The concept of talus slopes co-evolving with vegetation cover is investigated on the Trotternish Ridge, Isle of Skye, Scotland. This uses several lines of contemporary and palaeoenvironmental evidence. Through a replicated set of grazing enclosures, the composition and structure of present-day vegetation is linked to contemporary grazing regimes and slope erosion processes. Vegetation history is reconstructed from the fossil pollen content of organic palaeosols intercalated within the talus deposits. A new method using Long Chain Alcohols is used to support the interpretation of the fossil pollen records. Geomorphological development is revealed through analysis of talus stratigraphy and the sedimentary deposits immediately below the slopes. These lines of evidence are combined to construct a conceptual model for talus co-evolution on the Trotternish Ridge. Talus development began as the climate warmed from around 17.5k cal yrs BP, and the glaciers of the last Ice Age retreated. Slopes initially comprised rockfall debris, with a sparse cover of vegetation having little or no effect on slope processes. Heathland and grassland vegetation, evidenced by the organic palaeosols, was intermittently present on the talus slope surfaces from 7.7-7.6k cal yr BP until approximately 0.6-0.5k cal yr BP. This vegetation cover limited physical and hydrological surface processes, enabling the upper part of the talus slopes to over-steepen. Evidence of increased frequency of organic palaeosol burial, and increased rates of sediment deposition after around 2.0k cal yr BP, both indicate greater debris flow and other erosional activity in the late Holocene. This is attributed to both increased incidence of intense rainfall events and much higher levels of grazing associated with the introduction of cattle, sheep and rabbits. Contemporary evidence shows that heavy grazing changes the vegetation composition and structure, and increases susceptibility to erosion. Talus co-evolution on the Trotternish Ridge may be similar to that at other British and Faroese sites which share the same basaltic geology.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:499308 |
| Date | January 2009 |
| Creators | Brown, Eleanor Clare |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=25969 |
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