A pygmy forest is a forest

Forest

A forest, also referred to as a wood or the woods, is an area with a high density of trees. As with cities, depending where you are in the world, what is considered a forest may vary significantly in size and have various classification according to how and what of the forest is composed...

 which, for pedological

Pedology (soil study)

Pedology is the study of soils in their natural environment. It is one of two main branches of soil science, the other being edaphology...

 and geological

Geology

Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...

 reasons, contains only miniature trees. Pygmy forests may occur over various world locations with notable occurrences being noted in the literature of the: California coastal terraces and inner coastal mountains of Northern California

Northern California

Northern California is the northern portion of the U.S. state of California. The San Francisco Bay Area , and Sacramento as well as its metropolitan area are the main population centers...

; the Ross of Mull on the Isle of Mull in Scotland, as example locations.

A variant of the pygmy forest is sometimes called elfin forest

Elfin forest

-Residential community:Elfin Forest is an unincorporated residential community of San Diego County in the foothills of the Santa Rosa Mountains. The quiet grouping of homes is southwest of Escondido and according to the USGS it is located at in the Escondido zip code of 92029...

 in parts of Southern California

Southern California

Southern California is a megaregion, or megapolitan area, in the southern area of the U.S. state of California. Large urban areas include Greater Los Angeles and Greater San Diego. The urban area stretches along the coast from Ventura through the Southland and Inland Empire to San Diego...

, Mexico

Mexico

The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

, and Central America

Central America

Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...

.

California examples

Several species of trees, such as Cupressus pigmaea

Cupressus pigmaea

Cupressus pigmaea is a taxon of disputed status in the genus Cupressus endemic to certain coastal terraces and coastal mountain ranges of Mendocino and Sonoma Counties in northwestern California...

, can be found in the Mendocino County, California

Mendocino County, California

Mendocino County is a county located on the north coast of the U.S. state of California, north of the greater San Francisco Bay Area and west of the Central Valley. As of the 2010 census, the population was 87,841, up from 86,265 at the 2000 census...

 and Sonoma County, California

Sonoma County, California

Sonoma County, located on the northern coast of the U.S. state of California, is the largest and northernmost of the nine San Francisco Bay Area counties. Its population at the 2010 census was 483,878. Its largest city and county seat is Santa Rosa....

 pygmy forests, notably the vulnerable species Mendocino Cypress. A pygmy forest is located on San Geronimo Ridge just south of Whites Hill in Marin County, California

Marin County, California

Marin County is a county located in the North San Francisco Bay Area of the U.S. state of California, across the Golden Gate Bridge from San Francisco. As of 2010, the population was 252,409. The county seat is San Rafael and the largest employer is the county government. Marin County is well...

. A pygmy cypress forest

Cypress forest

A Cypress forest is a western USA plant association typically dominated by one or more cypress species. Example species comprising the canopy include Cupressus macrocarpa. In some cases these forests have been severely damaged by goats, cattle and other grazing animals...

 dominated by Sargent's Cypress (Cupressus sargentii

Cupressus sargentii

Cupressus sargentii is a species of conifer in the Cupressaceae family known by the common name Sargent's cypress. It is endemic to California, where it is known from Mendocino county southwards to Santa Barbara county. This taxon is limited to the Coast Range mountains. Like Mcnab Cypress, it...

) can be found on the northwest slopes of Hood Mountain

Hood Mountain

Mount Hood, also known as Hood Mountain is a mountain near the southeastern edge of Santa Rosa, California at the northeast of the Sonoma Valley and attains a height of . The originally name was Mount Wilikos, an Indian name meaning "willows."...

, near Santa Rosa

Santa Rosa, California

Santa Rosa is the county seat of Sonoma County, California, United States. The 2010 census reported a population of 167,815. Santa Rosa is the largest city in California's Wine Country and fifth largest city in the San Francisco Bay Area, after San Jose, San Francisco, Oakland, and Fremont and 26th...

 in Sonoma County. In good soil these trees can grow to 50 or 60 feet (18.3 m) high but in ultramafic soils such as serpentine

Serpentine soil

A serpentine soil is derived from ultramafic rocks, in particular serpentinite, a rock formed by the hydration and metamorphic transformation of ultramafic rock from the Earth's mantle....

 they are much shorter. The Land Conservancy of San Luis Obispo County

Land Conservancy of San Luis Obispo County

is a local nonprofit organization that has served San Luis Obispo County since 1984. Through voluntary and collaborative efforts the LCSLO works to protect and enhance lands having important scenic, agricultural, habitat and cultural values for the benefit of people and wildlife...

 manages a dwarf Cupressus

Cupressus

The genus Cupressus is one of several genera within the family Cupressaceae that have the common name cypress; for the others, see cypress. It is considered a polyphyletic group...

 preserve on Cuesta Ridge.

Van Damme State Park

The Jenny Pygmy Forest in Van Damme State Park

Van Damme State Park

Van Damme State Park consists of about of land in Mendocino County, California, near the town of Little River on State Route 1. It was named for Charles Van Damme , who was born in the area and purchased the land that is now the park with profits from a San Francisco ferry business...

, Mendocino County, California

Mendocino County, California

Mendocino County is a county located on the north coast of the U.S. state of California, north of the greater San Francisco Bay Area and west of the Central Valley. As of the 2010 census, the population was 87,841, up from 86,265 at the 2000 census...

, for example, is an oligotroph

Oligotroph

An oligotroph is an organism that can live in an environment that offers very low levels of nutrients. They may be contrasted with copiotrophs, which prefer nutritionally rich environments...

ic community caused by podzolized

Podsol

In soil science, podzols are the typical soils of coniferous, or boreal forests. They are also the typical soils of eucalypt forests and heathlands in southern Australia...

 (nutrient-poor, highly acidic) soils. It is a National Natural Landmark

National Natural Landmark

The National Natural Landmark program recognizes and encourages the conservation of outstanding examples of the natural history of the United States. It is the only natural areas program of national scope that identifies and recognizes the best examples of biological and geological features in...

, a designation of a national scope that identifies and recognizes the best examples of biological and geological features in the U.S.

Structure

Underlying this relatively inhospitable soil is a clay hardpan. 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.

The pygmy forest in this case formed on the oldest stable surface where soils are approximately 500,000 years old. Each terrace is relatively level, which prevents draining and allows rainwater to leach many of the nutrients away. Over time, this results in extremely high acidity.

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

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

 hardpan, preventing the trees from setting deep root

Root

In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...

s 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

Bonsai

is a Japanese art form using miniature trees grown in containers. Similar practices exist in other cultures, including the Chinese tradition of penjing from which the art originated, and the miniature living landscapes of Vietnamese hòn non bộ...

 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.

Alkaline soils

Stunted tree growth can also occur in some cases of highly alkaline soils such as the Stora Alvaret

Stora Alvaret

The Stora Alvaret is a limestone barren plain on the island of Öland, Sweden. Because of the thin soil mantle and high pH levels, a great assortment of vegetation is found including numerous rare species. Stora Alvaret has been designated as a World Heritage Site by UNESCO due to its...

 or Great Alvar formation on the island of Öland

Öland

' is the second largest Swedish island and the smallest of the traditional provinces of Sweden. Öland has an area of 1,342 km² and is located in the Baltic Sea just off the coast of Småland. The island has 25,000 inhabitants, but during Swedish Midsummer it is visited by up to 500,000 people...

 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

Rare species

A rare species is a group of organisms that are very uncommon or scarce. This designation may be applied to either a plant or animal taxon, and may be distinct from the term "endangered" or "threatened species" but not "extinct"....

, due to the unique soil chemistry.