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The influence of various ecological factors on the distribution of gortigolous lichens, in Horsley Hope ravine, near Consett, Co. Durham

Wright, D. C. (1976) The influence of various ecological factors on the distribution of gortigolous lichens, in Horsley Hope ravine, near Consett, Co. Durham. Masters thesis, Durham University.

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Rose, Hawksworth and Coppins 77recorded a rich, corticolous lichen flora from Horsley Hope Ravine, despite its position just S.W. of Consett - a major source of S02-pollution. This study attempts to explain the apparently anomalous presence of a luxuriant lichen vegetation in the ravine. Three possible explanations were considered:1. Prevailing winds transport S02 N.E., so that the entire area S.W. of Consett, including the ravine, is relatively unpolluted. 2. The ravine is protected from S02-pollution by its physiographical shape and/or woodland cover. 3. The variations of certain abiotic factors within the ravine account for its diverse lichen flora. Records of corticolous lichen frequency in the area indicate that: (a) the lichen vegetation is impoverished S.W. of Consett, and (b) the E. sides of trees (exposed to S02-laden winds) support a poorer lichen flora than the W. sides. It is thus concluded that the distribution of lichens S.W. of Consett is affected by S02-impaction, so that explanation 1. may be discounted. Measurements of S02, and other doiotic factors, showed that S02-concentrations, light intensities and substrate moisture-content varied significantly within Horsley Hope Ravine. Transects down the sides of the ravine revealed two distinct patterns of lichen distribution: (i) the variation in frequencies of species downslope, (ii) the consistent, preference of species for the upper or lower sides of trees. Pattern (i) was correlated with downslope changes in S02-levels and light; pattern (ii) was explained by variations of S02, light, and substrate moisture-content. Species similarly distributed according to these two patterns were grouped into four lichen units. A model was developed which showed that the luxuriant lichen flora, and distribution of these four units, in Horsley Hope Ravine may be explained by (in order of importance): reduced levels of S02, variations in light intensity, and substrate moisture-content. The decline in S02-levels in the ravine was ascribed to topographical shelter from S02-bearing winds.

Item Type:Thesis (Masters)
Award:Master of Science
Thesis Date:1976
Copyright:Copyright of this thesis is held by the author
Deposited On:14 Mar 2014 16:04

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