Cary Institute of Ecosystem Studies
Millbrook, NY 12545
|Mary A. Arthur
Department of Forestry
University of Kentucky
Lexington, KY 40546
BEECH BARK DISEASE (BBD) is an introduced disease of American beech that has had severe effects on the structure of the beech population throughout the Northeastern U.S. The disease was first imported into North America from Europe around 1890, and was first reported in the forest at Hubbard Brook in the 1970s. Caused by the interaction of a scale insect and a bark-cankering fungus, the disease typically kills trees slowly over the course of 10 years or more.
Our research focused on determining what species replace beech trees when they die, and how the change in tree species affects the soil. This project compared the forest in the White Mountains, including Hubbard Brook, with the Catskill Mountains in New York State, which have a similar forest type.
Our sampling centered around places in the forest where we could ascertain that a canopy beech tree had formerly stood, using a stump and/or downed log as evidence of its presence and size. We chose former beech plots for which the canopy had "closed" with other trees that had filled in the gap left by the dead beech. In this former gap, we measured which trees were present and the chemistry of the soil underneath them.
We found that in soils of higher exchangeable calcium concentration, these former beech gaps were more likely to be filled by sugar maple, while on lower-calcium sites there was a greater tendency for younger beech to replace the dead canopy dominant. These younger beech, which may be either from seeds or sprouting, will likely get the disease themselves and die younger than they might have without the disease. We also found that greater abundance of sugar maple led to lower forest floor mass, lower carbon-nitrogen ratio, and greater nitrate concentration in the soil. These patterns were generally stronger in the Catskill forests than in the White Mountains, but were present in both locations.
|Figure 2: Measuring the vegetation in a plot formerly occupied by a beech tree.|
These results suggest that the geological characteristics of a site, which largely control the calcium availability, have a significant influence on how the forest responds to this introduced disease. In higher-calcium sites, the BBD sends the forest on a trajectory of increased maple dominance, while on lower calcium sites beech often replaces itself and remains dominant, though as a smaller, and often deformed, tree. The change in species from beech to maple has an impact on the carbon and nitrogen cycling in the forest, and the production of more nitrate in the soil in maple dominated stands likely will lead to greater nitrogen leaching into streams and lakes.
This research was supported by the USDA (Northeastern States Research Cooperative), the National Science Foundation, and the Hubbard Brook LTER.
Date Prepared: June 2013