North American forest growth potentials reduced by climate change in the 21st century
Climate change impacts on forest growth will critically determine future ecosystem dynamics and services. It is widely recognized that when trees are subjected to a changed climate, the relationship between tree growth and climatic components (e.g. precipitation and temperature) will also change. Yet, most state-of-the-art forest growth projections handle this changing relationship only through coarse models of broadly-defined plant functional types. Using a network of over 2 million tree-ring observations spanning North America, we incorporate shifting sensitivity of tree growth to climate into continent-wide projections of changing forest growth rates for the 21stcentury.
The effect of the shifting relationship between growth and climate offsets much of the growth increase that would otherwise be projected for northern latitude biomes due to warming. Excluding non-climatic drivers of forest change, we project substantial climate-driven growth rate changes, including over 60% reductions for western and continental forests and similar magnitude growth increases for some maritime forests. Averaged across all currently forested areas in North America, we project a climate-driven decline between 6.0% and 18.4% in growth rates by the second half of the 21st century, depending upon the realized fossil-fuel emissions scenario. Our results are driven in large part by shifting climate-growth relationships at high latitudes, implying that changes in boreal climates will continue to have significant consequences on this important carbon sink. Overall, we expect a weakening ability of future forests to mitigate the negative impacts of anthropogenic carbon emissions.