Harvard Forest LTER Site

The organizing theme of the Harvard Forest LTER (see photo, bottom of page 4) is a comparison of the effects of several important kinds of natural and anthropogenic disturbances on the structure and function of forested ecosystems. A major goal is to determine if recent anthropogenic chemical inputs cause fluctuations in ecosystem structure and function that are beyond the ranges prod uced by natural disturbances. A second major goal is to determine if there is a significant interaction between natural disturbances and chronic chemical deposition that could not be predicted from system responses to each factor independently.

The disturbance processes we will investigate include:

1. Catastrophic windthrow due to broad-scale hurricanes
2. Canopy gaps due to the small-scale blow- downs of isolated individuals or groups of overstory trees
3. Selective loss of tree species due to pathogens, resulting in standing dead overstory trees
4. Chronic nitrogen and sulfur inputs through atmospheric deposition
5. Soil neutralization. Four related research components will provide additional information with which to interpret ecosystem responses.

These include:

1. Addition or removal of litter on the forest floor, and its effects on blogeochemical cycling
2. The role of coarse woody debris in biogeochemical cycling
3. The movement of animals and birds in relation to forest patches, and the effects of large mammal (deer) herbivory
4. The role that developmental and architectural constraints play in determining plant responses to disturbance

Historically, the primary forms of disturbance at the Harvard Forest have been physical disruption by catastrophic (hurricane) and small-scale windthrow and the recent (chestnut, elm and beech) and mid-Holocene (hemlock) decline of major tree species due to pathogens. The size of disturbed areas has ranged from small canopy gaps to the destruction of whole stands by hurricanes. In order to provide a comprehensive historical context for interpreting our proposed experimental treatments, we plan to integrate the extensive historical records of the Harvard Forest with new research results in forest dynamics throughout the Holocene.

Recent and future changes in the chemical loading experienced by central New England forests due to atmospheric deposition can be expected to alter rates of internal processes such as primary production and nutrient cycling affect organism ecophysiology and interactions differentially, and may have profound effects on atmosphere-biosphere interactions through changes in trace gas fluxes. The hypothesis that chronic chemical disturbances, and/or their interactions with natural windthrow disturbance, cause greater variation in forest function than natural disturbance alone will be subjected to vigorous examination to determine whether the rates of function in the treated stands lie outside the range of values measured through the successional sequence following windthrow.

Specific research areas to be pursued include:

• Physiological ecology of major tree species in conjunction with micrometeorological monitoring and demographic studies (Bazzaz)
• Plant development and plant architectural response (Tomlinson)
• Historical studies of vegetation change and disturbance processes (Patterson, Foster)
• Soil microbiology (Torrey, Linkins, McClaugherty)
• Biosphere-atmosphere interactions (Wofsy, Steudler)
• Organic matter dynamics (Aber, Nadelhoffer)
• Element cycling (Melillo, Aber, Steudler)
• Landscape-level processes (Foster, Forman)

Research will employ specific tools such as

• Remote sensing (Aber, Melillo)
• Geographic Information System (Tomlin)
• Stable isotopes (Nadelhoffer)
• Ecosystem and atmospheric modeling (Aber, McElroy)
• Micrometeorological techniques (Bazzaz)
• Trace-gas measurement (Steudler, Wofsy)

For additional information contact David R. Foster, Harvard Forest, Harvard University, Petersham, MA 01366.