U.S. Department of Energy, Office of Science

Program for Ecosystem Research

Research Project   Effects of warming on tree species' recruitment in deciduous forests of the eastern United States

Principal investigator:   Jerry M. Melillo

Project goal

Determine the effects of warming on the most sensitive stage of tree species distributions (i.e., recruitment) in mixed deciduous forests in Massachusetts and North Carolina. In particular, two questions organize the research: (1) 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? and (2) Might temperate 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?

Ecosystem being studied

The eastern deciduous forest. The Massachusetts site is similar to the "Appalachian oak forest (Quercus)" vegetation type of Kuchler (1964), which is extensive in the northeast. The North Carolina site, which is in the Piedmont region, is similar to the "oak-hickory-pine forest (Quercus-Carya-Pinus)" vegetation type of Kuchler (1964), which is extensive in the southeast. The two research sites correspond to the cool (northern) and warm (southern) edges of the geographic ranges of some of the tree species to be studied.

Results

The experimental infrastructure is being developed and deployed at the research sites.

Why this is important

Climatic change has the potential to "restructure" U.S. forests during the next 50-100 years, but the details of such restructuring are uncertain. Increases in temperature, and associated changes in soil moisture, possible during the next 50-100 years could affect many aspects of tree recruitment, including germination, growth, and mortality. Unfortunately, few experimental studies have examined potential effects of climatic change on recruitment in field settings.

This research will advance scientific understanding of how the abundances and geographic distributions of several important eastern tree species near the cool and warm ends of their ranges might be affected by the amount of warming projected for the next 50-100 years by present coupled atmosphere-ocean general circulation models. 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 would therefore be of importance to society.

Methods

Air and soil warming experiments will be conducted at the Harvard Forest in central Massachusetts and at the Duke Forest in the Piedmont region of North Carolina. A set of tree species selected to represent taxa common to both sites (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) will be included in the experiments. At each site tree seeds and seedlings will be planted in common gardens established in temperature-controlled, open-top chambers (OTCs). The experimental design is replicated (n=3) and fully factorial and involves three temperature regimes (ambient, ambient + 3 degrees C, and ambient + 6 degrees C) and two light regimes (closed forest canopy [i.e., "low light"] and gap conditions [i.e., "high light"]). Measured variables will target processes indicated by previous research to be important to species success, including winter/spring responses involving temperature, and mid-summer responses to low soil moisture. Data will be assimilated for all response variables to infer integrated effects of warming on growth and survival.

Over the course of the four-year study plant community and biogeochemical attributes will be measured (in addition to measurements of soil and air temperature, relative humidity, and soil moisture in the OTCs). For seeds, germination, growth (height and diameter), dieback (seedlings frequently experience loss of the terminal stem during winter), and survival will be monitored. For seedlings, partitioning, growth, and survival will be tracked. Spring and fall phenology of the seedlings will also be measured. To help with the interpretation of the effects of the warming treatments, measurements of leaf-level photosynthesis, net nitrogen mineralization in soil, nitrogen concentration in green leaves, and biomass partitioning between aboveground and belowground plant parts will be carried out.

Personnel

Jerry M. Melillo, Marine Biological Laboratory

Jacqueline E. Mohan, Marine Biological Laboratory

James S. Clark, Duke University (subaward)

Reference

Kuchler AW (1964) Manual to Accompany the Map: Potential Natural Vegetation of the Conterminous United States. American Geological Society (Special publication No. 36), New York.

Funding period:   January 2008 to present