Wind damage in British forests of Sitka spruce has been considered a serious commercial constraint and research has sought to predict and prevent such losses. However, developments in forest policy have reduced the focus on timber production. Not all stands are to be managed to economic rotations. Some stands are to be left in perpetuity to provide structural and biological diversity; others are being given extended rotations or managed by silvicultural systems that do not involve clearfelling. I consider that wind could become the determinant of stand structure, rather than simply an agent of damage, and in some cases lead to self-perpetuating stands of Sitka spruce through spontaneous regeneration. To examine the potential for self-perpetuation, I studied the frequency of strong winds in upland Britain, and examined the processes of gap formation, expansion and filling of Sitka spruce stands. Britain has an extreme wind climate, comparable with a few maritime locations in temperate areas of the World. This implies the need for caution in transference of results from elsewhere. Gaps of a range of size, including those apparently suitable for spruce regeneration, form during periods of very strong winds. In intervening periods, there is a slow expansion of gaps by attrition at the edges, but this does not produce the largest gaps found within stands. Gap filling is occurring through lateral closure of small gaps, and by seedling regeneration and epicormic sprouting within larger gaps. The mechanism of epicormic sprouting from fallen trees has not been emphasised in literature from the Pacific North West, and bears some resemblance to recovery of forests in hurricane-prone areas. A case study of one of the oldest stands of Sitka spruce in upland Britain, Birkley Wood, showed that the components can come together to produce a self-perpetuating stand. Gap area has increased from 4 to 30% over 16 years. The tallest regeneration has now reached 8 m height, close to cone-bearing size, and meeting one of the accepted definitions of gap filling. The results have practical application in the development of alternatives to clear-felling, the selection of spruce areas as 'natural reserves', and in the treatment on Britain's wind climate in models of windthrow risk.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:660841 |
| Date | January 2001 |
| Creators | Quine, Christopher P. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/12819 |
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