Resurvey of the Corticolous Lichen flora of Epping Forest
Discussion
The earliest records of Forster and Crombie give an indication of the diversity and special nature of
the Forest even though they are not necessarily complete. The species recorded also give a good
indication of the contemporary community structure and target significant species occurring at a
particular period in time. Records are available for Epping Forest since 1784 and a comparative
review of current species shows that species numbers, whilst similar to those published by Forster,
reflect a very different flora to that of two centuries earlier. The diversity recorded by Crombie, as
with Forster's records, indicates the presence then of a typical ancient woodland lichen flora that
requires a continuity of tree cover over a very long period and which has subsequently been totally
destroyed by sulphur dioxide resulting in this particular lichen community being almost certainly
lost forever. Present diversity exceeds the lowest records from the 1970s (28 species) and more
recently the 41 species (Hawksworth & McManus 1992) recorded across the whole site. These two
more recent surveys both recorded highest diversity in the north (Wintry Wood). Conversely,
according to our survey, Wintry Wood now has the lowest diversity with 35 species. In contrast the
most southerly site with 42 species has seen a five-fold increase in diversity since the 6 to 8 species
recorded between 1970 and 1991 and exceeds the 1991 total for the Forest. It is the site closest to
London. Importantly, community structure varied considerably across all sites with the less common
species mostly confined to the more sheltered central parts of the Forest.
Of the total species recorded seventeen (more than a quarter) are new to Epping Forest. Of these
Bacidia delicata, Xanthoria polycarpa, Lecanora symmicta, L. confusa, Rinodina gennarii,
Mycoblastus fucatus, Flavoparmelia soredians, Candelariella reflexa and Buellia griseovirens
were recorded at all four sites. Physcia aipolia is now widely distributed in the London area and
has increased in frequency across England in the past decade. Conversely Chrysothrix flavovirens,
generally found on the drier side of trees in the cast and southern parts of Britain and Caloplaca
flavocitrina (formerly within the Caloplaca citrina complex) are becoming more widespread.
Gyalideopsis anastomosans is not uncommon, although easily overlooked, and Micarea peliocarpa
is infrequent in London.
The normally saxicolous Lecanora muralis, also a new record, was found on the base of an Oak in
the car park area of Great Monk Wood. All sites surveyed had a typical 'urban' flora at car parks
and major picnic areas, and such species were more frequent and abundant at site 4, closest to
London. The most common species in this community are: Amandinea punctata, Phaeophyscia
orbicularis, Physcia adscendens, P. tenella, Xanthoria parietina, X. candelaria, and X. polycarpa.
All have been recorded in the Forest since 1784 with the exception of Xanthoria polycarpa and
Physcia, adscendens. Physcia adscendens was first recorded in the 1989 to 91 survey; Xanthoria
polycarpa has increased significantly across England in recent years and is now abundant on London
tree boles and twigs. This species was once considered an indicator of low acidification. Other
typical urban species arc: Bacidia delicata, Candelariella reflexa, Flavoparmelia caperata, F
soredians, Lecanora confusa, L. symmicta, Punctelia subrudecta and Physcia, aipolia. These species
were not generally found in the more dense areas of the Forest except on the ridge towards the top
of Woodridden Hill at site 2.
Lecanora conizaeoides, which previously was the dominant species across all sites under high
sulphur dioxide levels, has largely disappeared from trunks with the exception of those sites closest
to London at Walthamstow where it formed a good cover on old Oaks. It was however noted as still
common on twigs and branches at most sites.
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Essex Naturalist (New Series) 20 (2003)