The Holarctic ecozone
An ecozone is the broadest biogeographic division of the Earth's land surface, based on distributional patterns of terrestrial organisms.Ecozones delineate large areas of the Earth's surface within which organisms have been evolving in relative isolation over long periods of time, separated from...

 refers to the habitats found throughout the northern continents of the world as a whole. This region is divided into the Palearctic
The Palearctic or Palaearctic is one of the eight ecozones dividing the Earth's surface.Physically, the Palearctic is the largest ecozone...

, consisting of Northern Africa and all of Eurasia, with the exception of Southeast Asia and the Indian subcontinent, and the Nearctic
The Nearctic is one of the eight terrestrial ecozones dividing the Earth's land surface.The Nearctic ecozone covers most of North America, including Greenland and the highlands of Mexico...

, consisting of North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 north of southern 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...

. These are further subdivided into a variety of ecoregions. Many ecosystems, and the animal and plant communities that depend on them, are found across multiple continents in large portions of this ecozone
An ecozone is the broadest biogeographic division of the Earth's land surface, based on distributional patterns of terrestrial organisms.Ecozones delineate large areas of the Earth's surface within which organisms have been evolving in relative isolation over long periods of time, separated from...

. The continuity of these ecosystems results from the shared glacial history of this ecozone. The Floristic Boreal Kingdom
Boreal Kingdom
The Boreal Kingdom or Holarctic Kingdom is a floristic kingdom identified by botanist Ronald Good , which includes the temperate to Arctic portions of North America and Eurasia. Its flora is inherited from the ancient supercontinent of Laurasia...

 corresponds to the Holarctic ecozone.

Major ecosystems

Within the Holarctic ecozone, there are a variety of ecosystems. The type of ecosystem found in an area depends on the latitude and local geography. In the far north, a band of arctic tundra
In physical geography, tundra is a biome where the tree growth is hindered by low temperatures and short growing seasons. The term tundra comes through Russian тундра from the Kildin Sami word tūndâr "uplands," "treeless mountain tract." There are three types of tundra: Arctic tundra, alpine...

 circles the shore of the Arctic Ocean
Arctic Ocean
The Arctic Ocean, located in the Northern Hemisphere and mostly in the Arctic north polar region, is the smallest and shallowest of the world's five major oceanic divisions...

. The ground beneath this land is permafrost
In geology, permafrost, cryotic soil or permafrost soil is soil at or below the freezing point of water for two or more years. Ice is not always present, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of...

, frozen year-round. In these difficult growing conditions, few plants can survive. South of the tundra, the boreal forest stretches across North America and Eurasia. This land is characterized by coniferous trees. South of here, the ecosystems become more diverse. Some areas are covered in temperate grassland, while others are covered in temperate forest
Temperate forest
Temperate forests correspond to forest concentrations formed in the northern hemisphere. Main characteristics include: wide leaves, big and tall trees and non seasonal vegetation...

, dominated by deciduous trees. The southern extent of the Holarctic typically reaches into the desert
A desert is a landscape or region that receives an extremely low amount of precipitation, less than enough to support growth of most plants. Most deserts have an average annual precipitation of less than...

, which is dominated by plants and animals adapted to the dry conditions (Schultz 2007).

Species with a holarctic distribution

A variety of animal species are distributed across continents, throughout much of the Holarctic ecozone. Some of these included the brown bear, grey wolf, red fox, wolverine, moose, caribou, and common raven.

The brown bear
Brown Bear
The brown bear is a large bear distributed across much of northern Eurasia and North America. It can weigh from and its largest subspecies, the Kodiak Bear, rivals the polar bear as the largest member of the bear family and as the largest land-based predator.There are several recognized...

 (Ursus arctos) is found in mountainous and semi-open areas distributed throughout the Holarctic. It once occupied much larger areas, but has been driven out by human development and the resulting habitat fragmentation. Today it is only found in remaining wilderness areas.

The grey wolf (Canis lupus) is found in a wide variety of habitats from tundra to desert, with different populations adapted for each. Its historical distribution encompasses the vast majority of the Holarctic Ecozone, though human activities such as development and active extermination have extirpated the species from much of this range.

The red fox
Red Fox
The red fox is the largest of the true foxes, as well as being the most geographically spread member of the Carnivora, being distributed across the entire northern hemisphere from the Arctic Circle to North Africa, Central America, and the steppes of Asia...

 (Vulpes vulpes) is a highly adaptable predator. It has the widest distribution of any terrestrial carnivore, and is adapted to a wide range of habitats, including areas of intense human development. Like the wolf, it is distributed throughout the majority of the Holarctic, but it has avoided extirpation.

The wolverine
The wolverine, pronounced , Gulo gulo , also referred to as glutton, carcajou, skunk bear, or quickhatch, is the largest land-dwelling species of the family Mustelidae . It is a stocky and muscular carnivore, more closely resembling a small bear than other mustelids...

 (Gulo gulo) is a large member of the weasel family found primarily in the arctic and in boreal forests, ranging south in mountainous regions. It is distributed in such areas throughout Eurasia and North America.

The moose
The moose or Eurasian elk is the largest extant species in the deer family. Moose are distinguished by the palmate antlers of the males; other members of the family have antlers with a dendritic configuration...

 (Alces alces) is the largest member of the deer family. It is found throughout most of the boreal forest through continental Eurasia into Scandinavia, eastern North America, and boreal and montane regions of western North America. In some areas it ranges south into the deciduous forest.

The caribou, or reindeer
The reindeer , also known as the caribou in North America, is a deer from the Arctic and Subarctic, including both resident and migratory populations. While overall widespread and numerous, some of its subspecies are rare and one has already gone extinct.Reindeer vary considerably in color and size...

 (Rangifer tarandus) is found in boreal forest and tundra in the northern parts of the Holarctic. In Eurasia it has been domesticated. It is divided into several subspecies, which are adapted to different habitats and geographic areas.

The common raven
Common Raven
The Common Raven , also known as the Northern Raven, is a large, all-black passerine bird. Found across the northern hemisphere, it is the most widely distributed of all corvids...

 (Corvus corax) is the most widespread of the corvids, and one of the largest. It is found in a variety of habitats, but primarily wooded northern areas. It has been known to adapt well to areas of human activity. Their distribution also makes up most of the Holarctic Ecozone.


The continuity of the northern parts of the holarctic results from their shared glacial history. During the Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....

, these areas were subjected to repeated glaciations. Icecaps expanded, scouring the land of life and reshaping its topography. During glacial periods, species survived in refugia
In biology a refugium , sometimes termed simply a refuge, is a location of an isolated or relict population of a once more widespread species. This isolation can be due to climatic changes, geography, or human activities such as deforestation and over-hunting...

, small areas that maintained a suitable climate due to local geography. These areas are believed to have been primarily in southern regions, but some genetic and paleontological evidence points to additional refugia in the sheltered areas of the north (Stewart and Lister 2001).

Wherever these areas were found, they became a source populations during interglacial periods. When the glaciers receded, plants and animals spread rapidly into the newly opened areas. Different taxa responded differently to these rapidly changing conditions. Tree species spread outward from refugia during interglacial periods, but in varied patterns, with different trees dominating in different periods (Taberlet and Chedadi 2002). Insects, on the other hand, shifted their ranges with the climate, maintaining consistency in species for the most part throughout the period (Coope 1994). Their high degree of mobility allowed them to move as the glaciers advanced or retreated, maintaining a constant habitat despite the climatic oscillations. Despite their apparent lack of mobility, plants managed to colonize new areas rapidly as well. Studies of fossil pollen indicate that trees recolonized these lands at an exponential rate (Bennet 1986). Mammals recolonized at varying rates. Brown bears, for instance, moved quickly from refugia with the receding glaciers, becoming one of the first large mammals to recolonize the land (Sommer and Benecke 2005). The last glacial period ended about 10,000 years ago, resulting in the present distribution of ecoregions.

Another factor contributing to the continuity of Holarctic ecosystems is the movement between continents allowed by the Bering land bridge
Bering land bridge
The Bering land bridge was a land bridge roughly 1,000 miles wide at its greatest extent, which joined present-day Alaska and eastern Siberia at various times during the Pleistocene ice ages. Like most of Siberia and all of Manchuria, Beringia was not glaciated because snowfall was extremely light...

, which was exposed by the lowering of sea level due to the expansion of the ice caps. The communities found in the Palearctic and the Nearctic are different, but have many species in common. This is the result of several faunal interchanges that took place across the Bering land bridge. However, these migrations were mostly limited to large, cold-tolerant species (Rodriguez et al. 2006). Today it is mainly these species which are found throughout the ecozone.


As the Holarctic is an enormous area, it is subject to environmental problems of international scale. The primary threats throughout the region result from global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...

 and habitat fragmentation
Habitat fragmentation
Habitat fragmentation as the name implies, describes the emergence of discontinuities in an organism's preferred environment , causing population fragmentation...

. The former is of particular concern in the north, as these ecosystems are adapted to cold. The latter is more of a concern in the south, where development is prevalent.

Global warming is a threat to all the Earth's ecosystems, but it is a more immediate threat to those found in cold climates. The communities of species found at these latitudes are adapted to the cold, so any significant warming can upset the balance. For instance, insects struggle to survive the cold winters typical of the boreal forest. Many do not make it, especially in harsh winters. However, recently the winters have grown milder, which has had a drastic effect on the forest. Winter mortality of some insect species drastically decreased, allowing the population to build on itself in subsequent years. In some areas the effects have been severe. Spruce beetle outbreaks have wiped out up to ninety percent of the Kenai Peninsula
Kenai Peninsula
The Kenai Peninsula is a large peninsula jutting from the southern coast of Alaska in the United States. The name Kenai is probably derived from Kenayskaya, the Russian name for Cook Inlet, which borders the peninsula to the west.-Geography:...

's spruce trees; this is blamed primarily on a series of unusually warm years since 1987 (Logan et al. 2003).

In this case a native species has caused massive disturbance of habitat as a result of climate change. Warming temperatures may also allow pest species to enlarge their range, moving into habitats that were previously unsuitable. Studies of potential areas for outbreaks of bark beetle
Bark beetle
A bark beetle is one of approximately 220 genera with 6,000 species of beetles in the subfamily Scolytinae. Traditionally, this was considered a distinct family Scolytidae, but now it is understood that bark beetles are in fact very specialized members of the "true weevil" family...

s indicate that as the climate shifts, these beetles will expand to the north and to higher elevations than they have previously affected (Williams & Liebhold 2002). With warmer temperatures, insect infestation will become a greater problem throughout the northern parts of the Holarctic.

Another potential effect of global warming to norther ecosystems is the melting of permafrost
In geology, permafrost, cryotic soil or permafrost soil is soil at or below the freezing point of water for two or more years. Ice is not always present, as may be in the case of nonporous bedrock, but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of...

. This can have significant effects on the plant communities that are adapted to the frozen soil, and may also have implications for further climate change. As permafrost melts, any trees growing above it may die, and the land shifts from forest to peatland. In the far north, shrubs may later take over what was formerly tundra. The precise effect depends on whether the water that was locked up is able to drain off. In either case, the habitat will undergo a shift. Melting permafrost may also accelerate climate change in the future. Within the permafrost, vast quantities of carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 are locked up. If this soil melts, the carbon may be released into the air as either carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 or methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

. Both of these are greenhouse gas
Greenhouse gas
A greenhouse gas is a gas in an atmosphere that absorbs and emits radiation within the thermal infrared range. This process is the fundamental cause of the greenhouse effect. The primary greenhouse gases in the Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide, and ozone...

es (Stokstad 2004).

Habitat fragmentation threatens a wide variety of habitats throughout the world, and the Holoarctic is no exception. Fragmentation has a variety of negative effects on populations. As populations become cut off, their genetic diversity suffers and they become susceptible to sudden disasters and extinction. While the northern parts of the Holarctic represent some of the largest areas of wilderness left on Earth, the southern parts are in some places extensively developed. This ecozone contains most of the worlds developed countries, including the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 and the nations of Western Europe
Western Europe
Western Europe is a loose term for the collection of countries in the western most region of the European continents, though this definition is context-dependent and carries cultural and political connotations. One definition describes Western Europe as a geographic entity—the region lying in the...

. Temperate forests were the primary ecosystem in many of the most developed areas today. These lands are now used for intensive agriculture or have become urbanized. As lands have been developed for agricultural uses and human occupation, natural habitat has for the most part become limited to areas considered unsuitable for human use, such as slopes or rocky areas (Schultz 2007). This pattern of development limits the ability of animals, especially large ones, to migrate from place to place.

Large carnivores are particularly affected by habitat fragmentation. These mammals, such as brown bears and wolves, require large areas of land with relatively intact habitat to survive as individuals. Much larger areas are required to maintain a sustainable population. They may also serve as keystone species
Keystone species
A keystone species is a species that has a disproportionately large effect on its environment relative to its abundance. Such species play a critical role in maintaining the structure of an ecological community, affecting many other organisms in an ecosystem and helping to determine the types and...

, regulating the populations of the species they prey on. Thus, their conservation has direct implications for a wide range of species, and is difficult to accomplish politically due to the large size of the areas they need (Paquet 1996). With increasing development, these species in particular are at risk, which could have effects that carry down throughout the ecosystem.

Conservation actions

The threats to the Holarctic ecozone are not going unrecognized. Many efforts are being made to mitigate these threats, with the hope of preserving the biodiversity of the region. International agreements to combat global warming may help to lessen the effects of climate change on this region. Efforts are also underway to fight habitat fragmentation, both on local and regional scales.

The most comprehensive effort to combat global warming to date is the Kyoto Protocol
Kyoto Protocol
The Kyoto Protocol is a protocol to the United Nations Framework Convention on Climate Change , aimed at fighting global warming...

. Developed countries who sign this protocol agree to cut their collective greenhouse gas emissions by five percent since 1990 by sometime between 2008 and 2012. The vast majority of these nations are found within the Holarctic. Each country is given a target for emission levels, and they may trade emissions credits in a market-based system that includes developing countries as well. Once this period is ended, a new agreement will be written to further mitigate the effects of climate change. The process of drafting a new agreement has already begun. In late 2007, an international meeting in Bali
Bali is an Indonesian island located in the westernmost end of the Lesser Sunda Islands, lying between Java to the west and Lombok to the east...

 was held to begin planning for the successor to the Kyoto Protocol. This agreement will aim to build on the successes and failures of Kyoto to produce a more effective method of cutting greenhouse gas emissions (UNFCCC). If these efforts are successful, the biodiversity of the Holarctic and the rest of the world will see fewer effects of climate change.

Fighting habitat fragmentation is a major challenge in conserving the wide-ranging species of the Holarctic. Some efforts are limited to a local scale of protection, while others are regional in scope. Local efforts include creating reserves
Nature reserve
A nature reserve is a protected area of importance for wildlife, flora, fauna or features of geological or other special interest, which is reserved and managed for conservation and to provide special opportunities for study or research...

 and establishing safe routes for animals to cross roads and other human-made barriers. Regional efforts to combat habitat fragmentation take a broader scope.

One major such effort in the Holarctic is the Yellowstone to Yukon Conservation Initiative
Yellowstone to Yukon Conservation Initiative
The Yellowstone to Yukon Conservation Initiative or Y2Y is a joint Canada-US charitable organization that seeks to preserve and maintain the wildlife, native plants...

. This organization was started in 1997 to help establish a contiguous network of protection for the northern Rocky Mountains
Rocky Mountains
The Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States...

, from mid Wyoming
Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...

 to the border between Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...

 and Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

's Yukon
Yukon is the westernmost and smallest of Canada's three federal territories. It was named after the Yukon River. The word Yukon means "Great River" in Gwich’in....

. It brings together a wide variety of environmental organizations for a shared purpose. The goal of the Initiative is to create a core of protected areas, connected by corridors and surrounded by buffer zones. This will build on the many existing protected areas in this region, with a focus on integrating existing and future human activities into the conservation plan rather than seeking to exclude them (Yellowstone to Yukon). If these efforts are successful, they will be especially beneficial to wide-ranging species such as grizzly bear
Grizzly Bear
The grizzly bear , also known as the silvertip bear, the grizzly, or the North American brown bear, is a subspecies of brown bear that generally lives in the uplands of western North America...

s. If these species can survive, other members of the communities they live in will survive as well.
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