Cliffs, together with vegetated crevices, ledges and cliff-tops along the coasts of the Baltic Sea, the North Sea and the Atlantic Ocean south to middle Portugal. Exposed bedrock dominates the habitat, and its very variable composition and structure determine the character of available surfaces. The height and slope of the cliffs influence the input of salt spray which, on exposed coasts, can be very high close to the sea. This combination of local climatic and topographic conditions determines the often strong zonation of crevice vegetation, grasslands and heaths found on the cliffs, with regional climate also affecting the flora. Nesting seabirds also add a distinctive nutrient-demanding element to the flora on their guano.