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The Arctic is an Ecosystem
by Bill Heal
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The Terrestial Ecosystem Or Ecosystems
Changes over time
  As the glaciers and ice caps retreated 10-20,000 years ago, the bare ground, shattered rock debris and boulder clay formed the initial 'soil'. On hard granite rocks weathering by the climate was slow, producing few coarse soil particles and little soluble nutrients. On limestone weathering was much faster and generated alkaline soils, but the particles dissolved quickly, drainage channels opened and nutrients tended to leach out of the system. On other sedimentary rocks, sand and clay particles were more abundant and essential nutrients such as phosphorus and potassium retained. The geology set the course of ecosystem development. Nitrogen was the missing element needed to start the plant succession. Input in rain was minimal, but blue-green algae with the ability to 'fix' atmospheric nitrogen grew where water was available. Some algae, using reflected light, even live under stones which efficiently absorb heat from the sun. Lichens grew slowly on rock surfaces. Made up of an alga and a fungus, lichens have the capacity to produce, decompose and recycle - a self-sufficient internal ecosystem.
  It is these early colonisers, with the capacity to capture essential nitrogen and nutrients from the racks, which initiate succession in places where there was no organic matter from previous systems - accumulation of nutrient capital is essential. Bacteria that can extract elements from the rocks - the chemolithotrophs - aid the process. As small amounts of organic matter accumulate, other plants begin to colonise by seed, the tiny amounts of organic material providing focal points for successful germination. In other areas where some organic matter remains from vegetation that preceded the ice cover or has been redistributed on river banks. Here, colonisation is more rapid, but is still often initiated by plants with associated nitrogen fixing bacteria.
  Early colonising plants tend to have a strategy of rapid growth and reproduction to take advantage of the sites that have colonised. Gradually other species come into the site, taking advantage of the protection of existing plants and the accumulated organic matter. Gradually the cover increases, moss cover increases and the ground becomes more insulated from the low temperatures. Ironically, this can cause the permafrost to thaw less, the active layer to become thinner giving more difficult rooting conditions, often waterlogging, and reduced recycling of nutrients. The plants that conserve their resources and recycle them internally to give them a kick-start at the beginning of summer, now tend to have the advantage. These are often the better competitors - what they have they hold. The gradual changes in plants and soil are followed by the fauna. The 'hotspots' of early colonising plants attract migrant grazers. Small insects are blown by the wind, the fortunate ones landing on the patches of vegetation. In the later stages, many of the plants are long-lived, woody and often produce 'defense' compounds that protect them against animals. The fauna then becomes more specialised and grazing is reduced to times when more palatable food is not available.
  The time scale of these dynamics, the primary succession, is measured in centuries and the sequence varies greatly from place to place, as do the initial conditions causing succession. Ground disturbance through freeze-thaw cycles, erosion, lake drainage, fire and Human activity such as trampling or industrial development, can all restart succession. Adjacent land with its vegetation and fauna, provides sources for colonisation. Thus the time scale of such secondary succession is often measured in decades.
  Fundamentally, the whole region has been subjected to variations in climate over thousands of years, sometimes warmer, sometimes cooler. The animals and plants have been selected to survive these changing, yet continually harsh conditions. They have adapted. Sophisticated adaptations, such as the use of anti-freeze chemicals, will enable them to respond and survive under the expected changes in climate caused by the carbon pumped into the atmosphere by Human activity. The distribution of species will change; some will move into new areas, others will withdraw; patterns will change - just as they always have done. The ebb and flow of varieties of reindeer around Greenland over the last 10,000 years illustrates these long-term dynamics. In this case caused by changes in land form, ice connections and glacial barriers, combined with climate, overgrazing, and predation by Man and wolves.
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The Arctic is an Ecosystem, by Bill Heal.
Copyright Stefansson Arctic Institute and individual authors ©2000
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