Photo Credit

USDA Forest Service photo by Jenna Zukswert.

Forest canopy at Bartlett Experimental Forest.

Forests in New England are important for wood production and carbon sequestration. Both ecosystem services depend on carbon cycling, and so it is important for land managers to understand carbon cycling trends in a changing climate. As carbon dioxide concentrations increase, photosynthesis is also expected to increase. While we might expect this increase in photosynthesis to increase wood production and carbon sequestration, recent data from the Bartlett Experimental Forest in New Hampshire shows that the opposite may be true; wood production and carbon sequestration rates have decreased over time.

In addition to stand age effects, one reason for this decrease may relate to the role of nitrogen in plant growth and production. Nitrogen is an important component of chlorophyll, proteins, and other molecules that constitute trees, and so trees need nitrogen to grow. If carbon dioxide increases, but nitrogen availability does not or decreases, then the amount of nitrogen available in the forest limits tree growth.  

This study aims to determine whether decreases in wood production and carbon sequestration with increasing carbon dioxide concentration are common throughout New England and can be explained by changes in nitrogen availability. Measurements made at the Bartlett Experimental Forest and Howland Research Forest and in regionwide analyses will clarify the mechanisms behind the patterns observed in carbon cycling in New England forests and improve forest simulation models that predict forest growth in the future.

Approach

This research will determine whether rising carbon dioxide concentrations have led to increases in photosynthesis and decreases in wood production and carbon sequestration across New England, and whether a change in nitrogen availability might explain decreasing wood production and carbon sequestration. This study will be conducted in forests that represent two of the major forest types in New England: northern hardwood (Bartlett Experimental Forest, New Hampshire) and boreal conifer (Howland Research Forest, Maine).

Photo Credit

USDA Forest Service photo.

Eddy flux tower at Bartlett Experimental Forest.

Researchers will revisit sets of monitoring plots in both sites that were established decades earlier and measure wood production as well as soil and leaf nitrogen. They will also measure carbon and nitrogen pools and fluxes around the base of eddy covariance towers, which measure carbon fluxes in the atmosphere, to get a better sense of how carbon is allocated throughout the ecosystem. Researchers will also use Forest Inventory and Analysis data with data from Bartlett Experimental Forest and Howland Research Forest to observe how widespread the trend of decreasing carbon sequestration and wood storage is in New England.  

With this new information, the researchers plan to improve existing forest simulation models by incorporating more accurate relationships among carbon dioxide, nitrogen availability, and carbon allocation. These improved models will produce more accurate projections of future forest growth, which will aid forest management.

Expected Outcomes

• Reveal relationships among carbon dynamics and nitrogen availability.
• Analyze regional trends in carbon sequestration and wood production.  
• Improve forest simulation models to predict forest growth in a changing climate.