m³) of timber had been harvested from the valley. Soils Soil is predominantly well-drained spodosol derived from glacial till, with sandy loam textures, combining to produce an evident, but narrow E horizon. The forest floor is characterized by the complete suite of taxonomic subhorizons, has been classified as mor type humus, with mull occurring beneath maple stands at lower elevations (). It is acidic (pH about 4.5 or less) and relatively infertile for agricultural purposes. Aluminum and iron are preferentially leached from the upper soil horizons to an underlying layer(s) that is characteristic of the soil order. Hence, silica is retained and at times mixes with the forest floor. Soil depths are highly variable, with shallow strands of organic matter comprising the entire profile at higher elevations (folist) or underlain by sandy unsorted material (podzol). Climate Annual precipitation averages about , with one-third to one-quarter as snow. January averages about -9 °C and the average July temperature is 18 °C. The forest averages 145 frost-free days per year. Areas of research Hydrology, including ecosystem water flow, snowfall analysis, and long-term ice-in/ice-out measurements Environmental factors encouraging or restricting tree growth, and effects of deforestation on mineral flux Effects of environmental changes on bird behavior and insect population, especially regarding reproductive capacity Effects of acid rain and resultant soil mineral changes on micro-environments of plant root systems Cycling of Nitrogen, Sulfur, Phosphorus, Mercury, Calcium, and Carbon, and effects of pollution on flux of these and other minerals Hubbard Brook Research Foundation The Hubbard Brook Research Foundation supports the work of the Hubbard Brook Ecosystem Study, which is conducted at the USDA Forest Service's Hubbard Brook Experimental Forest in New Hampshire's White Mountain National Forest. HBRF supports research by maintaining facilities for housing, meetings, and laboratory work. The Foundation also helps transmit the findings of the Hubbard Brook Ecosystem Study to policymakers, opinion leaders, and other members of the public through its Science Links program, which translates science from peer-reviewed scientific articles and conducts a variety of education and outreach activities. Annual symposium Each summer, Hubbard Brook scientists and experts from afar gather at the base station for a 2-day colloquium to present and discuss ongoing research. Approximately 150 scientists and students attend the program, which features eighty-odd 10-minute presentations in which participants openly criticize and contribute new ideas to each presenter's findings. References External links Hubbard Brook Ecosystem Study website Hubbard Brook