The San Dimas Experimental Forest (SDEF) is managed by the USDA Forest Service, Pacific Southwest Research Station, as a field laboratory for ecosystem and watershed studies in chaparral and related Mediterranean-climate ecosystems. From its establishment in 1933, the SDEF has been a center for hydrologic research in mountain watersheds.  This research has included intensive monitoring of precipitation and water yield in mountainous terrain and studies that manipulated the natural vegetation across watersheds to maximize water yield.  More recently research has emphasized the impact of wildland fire on watershed processes and air quality, the effects of chronic air pollution on stream-water quality and the biogeochemistry of nitrogen, processes and rates of soil development and erosion, patterns in plant community development, avian population dynamics, and remote sensing of fire and ecosystem processes.  Research and environmental monitoring at the SDEF have developed an extensive database on chaparral ecology and mountain hydrology and climate.

The U.S. Man and the Biosphere Program has designated the SDEF as a Biosphere Reserve.  SDEF also includes the Fern Canyon Research Natural Area, which is part of the Forest Service natural reserve system.

Williams Fire The San Dimas ecosystem was reset September 23-27, 2002 as the Williams Fire burned through 42 year-old chaparral.

Post-fire Images of the area of the Williams Fire were collected by the FireMapper instrument flown in the PSW research aircraft on 18 December, 2002.

Fire severity, water quality, and post-fire debris production

Severe fires in chaparral watersheds subject to air pollution from metropolitan Los Angeles mobilize accumulated nitrogen and cause stream water to be polluted with nitrate (NO₃^- ) at concentrations exceeding the Federal water quality standard. Fires of moderate intensity produced a more subdued response in stream discharge and soil nitrification and less than one-seventh the NO₃^- loss observed after severe burning.

Fire emissions

Wild fire emissions to the atmosphere are an acute source of particulates, hydrocarbons, and greenhouse gases. The first whole-plume measurements of emissions from chaparral fires were made by aircraft at San Dimas in the Lodi Canyon prescribed fires of 1986 and 1987.

Water Quality

Emissions of nitrogen oxides in the South Coast Air Basin of southern California are among the most extreme in the nation. Resulting atmospheric nitrogen deposition to vegetation at San Dimas, as measured by canopy throughfall of nitrate and ammonium, has been at record levels nationally and is apparently a primary source of nitrate pollution in stream water there.

Water yield

The San Dimas Experimental Forest, one of the oldest natural hydraulic laboratories in the nation, was established to determine the value of chaparral and associated forests for watershed protection and to provide a basis for management to obtain the maximum beneficial yield of water.

Chaparral ecology

Fire is an ecosystem property, rather than an exogenous force in southern California chaparral, which interacts with processes of drought-mediated canopy development, production, and mortality to affect stability of community composition. Despite adaptations to survive prolonged drought stress and burning, recurrent fire now threatens the stability of the ecosystem.
SDEF 1960, USFS photo
SDEF 1980, USFS photo by P. Riggan

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"This web page is dedicated to the memory of Forest Manager Chuck Colver."

Forest Manager Chuck Colver at Brown's Flat, 1981, USFS photo