Salinity on chalk cliffs and its influence on maritime vegetation

The chalk cliffs of south-eastern England are liable to catastrophic cliff falls, giving edaphic conditions very variable in space and time. Chalk has ∼50% porosity, holding much water between 100 kPa and 1,000 kPa, but its availability to plants is restricted by salinity. The electrical conductivity of extracts of saturated pastes (ECs), as commonly used for agricultural soils, was used to measure the salinity of chalk and chalky soils. Studies along cliff transects between Folkestone and Dover showed that salinity thus measured was a good predictor of the distribution of both individual plant species and associations. Cliff geomorphology was far more important than distance from the sea in explaining salinity and plant distribution. We suggest that moist chalk surfaces are effectively impermeable, causing salt spray to run off during storms and concentrate in crevices, ledges and the topmost part of talus slopes, even at 400 m from the sea, which then support halophytes. We suggest that ECs could be used to model the interaction of salinity and competitive vigour.