THE LICHEN VEGETATION OF ACID WATERCOURSES IN ENGLAND

The lichen vegetation of ferry-five acid watercourses in England is de scribed and related to ecological variables. The zonation scheme adopt ed for chalk and limestone streams that involves four overlapping band s of lichen vegetation related to length of submergence is also approp riate for this habitat. The flora involves around 90 species, a number of which are rarely recorded specialists. Evidence is presented that substratum chemistry is a more powerful ecological factor than water c hemistry. An attempt has been made to relate the lichen flora to homog eneous stream segments from the headwaters down to the alluvial lowlan ds. An investigation into the effects of water quality showed that bot h suspended solids (silting) and eutrophication are highly deleterious to the lichen flora; the submerged and fluvial mesic zones are the fi rst to be affected. The zonation across streams in England is compared with those reported from Germany and found to be closely similar. (C) 1997 The British Lichen Society.