Hubbard Brook Experimental Forest

Hubbard Brook Experimental Forest (HBEF) was established in 1955 as a major center for hydrologic research in New England. The site is located within the boundaries of the White Mountain National Forest in central New Hampshire. The 3,138-ha, bowl-shaped Valley has hilly terrain, ranging from 222 to 1,015 m altitude. During the first eight years following establishment a network of precipitation and stream-gauging stations, weather instrumentation, as well as soil and vegetation monitoring sites on small experimental watersheds were developed. Data from these installations combined with several initial studies formed the hydrometeorologic foundation for much of the future research at the HBEF. The major emphasis in these early studies was to determine the impact of forest land management on water yield and quality, and flood flow.

The Hubbard Brook Ecosystem Study (HBES) originated in 1960 with the idea of the small watershed approach to study element flux and cycling. A joint research program between the USDA Forest Service and Dartmouth College was established by a cooperative agreement in 1963. Also that year, funds from a grant from the National Science Foundation (NSF) provided the start of the HBES research program. Support from the USDA Forest Service and the NSF has been continuous since that time. In 1988 the HBEF was designated as a Long Term Ecological Research (LTER) site by the National Science Foundation. On-going cooperative efforts among diverse educational institutions, private institutions, government agencies, foundations and corporations have resulted in one of the most extensive and longest continuous data bases on the hydrology, biology, geology and chemistry of natural ecosystems.

Climate

Annual precipitation averages about 1,400 mm, with one-third to one-quarter as snow. Approximately 111 separate storms occur each year. A snowpack usually persists from mid-December until mid-April, with a peak depth in March of about 1,020 to 1,270 mm, having about 250 to 300 mm of water content. January averages about –9oC, and long periods of low temperatures from –12oC to –180C are common. The average July temperature is 18oC. The average number of days without killing frost is 145; however, the growing season for trees is considered to be from 15 May to 15 September. The estimated annual evapotranspiration is about 500 mm.

Soils

Soils at Hubbard Brook are predominantly well-drained Spodosols, more specifically, Typic Haplorthods, derived from glacial till, with sandy loam textures. There are no residual soils. These soils are acidic (pH about 4.5 or less) and relatively infertile (base saturation of mineral soil ~ 10%). A 20- to 200-mm thick forest floor layer is present, except where the soil surface has been disturbed by fallen trees. Soil depths, including unweathered till, average about 2.0 m surface to bedrock, although this is highly variable. Soil on the ridgetops may consist of a thin accumulation of organic matter, resting directly on bedrock. The separation between the pedogenic zone and the virtually unweathered till and bedrock below is distinct. Depth to the C horizon averages about 0.6 m. At various places in HBEF, the C horizon exists as an impermeable pan. Rocks of all sizes are scattered throughout the soil profile. In many locations boulder fields are prominent features.

Vegetation types

The area is entirely forested, mainly with deciduous northern hardwoods: sugar maple (Acer saccharum), beech (Fagus grandifolia), and yellow birch (Betula allegheniensis), and some white ash (Fraxinus americana) on the lower and middle slopes. Other less abundant species include mountain maple (Acer spicatum), striped maple (Acer pensylvanicum), and trembling aspen (Populus tremuloides). Red spruce (Picea rubens), balsam fir (Abies balsamea), and mountain paper birch (Betula papyrifera var. cordifolia) are abundant at higher elevations and on rock outcrops. Hemlock (Tsuga canadensis) is found along the main Hubbard Brook. Pin cherry (Prunus pensylvanica), a shade intolerant species, dominates all sites for the first decade following a major forest disturbance. Logging operations ending around 1915-1917 removed large portions of the conifers and better quality, accessible hardwoods. The present second-growth forest is even-aged and composed of about 80 to 90% hardwoods and 10 to 20% conifers.

Long-term Monitoring

A strength of the HBES is the long-term monitoring program. The monitoring program at Hubbard Brook shows that short-term observations are often misleading and that decades may be required to detect real changes in complex ecosystems. The long-term record at the HBEF provides: 1) insight into ecosystem function, 2) empirical data for testing models and generating hypothesis, 3) a record of extreme or unusual events, and 4) information that is relevant to regional, national and global issues.

Current long-term monitoring data sets developed through the HBES

Physical/Hydrologic Monitoring
     Instantaneous streamflow (9 stations)
     Daily precipitation (24 stations)
     Class A weather station data
     Weekly snow depth on snow courses
     Daily soil temperature and moisture
Air Chemistry (SO₂, HNO₃, particulates, ozone)
Mirror Lake
     Instantaneous streamflow (3 inlets, outlet)
     Daily precipitation (2 stations)
     Weekly chemistry (3 inlets, outlet)
     Bi-monthly limnology (temp, chemistry, plankton)

Solution Chemistry
     Weekly bulk precipitation (6-10 stations)
     Monthly soil solution W5, W6
     Weekly stream at weirs of W1-9
     Monthly stream within W5, W6
Organisms
     Bird populations
     Phytophagous insect populations
     W2, W4, W5, W6 Vegetation, biomass, chemistry
Soils
     Forest floor mass, chemistry (W6, W5; 5-yr intervals)
     Chemical and physical properties from soil pits (W5)
     Chemical and physical properties from soil bags

Experimental Watershed Manipulations

Watershed 2

Watershed 4

Watershed 5

Experimental manipulation is a research approach that has been used extensively at Hubbard Brook. A number of whole watershed, stream and lake manipulations have been conducted to test research hypotheses, obtain quantitative information on pertinent environmental issues and to validate process-related formulations used in simulation models. Whole ecosystem manipulations conducted at Hubbard Brook include:

Watershed	Size (ha)	Year Gauged	Treatment
1	11.8	1956	Calcium manipulation in 1999. About 1.2 metric tones/ha of calcium (as wollastonite CaSiO3) applied.
2	15.6	1957	Clear felled in winter 1965-66; no products removed; treated with herbicides summers of 1966, 1967, 1968. Left to regrow from 1969.
4	36.1	1961	Clear-cut to a 2 cm minimum diameter, by strips in three phases, 1970, 1972, 1974. Timber products removed.
5	21.9	1962	Whole-tree clear-cut to 5 cm diameter, 1983-1984. Timber products removed.
6	13.2	1963	None; biogeochemical reference watershed.
101	12.1	1970	Clear-cut to a 5 cm minimum diameter, as a block in 1970. Timber products removed. Note: streamflow quantity is not monitored, only water quality.

Current Projects at Hubbard Brook Experimental Forest

NSF – LTER (Charles Driscoll, Syracuse & Timothy Fahey, Cornell) and LTREB (Gene Likens, Institute of Ecosystem Studies)
The role of calcium supply in regulating the structure and function of base-poor forest and aquatic ecosystems (Charles Driscoll, Syracuse)
Animal population and community studies (Richard Holmes, Dartmouth College)
Colder soils in a warmer world: A snow manipulation in a northern hardwood forest ecosystem (Peter Groffman, Institute of Ecosystem Studies)
Stream Ecosystem Research (Gene Likens, Institute of Ecosystem Studies)
A spatial model of soil parent material (Scott Bailey, USFS)
Modeling effects of acid deposition, forest disturbance and soil chemistry on forest production and stream water quality (John Aber, University of New Hampshire)
Use remote sensing for measurement of canopy nitrogen and calcium content, and estimation of forest production and stream chemistry (John Aber, University of New Hampshire)
Landscape-scale controls on N retention and N gas fluxes in the Hubbard Brook Valley (Peter Groffman and Gary Lovett, Institute of Ecosystem Studies)
Nutrient uptake at the Ecosystem Scale (Ruth Yanai, SUNY-ESF)
Carbon and calcium controls on microbial biomass and invertebrate grazers (Melany Fisk, Appalachian State)
Does the small watershed chemical paradigm work throughout the entire HBEF valley? (Gene Likens, Institute of Ecosystem Studies)
The link between soils and plants: A 15N of plant available N (Linda Pardo, USFS)
sponse of northern hardwood forests to nutrient perturbation (Chris Eagar, USFS)
Edaphic controls on the structure and function of the northern hardwood forest (Scott Bailey, USFS)
Vegetation dynamics and primary productivity (Thomas Siccama, Yale)
Hubbard Brook Sandbox Studies (Herb Bormann, Yale and Dean Wang, UVM)

Major research accomplishments and impacts on management

Small watershed technique for studying biogeochemistry
Factors regulating nutrient flux and cycling in northern hardwood forests
First documentation of acid rain in North America
Effects of forest harvesting disturbance on water quality and quantity
Long-term effects of acid rain on soil nutrient pools and streamwater chemistry
Relationship of interior forest bird populations and communities to forest structure and development
Development and application of ecosystem process models: 1) hydrological, 2) forest growth and development, and 3) soil nutrient processes

Facilities

The Robert S. Pierce Ecosystem Laboratory provides 835 m2 of space, including six offices, four laboratories, one conference room, six dormitory rooms, a kitchen, baths and showers. A sample archive building was constructed in 1990 to house and archive samples of soil, water, plant tissue, and other materials. In addition, there are 280 m2 of maintenance, storage, garage and shop facilities. There are 16 km of gravel roads within the Experimental Forest. A trail system allows access to major research installations such as precipitation stations.