Salt-Spray Deposition on the Maritime Cliffs of the Lizard Peninsula

Abstract

A survey of the cliff vegetation of the Lizard and Land's End Peninsulas of Cornwall suggested that deposition of salt-spray may play an important part in determining the composition and distribution of the vegetation types. Maritime species are more abundant on the west coast of the Lizard Peninsula, which is exposed to the prevailing westerly winds (dominant direction west-south-west), than on the east coast, while trees and shrubs show the opposite pattern. The relative effects of wind and salt* are difficult to separate; the damage to the windward side of trees and shrubs could be due to either wind or salt, or to a combination of both. An increase in wind speed can cause a failure to gain height and dry weight of a plant, possibly by increasing the saturation deficit until photosynthesis becomes negligible (Whitehead 1957). Boyce (1954) considers that, after entry through mechanical damage, the chloride ion is rapidly translocated to the apices of leaves and twigs of dune plants, accumulating there in injurious quantities, whereas chloride is not carried to the leeward side of the plant in injurious quantities. Parsons & Gill (1968) found that severe leaf-tip necrosis and death of shoots on the seaward side of bushes were common, and that an increased chloride content is detectable on the seaward side of bushes compared with the inland side. They conclude that the close association of dead shoots and leaves showing chloride toxicity symptoms with high chloride content suggests that chloride toxicity is the cause of asymmetric growth of exposed coastal shrubs. The studies mentioned above are largely concerned with the content of chloride ions within the plant, and little attention has been paid to the absolute values of salt deposition in a cliff ecosystem and the relation to the vegetation types present. The Lizard Peninsula provides a good site for an investigation of the variation of salt deposition with distance from the sea, since it is a fairly level platform of about 90 m altitude with few trees or topographical features likely to influence air movement greatly and thus the deposition of salt. The salt deposition in several cliff vegetation types in the Lizard Peninsula was also studied.