Forest composition: More altered by future climate change than by Euro-American settlement in western New York and Pennsylvania?

The amount of forest compositional change that occurred due to Euro-American settlement over the past two centuries is compared with changes simulated to occur in the future under 2X and 3.5X atmospheric CO ₂ scenarios. The comparison employs data from presettlement land survey records, modern forest inventory data, and future predictions from niche-based species distribution models. Comparisons are made in four independent study areas in western Pennsylvania and New York. Forest compositional changes in the recent past, attributed largely to anthropogenic factors other than climate change, are intermediate in size to changes predicted to occur as the result of climate change under the 2X CO ₂ and 3.5X CO ₂ scenarios. Results are similar across the four study areas, and are robust to variations in data collection and compilation methods. These results disagree with previous pollen-based estimates that suggested a greater relative influence of a 2X CO ₂ climate change, but do indicate that a 3.5X CO ₂ climate change may cause greater changes in forest composition than has already occurred due to anthropogenic impacts.