Experimental Forest: A Vision

The San Dimas The San Dimas

United States Department of Agriculture Forest Service

Pacific Southwest Research Station

United States

Department of

Agriculture

Forest Service

Pacific Southwest

Research Station

PSW-MISC-78
“Few other mountain areas of comparable size on earth have

been as thoroughly and painstakingly examined, as has the

San Dimas Experimental Forest. There is, quite literally, no

plant, no type of soil, no rock, no form of animal life that is

unknown to the forest sleuths of Tanbark Flats.” 

Edward Colman, forester, 1938

Cover image: San Dimas Canyon
3 Our Vision

4 A Changing Mission

4 Research Questions for San Dimas Experimental Forest

5 Integrating Social and Riparian Components into San Dimas 

Experimental Forest Research

6 Why Here?

8 Management Challenges

9 Next Steps

Fern Canyon Research Natural Area, within San Dimas Experimental Forest
“Wedged snugly between the lower

reaches of San Gabriel and San

Antonio canyons is a 32-square

mile rectangle of mountain country

little known to most southern

Californians. Here, enclosed by lofty

ridges on three sides, are the

watersheds of Little Dalton, Big

Dalton and San Dimas Canyons, a

sinuous region of chaparral-coated

hills, little forested flats and

delightful creeks luxuriant with live

oak, alder, bay and sycamore. Here

lies the San Dimas Experimental

Forest, an extensive outdoor

laboratory dedicated to learning

about soil, vegetation and erosion in

mountain watersheds.” 

John Robinson, 

San Gabriel Mountain historian, 1985
Our Vision

The San Dimas Experimental Forest (SDEF) offers a unique oasis of opportunity for

providing an internationally recognized wildland-urban interface research facility

where all land within the proclaimed boundary is used by federal, state, university, and

international scientists to develop information and solutions for current and future

resource management questions; where outdoor education is provided on the chaparral

and woodland ecosystems adjacent to the rapidly growing Los Angeles Basin; and where

local communities benefit from the activities at the experimental forest. We envision the

SDEF as the preeminent facility for natural resource science research in Mediterraneantype ecosystems.

The SDEF is managed by the USDA Forest Service Pacific Southwest Research Station

(PSW) as a field laboratory for ecosystem, watershed, and natural resource science

research in chaparral and related Mediterranean-climate ecosystems. Since 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 manipulation of the natural vegetation across watersheds

to maximize water yield. More recently, research has investigated the impact of wildland

fire on watershed processes and air quality and the effects of chronic air pollution from

the Los Angeles basin on stream water quality and the biogeochemistry of nitrogen. Other

recent experiments have studied 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.

3
Integrating Social and Riparian Components into SDEF

Research

The SDEF is a hub for Wildland Urban Interface research studying not only the effects

of people on the landscape studied, but also the values of the landscape to people.

Instead of serving as an inviolate preserve, SDEF will serve three purposes: (1) to serve

as an experimental area to reconcile people’s demand for recreation and the need to

maintain functioning ecosystems, (2) to bring knowledge of the past to the needs of the

future, and (3) to model ways to involve the various sectors of the wildland urban

interface in land management planning. 

We will study community involvement and participatory decisionmaking in planning

and implementing the vision for SDEF, leading to collaborative planning models with

diverse urban communities for the urban national forests in southern California and

throughout the world. We will also study approaches for improving policy/issue

communications with affected publics, forest interpretation, conservation education, and

postfire education to improve community understanding of forest management. Future

recreation will study the recreation needs of urban populations and will examine public

views on natural spaces and their management. 

Small riparian areas in southern California are critical habitat for many species and

have been severely altered by human use, including recreation. We will investigate

techniques to restore riparian function in the lower reaches of the West and Main Forks

of San Dimas Creek (where significant changes have occurred because of use over the

past 90 years) and investigate how riparian areas recover from the impacts of roads and

recreational residence tracts. We will implement a landscape-scale research project to

determine the appropriate use of prescribed fire to manage chaparral in a wildlandurban interface setting. The new emphases on social science and riparian restoration

will be integrated with long-term research on air pollution, water quantity, water

A Changing Mission

The current mission of the San Dimas Experimental Forest is to serve as a field

laboratory where scientists and managers can gain basic knowledge of physical,

biological, and social science that can be applied to issues important to the

southern California national forests and other wildlands. Through limited tours

and scheduled visits, it also serves as an outdoor learning center for local youth.

In the future, research will continue on these vital issues, but we will increase our

capacity to study integrated watershed management from the forest through the city

to the sea. Studying fire in the urban interface will be a priority focus area. Our

mission will expand to include research related to the social and recreational

components of the complex southern California environment. The SDEF’s utility as

a field laboratory will also be expanded to include public and school educational

opportunities, interpretive services, and environmental education curriculum.

Research Questions for SDEF

Originally, SDEF was created to answer hydrologic questions, such as how to get

more water from the watershed with management. Over time, the value of SDEF

to answer a broader array of questions was recognized.

Research economists found that the costs of erosion abatement are extremely

high. The SDEF is ideally suited to test the hypothesis that management of

chaparral can indeed reduce sedimentation.

Fire is an integral part of ecosystem functions. The SDEF is an outdoor laboratory

to answer questions about fire ecology and fire effects, as well as restoration

effectiveness following fires. 

In addition to physical and biological research, SDEF is strategically located to

address social and urban issues with research and environmental education.

4 5

Horse Saddle Canyon Bell Canyon Tanbark Flats Browns Flats in Fern Canyon RNA

Big Dalton Reservoir

Current research is confined to the green areas located above the

perennial streams. Riparian areas affected by roads and the

recreational residence tracts are shown in orange.
quality, chaparral ecology (plant and animal), weather, erosion and sedimentation, and postfire

rehabilitation. New and refurbished federal buildings within the SDEF boundary will be used to

accomplish these activities.

Facilities at the SDEF include the historical Tanbark Flats Research Station; operating streamwater

discharge gauging stations in Bell and Volfe Canyons; inoperable streamwater discharge gauging

stations in West Fork and Main Fork of San Dimas Creek; sediment collection basins in Bell Canyon;

a network of precipitation gauges; the historical Tanbark Flats lysimeters, which have recently been a

focus of soil development studies; and a network of roads and trails. Tanbark Flats facilities include

living quarters and barracks, a small laboratory, mess hall, and shops. Facilities for stream gauging

could be restored below small watersheds in Fern Canyon, lower Bell Canyon and the West Fork of

San Dimas Canyon, and in the main Fern and Monroe Canyons. Thirteen recreational residences

remain in lower San Dimas Canyon since the Williams Fire--four in the Main Fork and nine in the

West Fork, accessed by forest roads.

6

SDEF mess hall, 1930s

Volfe Canyon gauging station

Construction of the the lysimeters

Gauging station, 1930s

SDEF meeting, 1930s
Why Here?

Located in the foothills of the San Gabriel Mountains, the SDEF is the largest chaparral

experimental forest in the United States. It also contains the Fern Canyon Research

Natural Area, which is part of the Forest Service natural reserve system. The U.S. Man

and the Biosphere Program has designated the SDEF as a biosphere reserve. Biosphere

reserves are known as “landscapes for learning” and “laboratory regions of sustainable

development” because of their role in associating research and education with

conservation and development issues. They provide a means for integrating conservation,

research and monitoring, education and training, and involving local populations in

conservation and development issues in areas of outstanding ecological, scientific, and

educational importance.

The San Dimas-Big Dalton watershed was chosen as an experimental forest over the many

other watersheds in southern California for several reasons. First, its vegetation pattern

was typical of the southern California mountains: chaparral in the lower and middle

reaches, streamside woodland in the canyons, and conifers on the higher ridges and flats.

The region is separated from the main mass of the San Gabriel Mountains by the deep San

Gabriel and San Antonio Canyons, an isolation factor considered ideal for controlled study

of water flow. Further, the two major drainages contain numerous small tributaries suitable

for a variety of experiments. And lastly, both San Dimas and Big Dalton Canyons were

harnessed by L.A. County flood-control dams, providing controls for measurement of

water flow. No other similar-sized area in southern California possessed all these

advantages (Lawrence W. Hill, The San Dimas Experimental Forest, 1963).

7

San Gabriel River Watershed to the Pacific
Management Challenges

Today the burgeoning population growth of the Los Angeles basin is placing increasing demands on

national forests for a variety of resources. Recreation use of national forests has skyrocketed, as has

the complex interface between land covered with homes and the remaining native vegetation.

Riparian areas are popular locations for many types of recreation. Shrinking areas of habitat on

private lands mean that public lands, including national forests, are the last refuge for many rare

species. Controversy exists over fire management in chaparral. Billions of dollars are spent to get

water into and out of the Los Angeles urban area served by the San Gabriel River system. These

issues are increasing in importance on public lands near urban areas nationwide, with the national

forests of southern California in the forefront.

The SDEF is uniquely situated to use innovative research approaches to address these management

challenges through social, biological, and physical science. However, the presence of private inholdings,

forest development roads, and the recreation residence tracts in the West and Main Forks of San Dimas

Creek significantly limit the ability to conduct needed research. The recreation residence tracts and forest

development roads within and adjacent to the riparian area pre-date the establishment of the

experimental forest. Their location is not conducive to current Forest Service practice or standards, nor

do they meet the vision of the experimental

forest in meeting educational and scientific

needs and demands. The tracts of land that

support the recreation residence are part of

the experimental forest. The Angeles National

Forest administers the recreation residence

permits only. Today, there is increasing

8

Access to recreational residence tracts

washed out by flooding within the riparian

areas, 2003-2005.

Developed area south of Big Dalton

Road wash out in San Dimas,

early 1930s.

West Fork road lost to

flood waters within the

riparian area.
recognition that the SDEF is unique as part of a national network of experimental forests, that it

needs a more controlled environment to utilize its full potential for a variety of research

studies, and that to achieve that purpose it must be restored and maintained.

Next Steps

Working with our partners in local communities, other agencies, and universities, the SDEF

provides an exceptional site to: 

• Better define the objectives of research in the San Dimas Experimental Forest and 

how that research will add to the body of knowledge about Mediterranean ecosystems 

gained through 70 years of data collected at the SDEF.

• Determine our role in adding benefits to local communities.

• Explore the relationship between urban populations and wildland recreation areas.

• Better define the role of wildland watersheds in the integrated management of the water

supply of the greater Los Angeles Basin.

• Pursue opportunities to purchase private 

inholdings, discontinue use of recreation 

residence tracts, and decommission roads 

along these tracts to restore use of the land 

and evaluate impacts and recovery of the 

West and Main Forks of San Dimas Creek.

9

Sunset in Fern Canyon
The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on the basis of race, color, national origin, age, disability, and where

applicable, sex, marital status, familial status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because all or part of an

individual's income is derived from any public assistance program. (Not all prohibited bases apply to all programs.) Persons with disabilities who require alternative

means for communication of program information (Braille, large print, audiotape, etc.) should contact USDA's TARGET Center at (202) 720-2600 (voice and TDD). To file

a complaint of discrimination, write to USDA, Director, Office of Civil Rights, 1400 Independence Avenue, S.W., Washington, D.C. 20250-9410, or call (800) 795-3272

(voice) or (202) 720-6382 (TDD). USDA is an equal opportunity provider and employer. 

“Western man has often attempted to improve his environment. Nowhere is this more evident than in the work

of the San Dimas Experimental Forest. This extensive outdoor library, dedicated to learning about the influences

of geology, soil and vegetation on mountain watersheds occupies almost all of the San Dimas and Big Dalton

watersheds. The knowledge gained in almost a half century of forest research has benefited not only southern

California but the whole world.”

John Robinson, San Gabriel Mountain historian, 1985

www.fs.fed.us/psw/ef