Climate change is restructuring forests of the United States, although the details of this restructuring are currently uncertain. Rising temperatures of 2 to 8°C and associated changes in soil moisture will shift the competitive balance between species that compete for light and water, changing the abilities to produce seed, germinate, grow, and survive. We are using large scale experiments to determine the effects of warming on the most sensitive stage of species distributions, i.e., recruitment, in mixed deciduous forests in southern New England and in the Piedmont region of North Carolina.
Two questions organize our research:
- Might temperate tree species near the “warm” end of their range in the eastern United States decline in abundance during the coming century due to projected warming?
- Might trees near the “cool” end of their range in the eastern United States increase in abundance, or extend their range, during the coming 100 years because of projected warming?
To explore these questions, we are exposing seedlings to air and soil warming experiments in two eastern deciduous forest sites; one at the Harvard Forest in central Massachusetts, and the other at the Duke Forest in the Piedmont region of North Carolina. We focus on tree species common to both Harvard and Duke Forests (such as red, black, and white oaks), those near northern range limits (black oak, flowering dogwood, tulip poplar), and those near southern range limits (yellow birch, sugar maple, Virginia pine). At each site, we plant seeds and seedlings of in common gardens established in temperature-controlled, open-top chambers. The experimental design is replicated and fully factorial and involves three temperature regimes (ambient, +3°C and +5°C) and two light regimes (closed forest canopy (low light) and gap conditions (high light)). Measured variables include winter/spring responses to temperature and mid-summer responses to low soil moisture.
This research will advance our understanding of how the abundances and geographic distributions of several important eastern tree species near the cool and warm ends of their ranges will change during the century because of projected warming. Warming-induced changes in eastern tree abundances and distributions have the potential to affect both the quality and quantity of goods and services provided by eastern forests, and will therefore be of importance to society.
- Jerry Melillo, Marine Biological Laboratory, Woods Hole, MA.
- Jacqueline Mohan, Odum School of Ecology, University of Georgia, Athens, GA.
- Jim Clark, Nicholas School of the Environment, Duke University, Durham, NC.
Former Students: Carl Salk
Funding: United States Department of Energy
- Clark, J.S., J. Melillo, J. Mohan, and C. Salk. 2013. The seasonal timing of warming that controls onset of the growing season. Global Change Biology, in press.