Projecting the distribution of forests in New England in response to climate change

Aim To project the distribution of three major forest types in the northeastern USA in response to expected climate change. Location The New England region of the United States. Methods We modelled the potential distribution of boreal conifer, northern deciduous hardwood and mixed oak-hickory forests using the process-based BIOME4 vegetation model parameterized for regional forests under historic and projected future climate conditions. Projections of future climate were derived from three general circulation models forced by three global warming scenarios that span the range of likely anthropogenic greenhouse gas emissions. Results Annual temperature in New England is projected to increase by 2.2-3.3 degrees C by 2041-70 and by 3.0-5.2 degrees C by 2071-99 with corresponding increases in precipitation of 4.7-9.5% and 6.4-11.4%, respectively. We project that regional warming will result in the loss of 71-100% of boreal conifer forest in New England by the late 21st century. The range of mixed oak-hickory forests will shift northward by 1.0-2.1 latitudinal degrees (c. 100-200 km) and will increase in area by 149-431% by the end of the 21st century. Northern deciduous hardwoods are expected to decrease in area by 26% and move upslope by 76 m on average. The upslope movement of the northern deciduous hardwoods and the increase in oak-hickory forests coincide with an approximate 556 m upslope retreat of the boreal conifer forest by 2071-99. In our simulations, rising atmospheric CO2 concentrations reduce the losses of boreal conifer forest in New England from expected losses based on climatic change alone. Main conclusion Projected climate warming in the 21st century is likely to cause the extensive loss of boreal conifer forests, reduce the extent of northern hardwood deciduous forests, and result in large increases of mixed oak-hickory forest in New England.