The Holarctic is the name for the biogeographic realm that encompasses the majority of habitats found throughout the northern continents of the world, combining Wallace's Palearctic zoogeographical region, consisting of North Africa and all of Eurasia (with the exception of the southern Arabian Peninsula, Southeast Asia, and the Indian subcontinent), and the Nearctic zoogeographical region, consisting of North America, north of Mexico. These regions 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 realm. The continuity of these ecosystems results from the shared glacial history of the realm. The floristicBoreal Kingdom corresponds to the Holarctic realm.
Within the Holarctic realm, 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 circles the shore of the Arctic Ocean. The ground beneath this land is permafrost, 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, dominated by deciduous trees. The southern extent of the Holarctic typically reaches into the desert, 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 realm. These include the brown bear, grey wolf, red fox, wolverine, moose, caribou, golden eagle and common raven.
The brown bear (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 realm, though human activities such as development and active extermination have extirpated the species from much of this range.
The red fox (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 (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 (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 (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 golden eagle (Aquila chrysaetos) is one of the best-known birds of prey in the Northern Hemisphere. It is the most widely distributed species of eagle. Golden eagles use their agility and speed combined with powerful feet and massive, sharp talons to snatch up a variety of prey (mainly hares, rabbits, marmots and other ground squirrels).
The common raven (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 realm.
Leptothorax acervorum is a small red holarctic ant widely distributed across Eurasia, ranging from central Spain and Italy to the northernmost parts of Scandinavia and Siberia.
Origin
The continuity of the northern parts of the holarctic results from their shared glacial history. During the Pleistocene, 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, 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 source populations during interglacial periods. When the glaciers receded, plants and animals spread rapidly into the newly opened areas. Different taxa responded to these rapidly changing conditions in different ways. 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, 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 realm.
Threats
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 and habitat fragmentation.[citation needed] 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'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 beetles 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. 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 are locked up. If this soil melts, the carbon may be released into the air as either carbon dioxide or methane. Both of these are greenhouse gases (Stokstad 2004).
Habitat fragmentation threatens a wide variety of habitats throughout the world, and the Holarctic 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 realm contains most of the worlds developed countries, including the United States and the nations of Western Europe. 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, 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 realm 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. 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 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 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. This organization was started in 1997 to help establish a contiguous network of protection for the northern Rocky Mountains, from mid Wyoming to the border between Alaska and Canada's Yukon. 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 bears. If these species can survive, other members of the communities they live in will survive as well.
Related Research Articles
A biome is a community 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.
In physical geography, tundra is a type of biome where the tree growth is hindered by low temperatures and short growing seasons. The term tundra comes through Russian тундра from the Kildin Sámi word тӯндар meaning "uplands", "treeless mountain tract". Tundra vegetation is composed of dwarf shrubs, sedges and grasses, mosses, and lichens. Scattered trees grow in some tundra regions. The ecotone between the tundra and the forest is known as the tree line or timberline. The tundra soil is rich in nitrogen and phosphorus.
Taiga, generally referred to in North America as boreal forest or snow forest, is a biome characterized by coniferous forests consisting mostly of pines, spruces, and larches.
The Nearctic is one of the eight biogeographic realms constituting the Earth's land surface.
The Palearctic or Palaearctic is one of the eight biogeographic realms of the Earth. It was first used in the 19th century, and is still in use as the basis for zoogeographic classification. The Palearctic is the largest of the eight realms. It stretches across all of Eurasia north of the foothills of the Himalayas, and North Africa.
In biology, a refugium is a location which supports an isolated or relict population of a once more widespread species. This isolation (allopatry) can be due to climatic changes, geography, or human activities such as deforestation and overhunting.
In paleoclimatology of the Holocene, the Boreal was the first of the Blytt-Sernander sequence of north European climatic phases that were originally based on the study of Danish peat bogs, named for Axel Blytt and Rutger Sernander, who first established the sequence. In peat bog sediments, the Boreal is also recognized by its characteristic pollen zone. It was preceded by the Younger Dryas, the last cold snap of the Pleistocene, and followed by the Atlantic, a warmer and moister period than our most recent climate. The Boreal, transitional between the two periods, varied a great deal, at times having within it climates like today's.
The California Floristic Province (CFP) is a floristic province with a Mediterranean-type climate located on the Pacific Coast of North America with a distinctive flora similar to other regions with a winter rainfall and summer drought climate like the Mediterranean Basin. This biodiversity hotspot is known for being the home of the Sierran giant sequoia tree and its close relative the coast redwood. In 1996, the Province was designated as a biodiversity hotspot allowing it to join ranks among 33 other areas in the world with many endemic species. To be named a biodiversity hotspot, an area has to contain species and plant life that cannot be found anywhere else in the world. The California Floristic Province is home to over 3,000 species of vascular plants, 60% of which are endemic to the province.
A boreal ecosystem is an ecosystem with a subarctic climate located in the Northern Hemisphere, approximately between 50° to 70°N latitude. These ecosystems are located in Boreal forests which are commonly known as the taiga, particularly in Europe and Asia. The ecosystems that lie immediately to the south of boreal zones are often called hemiboreal.
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The fauna of Europe is all the animals living in Europe and its surrounding seas and islands. Since there is no natural biogeographic boundary in the east and south between Europe and Asia, the term "fauna of Europe" is somewhat elusive. Europe is the western part of the Palearctic ecozone. Lying within the temperate region, the wildlife is not as rich as in the hottest regions, but is nevertheless diverse due to the variety of habitats and the faunal richness of Eurasia as a whole.
Ecotourism in the United States is commonly practiced in protected areas such as national parks and nature reserves. The principles and behaviors of ecotourism are slowly becoming more widespread in the United States; for example, hotels in some regions strive to be more sustainable.
A drought refuge is a site that provides permanent fresh water or moist conditions for plants and animals, acting as a refuge habitat when surrounding areas are affected by drought and allowing ecosystems and core species populations to survive until the drought breaks. Drought refuges are important for conserving ecosystems in places where the effects of climatic variability are exacerbated by human activities.
Arctostaphylos rubra is a species of flowering plant in the heath family and the genus Arctostaphylos, the manzanitas and bearberries. Common names include red fruit bearberry, alpine bearberry, arctic bearberry, red manzanita, and ravenberry. It is native to Eurasia and northern North America from Alaska through most of Canada to Greenland. There is also one population in the contiguous United States, located in the Absaroka Mountains of Wyoming.
The effects of climate change in Saskatchewan are now being observed in parts of the province. There is evidence of reduction of biomass in Saskatchewan's boreal forests that is linked by researchers to drought-related water stress stemming from global warming, most likely caused by greenhouse gas emissions. While studies, as early as 1988 have shown that climate change will affect agriculture, whether the effects can be mitigated through adaptations of cultivars, or crops, is less clear. Resiliency of ecosystems may decline with large changes in temperature. The provincial government has responded to the threat of climate change by introducing a plan to reduce carbon emissions, "The Saskatchewan Energy and Climate Change Plan", in June 2007.
The Hudson Plains Ecoregion is a vast, flat, and waterlogged landscape. This ecoregion covers a 369,000 square kilometer area along the south shoreline of the Hudson Bay, which includes the Canadian provinces of Eastern Quebec, Northern Ontario and Western Manitoba. Because of the location of the ecoregion, winter prevails for many months of the year and rising temperatures, along with melting ice, makes fog common. The short summers provide a home for thousands of migrating birds. The region is used by humans for its mineral resources and hydroelectric power as a result of the abundance of water and emergent societal needs. Though relatively uninhabited and undisturbed, the natural resources of the Hudson Plains are still subject to anthropogenic activities. Its climatic, geographic, and evolutionary patterns categorize it as one of many ecoregions in North America.
The Canadian Arctic tundra is a biogeographic designation for Northern Canada's terrain generally lying north of the tree line or boreal forest, that corresponds with the Scandinavian Alpine tundra to the east and the Siberian Arctic tundra to the west inside the circumpolar tundra belt of the Northern Hemisphere.
Changing climate conditions are amplified in polar regions and northern high-latitude areas are projected to warm at twice the rate of the global average. These modifications result in ecosystem interactions and feedbacks that can augment or mitigate climatic changes. These interactions may have been important through the large climate fluctuations since the glacial period. Therefore it is useful to review the past dynamics of vegetation and climate to place recent observed changes in the Arctic into context. This article focuses on northern Alaska where there has been much research on this theme.
The Ecological regions of Quebec are regions with specific types of vegetation and climates as defined by the Quebec Ministry of Forests, Wildlife and Parks. Given the size of this huge province, there is wide variation from the temperate deciduous forests of the southwest to the arctic tundra of the extreme north.
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