 CE) were acquired for taxa at 8 km spatial resolution, and related to Native American settlement locations (1500-1800 CE) and 27 environmental variables. Results When evaluated upon test data, regional-scale models of relative abundance that included distance-based proxies performed only slightly better than models that excluded them, with mean improvements in RMSE of 0.1 percentage points. Models suggest that Native American land use modestly altered the relative abundance of taxa locally, extending no more than 50 km from settlement. Models also suggest slight increases near settlement of a few percentage points in relative abundance for fire-tolerant and/or dietary taxa (e.g. oak, hickory and pine), and for early-successional taxa (e.g. ash). Main conclusions Past Native American land use had no detectable effect on forest composition across a regional extent, but increased the abundance of fire-tolerant, shade-intolerant and nut-producing trees locally.

Automated summary

This study examines the impact of Native American land use on tree species composition in the north-eastern United States before Euro-American settlement. The results suggest that Native American land use had no detectable effect on forest composition at a regional level, but locally increased the abundance of fire-tolerant, shade-intolerant, and nut-producing trees.