Life zone

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The life zone concept was developed by C. Hart Merriam in 1889 as a means of describing areas with similar plant and animal communities. Merriam observed that the changes in these communities with an increase in latitude at a constant elevation are similar to the changes seen with an increase in elevation at a constant latitude. [1]

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The life zones Merriam identified are most applicable to western North America, being developed on the San Francisco Peaks, Arizona and Cascade Range of the northwestern USA. He tried to develop a system that is applicable across the North American continent, but that system is rarely referred to.

The life zones that Merriam identified, along with characteristic plants, are as follows:

The Canadian and Hudsonian life zones are commonly combined into a Boreal life zone.

This system has been criticized as being too imprecise. For example, the scrub oak chaparral in Arizona shares relatively few plant and animal species with the Great Basin sagebrush desert, yet both are classified as Upper Sonoran. However it is still sometimes referred to by biologists (and anthropologists) working in the western United States. Much more detailed and empirically based classifications of vegetation and life zones now exist for most areas of the world, such as the list of world ecoregions defined by the World Wide Fund for Nature, [2] or the list of North American ecoregions defined by the Commission for Environmental Cooperation. [3]

Holdridge

Holdridge life zone classification scheme. Although conceived as three-dimensional by its originator, is usually shown as a two-dimensional array of hexagons in a triangular frame. Lifezones Pengo.svg
Holdridge life zone classification scheme. Although conceived as three-dimensional by its originator, is usually shown as a two-dimensional array of hexagons in a triangular frame.

In 1947, Leslie Holdridge published a life zone classification using indicators of:

Biotemperature refers to all temperatures above freezing, with all temperatures below freezing adjusted to 0 °C, as plants are dormant at these temperatures. Holdridge's system uses biotemperature first, rather than the temperate latitude bias of Merriam's life zones, and does not primarily use elevation. The system is considered more appropriate to the complexities of tropical vegetation than Merriam's system. [4]

See also

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Biome Plants and animals associated with an environment

A biome is a collection of plants and animals that have common characteristics for the environment they exist in. They can be found over a range of continents. Biomes are distinct biological communities that have formed in response to a shared physical climate. Biome is a broader term than habitat; any biome can comprise a variety of habitats.

Chaparral Shrubland plant community in western North America

Chaparral is a shrubland plant community found primarily in the U.S. state of California, in southern Oregon, and in the northern portion of the Baja California Peninsula in Mexico. It is shaped by a Mediterranean climate and infrequent, high-intensity crown fires, featuring summer-drought-tolerant plants with hard sclerophyllous evergreen leaves, as contrasted with the associated soft-leaved, drought-deciduous, scrub community of coastal sage scrub, found often on drier, southern facing slopes within the chaparral biome. Three other closely related chaparral shrubland systems occur in central Arizona, western Texas, and along the eastern side of central Mexico's mountain chains (mexical), all having summer rains in contrast to the Mediterranean climate of other chaparral formations. Chaparral comprises 9% of the California's wildland vegetation and contains 20% of its plant species. The name comes from the Spanish word for place of the scrub oak, chaparro.

Alpine tundra Biome found at high altitudes

Alpine tundra is a type of natural region or biome that does not contain trees because it is at high elevation. As the latitude of a location approaches the poles, the threshold elevation for alpine tundra gets lower until it reaches sea level, and alpine tundra merges with polar tundra.

Mediterranean climate Type of climate

A Mediterranean climate or dry summer climate is characterized by dry summers and mild, wet winters. The climate receives its name from the Mediterranean Basin, where this climate type is most common. Mediterranean climate zones are typically located along the western sides of continents, between roughly 30 and 45 degrees north and south of the equator. The main cause of Mediterranean, or dry summer climate, is the subtropical ridge which extends northwards during the summer and migrates south during the winter due to increasing north–south temperature differences.

Great Basin Desert Desert in the United States

The Great Basin Desert is part of the Great Basin between the Sierra Nevada and the Wasatch Range. The desert is a geographical region that largely overlaps the Great Basin shrub steppe defined by the World Wildlife Fund, and the Central Basin and Range ecoregion defined by the U.S. Environmental Protection Agency and United States Geological Survey. It is a temperate desert with hot, dry summers and snowy winters. The desert spans a large part of the state of Nevada, and extends into western Utah, eastern California, and Idaho. The desert is one of the four biologically defined deserts in North America, in addition to the Mojave, Sonoran, and Chihuahuan Deserts.

Subtropics Geographic and climate zone

The subtropical zones or subtropics are geographic and climate zones located to the north and south of the tropical zone. Geographically part of the north and south temperate zones, they cover the latitudes between 23°26′11.6″ and approximately 35° in the northern hemisphere and in the southern hemisphere.

Chihuahuan Desert Desert ecoregion in Mexico and the United States

The Chihuahuan Desert is a desert and ecoregion designation covering parts of northern Mexico and the southwestern United States. It occupies much of West Texas, the middle and lower Rio Grande Valley, the lower Pecos Valley in New Mexico, and a portion of southeastern Arizona, as well as the central and northern portions of the Mexican Plateau. It is bordered on the west by the Sonoran Desert and the extensive Sierra Madre Occidental range, along with northwestern lowlands of the Sierra Madre Oriental range. On the Mexican side, it covers a large portion of the state of Chihuahua, along with portions of Coahuila, north-eastern Durango, the extreme northern part of Zacatecas, and small western portions of Nuevo León. With an area of about 501,896 km2 (193,783 sq mi), it is the largest desert in North America.

Alpine climate

Alpine climate is the typical weather (climate) for the regions above the tree line. This climate is also referred to as a mountain climate or highland climate.

Ecology of California

The ecology of California can be understood by dividing the state into a number of ecoregions, which contain distinct ecological communities of plants and animals in a contiguous region. The ecoregions of California can be grouped into four major groups: desert ecoregions, Mediterranean ecoregions, forested mountains, and coastal forests.

San Francisco Peaks

The San Francisco Peaks are a volcanic mountain range in San Francisco volcanic field in north central Arizona, just north of Flagstaff and a remnant of the former San Francisco Mountain. The highest summit in the range, Humphreys Peak, is the highest point in the state of Arizona at 12,633 feet (3,851 m) in elevation. The San Francisco Peaks are the remains of an eroded stratovolcano. An aquifer within the caldera supplies much of Flagstaff's water while the mountain itself is in the Coconino National Forest, a popular recreation site. The Arizona Snowbowl ski area is on the western slopes of Humphreys Peak, and has been the subject of major controversy involving several tribes and environmental groups.

Baja California Desert

The Baja California Desert is a desert ecoregion of Mexico's Baja California Peninsula. This ecoregion occupies the western portion of the Baja California peninsula, and occupies most of the Mexican states of Baja California Sur and Baja California. It covers 77,700 square kilometers. The climate is dry, but its proximity of the Pacific Ocean provides humidity and moderates the temperature. The flora mostly consists of xeric shrubs and over 500 species of recorded vascular plants.

Sierra de Juárez

The Sierra de Juárez, also known as the Sierra Juarez, is a mountain range located in Tecate Municipality and northern Ensenada Municipality, within northern Baja California state of northwestern Mexico.

Leslie Ransselaer Holdridge was an American botanist and climatologist. He was the father of composer Lee Holdridge.

Holdridge life zones Global bioclimatic scheme for the classification of land areas

The Holdridge life zones system is a global bioclimatic scheme for the classification of land areas. It was first published by Leslie Holdridge in 1947, and updated in 1967. It is a relatively simple system based on few empirical data, giving objective mapping criteria. A basic assumption of the system is that both soil and climax vegetation can be mapped once the climate is known.

Eastern Cascades Slopes and Foothills

The Eastern Cascades Slopes and Foothills ecoregion is a Level III ecoregion designated by the United States Environmental Protection Agency (EPA) in the U.S. states of Oregon, Washington, and California. In the rain shadow of the Cascade Range, the eastern side of the mountains experiences greater temperature extremes and receives less precipitation than the west side. Open forests of ponderosa pine and some lodgepole pine distinguish this region from the Cascades ecoregion, where hemlock and fir forests are more common, and from the lower, drier ecoregions to the east, where shrubs and grasslands are predominant. The vegetation is adapted to the prevailing dry, continental climate and frequent wildfire. Volcanic cones and buttes are common in much of the region.

Blue Mountains (ecoregion) Ecoregion (WWF)

The Blue Mountains ecoregion is a Level III ecoregion designated by the United States Environmental Protection Agency (EPA) in the Pacific Northwest, mainly in the state of Oregon, with small areas over the state border in Idaho and southeastern Washington. It is also contiguous with the World Wildlife Fund's Blue Mountain forests ecoregion.

Ecology of the North Cascades Ecosystems of the Cascade mountain range in northern Washington state and southern British Columbia

The Ecology of the North Cascades is heavily influenced by the high elevation and rain shadow effects of the mountain range. The North Cascades is a section of the Cascade Range from the South Fork of the Snoqualmie River in Washington, United States, to the confluence of the Thompson and Fraser Rivers in British Columbia, Canada, where the range is officially called the Cascade Mountains but is usually referred to as the Canadian Cascades. The North Cascades Ecoregion is a Level III ecoregion in the Commission for Environmental Cooperation's classification system.

Great Basin montane forests

The Great Basin montane forests is an ecoregion of the Temperate coniferous forests biome, as designated by the World Wildlife Fund (WWF).

Montane ecosystems

Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures fall as elevation increases, causing the ecosystem to stratify. This stratification is a crucial factor in shaping plant community, biodiversity, metabolic processes and ecosystem dynamics for montane ecosystems. Dense montane forests are common at moderate elevations, due to moderate temperatures and high rainfall. At higher elevations, the climate is harsher, with lower temperatures and higher winds, preventing the growth of trees and causing the plant community to transition to montane grasslands, shrublands or alpine tundra. Due to the unique climate conditions of montane ecosystems, they contain increased numbers of endemic species. Montane ecosystems also exhibit variation in ecosystem services, which include carbon storage and water supply.

Okanagan dry forests

Okanagan dry forests is a temperate coniferous forest ecoregion in the Pacific Northwest of North America, as defined by the World Wildlife Fund (WWF) categorization system. It is closely associated with the Okanagan region of British Columbia and Washington.

References

  1. McColl, R.W. (2005). Encyclopedia of World Geography. 1. Infobase Publishing. p. 961. ISBN   9780816072293.
  2. Ricketts, Taylor H.; Dinerstein, Eric; Olson, David M.; Loucks, Colby J.; et al. (1999). Terrestrial Ecoregions of North America: a Conservation Assessment. Washington DC: Island Press.
  3. "Ecological Regions of North America: Toward a Common Perspective" (PDF). Commission for Environmental Cooperation. 1997. Archived from the original (PDF) on 2004-01-04.
  4. "Holdridge's Life Zones". Geology class notes. Radford University. Archived from the original on 2008-01-10.