Coastal habitats throughout the world offer opportunities for plant survival that do not exist in the more competitive sites of inland areas. In the polar regions coasts in areas that were not permanently covered by snow and ice during the Pleistocene provided refugia for plant survival north of the ice sheets. It is the coastal areas today that still provide a viable habitat for relict species from the circumterrestrial Tertiary forests. Shore habitats are almost the last remaining habitats that allow plants to migrate without impediment from human interference. Littoral plant communities, due to their ability to migrate between similar habitats, also provide some of the best sites for monitoring the effects of climatic change, particularly when they have a north-south geographic orientation. Coastal sites may be marginal, and the dangers of physical destruction may be great, but the resilience of the plants to accommodate themselves to change has ensured their survival in the past and hopefully will continue to do so in the future.

Fig. 8.1 Plants inhabiting the water's edge at varying depths of inundation in a shallow loch in north-west Sutherland, Scotland. Common reed (Phragmites australis) in the shallows and white water lilies (Nymphaea alba) in the deeper water.

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