Restless Earth and the Distribution of Life
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Restless Earth and the Distribution of Life The phrase 'Restless Earth' can be used to describe the constantly changing and evolving nature of this planet. When contemplating this phrase, one could consider the theory of plate tectonics as being the main theme within the concept of a restless earth. The phrase can also be interpreted in an ecological sense when considering the genesis of life on earth, its evolution and the global distribution of species. By studying areas of tectonic and volcanic activity; concepts that can be jointly considered; ecologists, geologists and geographers are able to garner an idea of how life first develops on newly formed land. The volcanic island of Surtsey, located in the ocean south of the Westman Islands off the coast of Iceland, built up out of the ocean following an eruption that started in 14 November 1963. The island now stands at 172m above sea level and has an area of approximately 2.5 sq.
A typical plant succession includes 5 major successive stages or seres leading up to a climax community and it is this kind of succession that can be applied when studying the ecological development on Surtsey. The five major stages in the succession as set out in Dickinson and Murphy (1998) are as follows: 1. Initiation - The starting point of a succession as a bare surface. Surtsey shortly following its formation provides an excellent example of this seral stage. 2. Colonisation - The stage at which highly specialised and stress-tolerant plants known as Colonisers begin to grow. 3. Development - Soil condition begins to improve and initial colonisers are replaced by more productive and competitive species such as grasses and weeds. 4. Mature - Vegetation cover is dominated by competitive species. Soil condition is stable, nutrient and water conditions are suitable for reasonable plant growth. 5. Climax - The final stage of a succession in which the vegetation cover is relatively stable and persistent.
Considering this information on an ecological scale, it would suggest that volcanic eruptions in this area play a prominent part in the formation of the ecosystems (Crisafulli and Hawkins, 1994). The 1980 eruption had a very visible impact on the surrounding area but had not completely destroyed all life in the 'blowdown zone'. The large trees that previously had intercepted most of the incoming light had been removed, meaning surviving saplings of smaller trees and plants were able to flourish because of the vastly decreased competition in the area. Also there were examples where succession had followed the classic ecological theory; wind-blown herbs, such as fireweeds had colonised the barren ash-covered surfaces of the blowdown zone. In some of the upland areas the recovering plant life was a mix of late-successional understorey and pioneering species. The ecosystems studied on Surtsey and in the Mount St. Helens area display how there can be differing responses to volcanic and tectonic events by successional flora and fauna. On Surtsey, a classic ecological succession can be observed which is in contrast to the mix of classic and recovering ecosystem succession in the Mount St. Helens area.
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