Arctic ecology

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Arctic ecology is the scientific study of the relationships between biotic and abiotic factors in the arctic, the region north of theArctic Circle (66 33’). This is a region characterized by stressful conditions as a result of extreme cold, low precipitation, a limited growing season (50-90 days) and virtually no sunlight throughout the winter. The Arctic is comprised of taiga (or boreal forest) and tundra biomes, which also dominate very high elevations, even in the tropics. Sensitive ecosystems exist throughout the Arctic region, which are being impacted dramatically by anthropogenic climate change.

1 The Arctic Environment
2 Biomes
3 Tundra
4 Boreal
5 Adaptations to the Arctic
6 Plant Adaptations
7 Conservation and Environmental Issues
8 Works Cited

[edit] The Arctic Environment

To understand Arctic ecology, it is important to consider both the terrestrial and oceanic aspects of the region. A few important parts of this environment are sea ice and permafrost.

Sea ice is frozen seawater that moves with oceanic currents; it provides important habitat and a resting place for animals, particularly during the winter months. Over time, small pockets of salty seawater get trapped in the ice, and the salt is squeezed out. This causes the ice to become progressively less salty. Sea ice persists throughout the year, but there is less ice available during summer months.

Large portions of the land are also frozen during the year. Permafrost is substrate that has been frozen for a minimum of 2 years. There are two types of permafrost: discontinuous and continuous. Discontinuous permafrost is found in areas where the mean annual air temperature is only slightly below freezing (0°C); this forms in sheltered locations. In areas where the mean annual soil surface temperature is below -5°C, continuous permafrost forms. This is not limited to sheltered areas and ranges from a few inches below the surface to over 1,000 feet deep. The top layer is called the active layer. It thaws in the summer and is critical to plant life.

[edit] Biomes

Moisture and temperature are major physical drivers of natural ecosystems. The more arid and colder conditions found at higher northern latitudes (and high elevations elsewhere) support tundra and boreal forests. The water in this region is generally frozen and evaporation rates are very low. Species diversity, nutrient availability, precipitation, and average temperatures increase as you move from the tundra to boreal forests and then to deciduous temperate ecosystems, which are found south of these Arctic biomes.

[edit] Tundra

Tundra is found from 55 ° to 70° N latitude in North America, Eurasia and Greenland. It can be found at lower latitudes at high elevations as well. The average temperature is -56°C; during the summer it is less than 10°C. Average precipitation ranges from 10 to 50 cm, and the permafrost is 400-600m thick. Plant species supported by tundra have small leaves, are short (74 mm to <5 m), tend to be deciduous, have a high ratio of roots to shoots, and are composed mainly of perennial forbs, dwarf shrubs, grasses, lichens, and mosses.

[edit] Boreal

In comparison to tundra, boreal forest supports in species diversity, an increase in canopy height, vegetation density, and biomass. Boreal conditions can be found across northern North America and Eurasia. The short (3-4 month) growing season in boreal forests is sustained by greater levels of rainfall (between 30 and 85 cm per year) than the tundra receives; This biome is dominated by closed canopy forests of evergreen conifers, especially spruces, fir, pine and tamarack with some diffuse-porous hardwoods. Shrubs, herbs, ferns, mosses, and lichens are also important species. Stand-replacing crown fires are very important to this biome, occurring as frequently as every 50-100 years in some parts.

[edit] Adaptations to the Arctic

The barren Arctic tundra is full of life in the Arctic summer. Many animals, including mammals, insects and birds migrate to the tundra from lower latitudes. Animals that are active in the winter have adaptations for surviving the intense cold. A common example is the presence of strikingly large feet in proportion to body weight. These act like snowshoes, and can be found on animals like the snowshoe hare and caribou. Many of the animals in the Arctic are larger than their temperate counterparts (Bergmann’s rule), taking advantage of the smaller ratio of surface area to volume that comes with increasing size. This increases the ability to conserve heat. Layers of fat, plumage, and fur are also very effective insulators to help retain warmth and are common in Arctic animals including polar bears and marine mammals. Some animals also have digestive adaptations to improve their ability to digest woody plants either with or without the aid of microbial organisms. This is highly advantageous during the winter months when most soft vegetation is beneath the snow pack.

Not all Arctic animals directly face the rigors of winter. Many migrate to warmer climates, while others avoid the difficulties of winter by hibernating until spring. Although these options might seem to be easy solutions to the diffictulties of surviving an extreme environment, both are very expensive in terms of energy and risk of predation.

Humans living in the Arctic region generally rely on warm clothing and buildings to protect them from the elements. Acclimatization, or the adjustment to new conditions, appears to be the most common form of adaptation to cold environments. No genetic advantage has been found when different people groups or races are compared. There is no evidence that fat is grown in response to cold, although its presence is advantageous. Amazingly, most people living in the Arctic region live a lifestyle very connected to the environment, spending significant time outside and depending heavily on hunting and fishing.

[edit] Plant Adaptations

One of the most serious problems that plants face is ice crystal formation in the cells. This results in tissue death. Plants have two ways to resist freezing: avoid it or tolerate it. If a plant chooses the avoidance route, it has several different ways to evade freezing. It can build up insulation, have its stem close to the ground, use the insulation from snow cover, and supercool. When supercooling, water is able to remain in its liquid state down to -38°C (compared to its usual 0°C freezing point). After water reaches -38°C, it spontaneously freezes and plant tissue is destroyed. This is called the nucleation point. The nucleation point can be lowered if dissolved solutes are present.

If a plant chooses the tolerance route, it has several different ways to tolerate freezing. Some plants allow freezing by allowing extracellular, but not intracellular freezing. Plants let water freeze in extracellular spaces, which creates a high vapor deficit that pulls water vapor out of the cell. This process dehydrates the cell and allows it to survive temperatures well below -38°C.

Another problem associated with extreme cold is cavitation. Ring-porous wood is susceptible to cavitation because the large pores that are used for water transport easily freeze. Cavitation is much less of problem in trees with ring-diffuse wood. In ring-diffuse wood, there is a reduced risk of cavitation, as transport pores are smaller. The trade-off is that these species are not able to transport water as efficiently.

[edit] Conservation and Environmental Issues

Worldwide anthropogenic climate change has been particularly evident in the Arctic. This is evident by warmer temperatures, melting glaciers, shorter durations of sea ice and changing weather and storm patterns. Scientists are especially concerned about four aspects of the continued projected warming of the Arctic.

First, thermohaline circulation is a series of underwater oceanic currents fueled by the salinity and temperature of seawater. Melting ice sheets would introduce vast amounts of fresh water into the North Atlantic, causing a change in density which could disrupt the currents. If this circulation slowed or stopped, the climates of northern Europe and North America would be strongly impacted.

Second, the melting of glaciers and sea ice is disrupting the lifestyles of a wide range of species. Polar bears live on the sea ice for much of the year and find their food in the surrounding ocean waters. Recent projections suggest that global warming will lead to the disappearance of most summer sea ice within 40 years.

A third practical concern is the melting of permafrost due to climate change. Degradation of this permafrost is leading to major ground surface subsidence and pounding. The ground is literally melting away in many regions of the Arctic. The locations of towns and communities that have been inhabited for centuries are now in jeopardy. A condition known as drunken tree syndrome is being caused by this melting. Ground water and river runoffs are being negatively impacted as well. Although warming conditions might increase CO₂ uptake for photosynthetic organisms in some places, scientists are concerned that melting permafrost will also release large amounts of carbon locked in permafrost.

Finally, the impacts of the release of carbon from the permafrost could be amplified by high levels of deforestation in the Boreal forests in Eurasia and Canada. This biome currently serves as a large carbon sink, sequestering large amounts of carbon dioxide. However, over half of the original forest has been or in danger of harvesting, largely for export. Carbon Dioxide is a greenhouse gas, which facilitates increased warming of the earth.