Restless Earth and the Distribution of Life

disrupted and altered all types of ecosystems within this area (Crisafulli and Hawkins, 1994).

Dealing firstly with the volcanic island of Surtsey, we encounter an island that can be viewed

as an ecological 'clean slate'; an area uncolonised by any biota and consisting solely of abiotic

matter. It has been by suggested Fridiksson (1975), along with his counterparts of the Surtsey

Research Society, that on the island they may have been the creation of biotic matter through

the process of abiogenesis. The research party using the seawater from the ocean

surrounding the island and molten lava collected from fissures present on the island conducted

several field experiments. The results of these experiments suggested that the super-heated

reaction between the nutrient-rich seawater and the molten lava had created several amino

acids, especially large traces of glycine and alanine. Using this evidence, it was further

suggested that abiogenesis was not solely confined to the primordial conditions of primitive

earth, but could in all possibility occur wherever conditions permit. Although these findings

may be used to argue the case for the origin of life on earth, it is not suggested that these were

the processes that molded the ecological development on the island of Surtsey.

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:

. 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. Long-living large trees may dominate the community. Often all initial

colonising species have disappeared.

The colonisation of biota on the island of Surtsey is a very incomparable succession due to the

isolated nature of the island. Plant species that have located on Surtsey have had to overcome

a greater barrier in order to reach the island. Due to the oceanic barrier the main ways of

plant dispersal to Surtsey are by air or ocean currents. Also plant seeds could possibly be

transported by migrating birds, however the most likely and most successful method of

dispersal has been noted to be by oceanic currents (Fridiksson, 1975)

Ten years after the formation of Surtsey, Fridiksson notes that there is hardly any

competition on the dry land of Surtsey between the newly invaded plants. This would

suggest that at this mentioned time the succession on the island is still in its colonising or first

seral stage. The island's vegetation consisted of mainly mosses growing on the lava flow and

small amount of small vascular plants. Fauna that existed on the island is limited to migratory

birds and insects who feed on seeds and diaspores washed ashore during stormy periods

(Fridiksson, 1975)

The study of the ecosystems within the blast zone of Mount St. Helens deals with a different

kind of succession from those mentioned on Surtsey. In the Mount St. Helens area, the

ecosystems in question are recovering ones and as a result, the successions located here do

not follow a typical model. Mount St. Helens has erupted more than 20 times in the last 4500

making the average space between eruptions 225 years. 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.

References

Dickinson, G. and Murphy, K. 1998. Ecosystems, Routledge, London.

Fridiksson, S. 1975. Surtsey: Evolution of Life on a Volcanic Island, Butterworths, London

Crisafulli, C.M. and Hawkins, C.P. 1994, Ecosystem Recovery Following a Catastrophic

Disturbance: Lessons Learned from Mount St. Helens, USGS, [WWW]

http://biology.usgs.gov/s+t/SNT/noframe/np105.htm (October 17th 2000)

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