@article {606, title = {Lichen Recolonization in London under Conditions of Rapidly Falling Sulfur-Dioxide Levels, and the Concept of Zone Skipping.}, journal = {Botanical Journal of the Linnean Society}, volume = {100}, year = {1989}, pages = {99-109}, author = {Hawksworth, D.L. and McManus, P.M.} }