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A pygmy forest is a forest which, for pedological and geological reasons, contains only miniature trees. Pygmy forests may occur over various world locations with notable occurrences at the Ross of Mull on the Isle of Mull in Scotland, as example locations.
In the case of coastal Pygmy forests in northern California and Oregon, the formation began with a series of marine terraces and should be viewed as part of that formation. A combination of uplift and changes in ocean level formed a system of terraces, resulting in an “ecological staircase,” with each terrace approximately 100,000 years older than the one below it and supporting a distinct association of soils, microbes, plants, and animals. A dune being pushed farther away from the coast by fluctuating sea levels solidified and slid under the one before it, raising the terraces. Pioneer plant communities colonized and took over the young terrace. The succession of plant communities that repeated on each terrace eventually formed a very specific podzol known as the Blacklock series, which offers an inhospitable environment for species and greatly stunts further growth on the terrace. Part of this soil profile includes an underlying clay or iron hardpan. Each terrace is relatively level and many are footed by paleo-dunes. Drainage is poor at best on these stairs and plants sit in a bath of their own tannins and acids for much of the wet season. Plant communities on this terrace have reacted to limited root mobility and acidic soil by evolving stunted forms. Remnants of ecological staircases doubtless exist, however most have been destroyed for development or logging.
Examples of high-terrace podzol pygmy forests include:
- Mendocino Pygmy Forest in Mendocino County, California, for example, is an oligotrophic community caused by podzolized (nutrient-poor, highly acidic) soils. The forest flora is dominated by dwarfed Bishop pine, Bolander pine (a variety of shore pine), and Mendocino cypress. The latter two species are endemics to the pygmy forest. Bishop pine occurs in both dwarfed and full size form, the latter being trees who's roots have broken through the hardpan layer into the more fertile soil beneath. This forest is found in several discontinuous areas, with significant portions on the following public lands:
- Jug Handle State Natural Reserve, where it is the feature of the highest portion of the Ecological Staircase Trail.
- Russian Gulch State Park.
- Jackson Demonstration State Forest includes a large pygmy forest area east of the towns of Mendocino and Casper.
- The Hans Jenny Pygmy Forest Reserve, comanaged by the University of California Natural Reserve System and The Nature Conservancy.
- The Van Damme State Park pygmy forest, designated a National Natural Landmark. A self-guided nature trail built entirely on an elevated walkway forms a short loop through the site.
- Salt Point State Park in Sonoma County, California has a much smaller pygmy forest and a fifth terrace prairie ranging from 900 to 1000 feet and formerly supporting elk populations. Like the Mendocino forest, the dominant trees are also Bishop pine, Bolander pine, and Mendocino cypress. Most of Salt Point is on the northernmost portion of the Salinian Block and the terrace staircase drops suddenly into the gulch that lies over the San Andreas fault.
- SFB Morse Botanical Reserve in the Del Monte Forest of the Monterey Peninsula is centered on the small Huckleberry Hill pygmy forest of Bishop pine and Gowen cypress, in the middle of a more extensive forest of native Monterey pine. Bishop pine, which tolerates extreme podzol conditions better than Monterey pine, is found in the most heavily podzolized areas, with a zone of Bishop pine/Monterey pine hybrids dominating the less heavily podzolized area.
Soil chemistry and effect on plant growth
Analyses of pygmy forest soils show low levels of macro— and micro—nutrients, and high levels of exchangeable aluminum, which limits the ability of plants to grow. Low pH conditions support formation of an iron hardpan, preventing the trees from setting deep roots and preventing internal drainage of soil water.
As a result, the pine trees in the area are rarely more than three or four feet high, in a sort of natural bonsai effect. Many of the tree trunks, though only an inch thick, contain 80 or more growth rings. Only yards away, but with younger soils, the same species of tree grows many dozens of feet high.
Stunted tree growth can also occur in some cases of highly alkaline soils such as the Stora Alvaret or Great Alvar formation on the island of Öland in Sweden. In that area there are certain extents of pygmy tree growth and also areas devoid of trees entirely with many associations of rare species, due to the unique soil chemistry.
Other examples of California pygmy forests
- Elfin Forest Natural Area - El Moro Elfin Forest — 90 acre State Nature Reserve of 'pygmy oaks' (Coast live oak (Quercus agrifolia ). Located on the southeastern shore of Morro Bay, in Los Osos of coastal San Luis Obispo County. A raised wooden boardwalk loops through and around the forest, with viewing platforms.
- Cuesta Ridge Elfin Forest — in the Cuesta Ridge Botanical Special Interest Area, on western Cuesta Ridge of the Santa Lucia Range, in San Luis Obispo County. A pygmy Sargent Cypress (Cupressus sargentii) forest, where serpentine soil stunts growth. Protected within the 1,334 acre Cuesta Ridge Botanical Special Interest Area, in the Santa Lucia Ranger District of the Los Padres National Forest.  
- Dwarf Cupressus Preserve — a second West Cuesta Ridge grove of the pygmy cypress forest (Cupressus sargentii), managed by the Land Conservancy of San Luis Obispo County.
- Henry Cowell Redwoods State Park — select pygmy forest locales in the Santa Cruz Mountains, near Santa Cruz, in Santa Cruz County.
- Mount Tamalpais dwarf forest — a forest of small Cupressus pigmaea trees. The mountain’s serpentine soil stunts the growth of these trees, causing them to mature when only a few feet tall. On Old Stage Road, 0.5 miles northeast of the Bootjack Picnic Area. 
- San Geronimo Ridge — just south of Whites Hill in Marin County.
- Hood Mountain — near Santa Rosa in Sonoma County. A pygmy cypress forest dominated by Sargent's Cypress (Cupressus sargentii) and Arctostaphylos species can be found on the northwest slopes.
- C.Michael Hogan, (2011) Sea of the Hebrides. Eds. P. Saundry & C.J.Cleveland. Encyclopedia of Earth. National Council for Science and the Environment. Washington DC.
- California State Parks of San Luis Obispo Coast: El Moro Elfin Forest . accessed 5.25.2012
- USFS: Cuesta Ridge Botanical Special Interest Area
- Los Padres National Forest, Santa Lucia Ranger District: Cuesta Ridge
- LCSLO-Land Conservancy of San Luis Obispo County — Land Conservation . accessed 6.1.2012
- Golden Gate National Parks Conservancy