The Hubbard Brook Experimental Forest (43°56'North, 71°45'West; the geographic center of the HBEF) is a 3,138-hectare bowl-shaped valley with hilly terrain, ranging from 222 to 1,015 m altitude, located in the White Mountain National Forest, near North Woodstock, New Hampshire. The forest, established in 1955 by the U.S. Forest Service as a hydrological research site, is home to the Hubbard Brook Ecosystem Study (HBES). The HBES was established by a cooperative agreement in 1963. In 1988 the HBEF was designated as a Long Term Ecological Research (LTER) site by the National Science Foundation. The HBEF was originally designated as a site for the research of flood flows, water quality, and water supply among other water issues facing the New England region at the time.
The Hubbard Brook flows through New Hampshire's White Mountain National Forest and drains a range of small mountains. The tributaries of Hubbard Brook form a set of discrete watersheds, separated by mountain ridges. Six of the south-facing watersheds are similar in size (~10-40 hectares), have relatively uniform characteristics (e.g., soils, vegetation, geology, atmospheric deposition), are lined with watertight bedrock and glacial till, and are representative of the surrounding northern hardwood forest that comprises much of the northeastern United States and Canada. Sugar maple, yellow birch, and American beech comprise the dominant forest types at Hubbard Brook, with inclusions of spruce and fir on ridge tops and hemlock and white pine in lower-lying and riparian areas. Retreating glaciers approximately 14,000 years ago left deposits of unconsolidated till that vary widely in composition and depth. Soils are derived solely from this till and are predominantly Typic Haplorthods with sandy loam textures and high infiltration capacities.
The uniformity allows for comparisons to be made between watersheds, the watertight bedrock makes quantitative hydrologic and elemental budgets possible, and the similarity to surrounding ecosystems allows for extrapolations of results to a broader area. For these reasons as well as many logistical ones (e.g., ownership and administrative control), these watersheds are ideal for conducting long-term ecosystem experiments.
The HBES, co-founded in 1963 by Drs. Gene E. Likens, F. Herbert Bormann, Noye M. Johnson, and Robert S. Pierce, is the site where the phenomenon of acid rain was first demonstrated. Acid rain is formed when fossil fuels, such as coal or oil, are combusted for the production of electricity, releasing oxides of nitrogen and sulfur into the atmosphere.
A primary concern with these types of pollutants is their transboundary nature. That is, the pollutants responsible for acid rain in the New England region of the United States often originate in the Midwest – the location of many fossil fuel power plants. These pollutants are then transported by winds and deposited through precipitation as acid rain, causing damage to New England forests, lakes, and buildings.
Although noted for the discovery of acid rain and its early focus on hydrology, the scope of research at the HBEF has widened considerably since the site’s establishment. In addition to hydrology, current research focuses on vegetation, animals, soil, soil biota, and geology. These studies rely heavily on long-term environmental observations through the collection, synthesis, and analysis of data. This method is important for determining trends in and relationships between environmental processes, as well as the relationship between environmental and human-induced phenomena.
The White Mountain National Forest is also a popular recreational destination. The White Mountain ranges are home to the highest mountains in the northeastern United States including the highest, Mount Washington, as well as Mounts Adams, Jefferson, Monroe, and Madison. The New Hampshire segment of the Appalachian Trail, a popular hiking destination, is located mainly within the National Forest.