boughs. Where present on such trees, the recolonizing parmeliaceous lichens were generally restricted
to basal buttress roots and horizontal or inclined younger branches.
The meaningful assignment of lichen communities on trees to the zones of the Hawksworth & Rose
(1970) scale is difficult in periods of ameliorating sulphur dioxide levels while the lengthy
re-colonization and equilibration to the changed conditions are in progress. Zone 4 communities still
persist in many areas, but species referrable to much higher zones are establishing in more sheltered
and(or) northerly parts of the Forest. Notably species referrable to zones 6 (Parmelia caperata). 1
(Candelaria concolor, P. revoluta. Usnea subfloridana), and 8 (P. perlata).
Changes In The Lichen Flora
1784-96
In the late eighteenth century, as evidenced by Forster's records. Epping Forest had a rich lichen
flora comparable to that of parklands and forests in many rural areas of southern England today. It
then included a wide variety of species now known to be sensitive to sulphur dioxide air pollution
(e.g. Physconia distorta, Ramalina fraxinea. Usnea hirta) and others which require a continuity of
old trees to persist (e.g. Lecanactis lyncea. Lobaria pulmonaria, Thelotrema lepadinum). The species
present suggest that communities of zones 9-10 of the qualitative scale of Hawksworth & Rose (1970)
were then present. Additional evidence for the richness of the lichen flora in the district at this time
derives from Forster's discovery of further pollution-sensitive species in Hainault Forest, notably
Bryoria fuscescens (Gyelnik) Brodo & D.Hawksw.. Caloplaca cerina (Ehrh. ex Hedwig) Th.Fr..
Pertusaria coccodes (Ach.) Nyl. and Usnea ceratina Ach.
1865-68
In his detailed analysis of the lichen flora almost exactly 100 years after Forster's investigations.
Crombie (1885) noted that in the lichen flora as a whole, of the 171 species he accepted, 46 discovered
by Forster had not been refound. Those lost included both species sensitive to disturbance in woodland
continuity and ones now recognized as air pollution sensitive, for example Anaptychia ciliaris, Biatora
sphaeroides, Lobaria pulmonaria, Parmelia acetabulum, Usnea cornuta, and U. glabrata. Indeed no
Usnea species were found by Crombie, and neither did he record Parmelia perlata (P. caperata was.
however, present then) or refind Platismatia glauca.
These observations, taken together with the occurence of Anisomeridium biforme. Graphis elegans,
Rinodina roboris, and a variety of Pertusaria, Physcia, and Ramalina species, indicates that the lichen
communities had deteriorated to at best zone 7 of the Hawskworth & Rose (1970) pollution sensitivity
scale by the late 1860s.
1881-82
Crombie (1885) stated that 40 of the lichens he had personally recorded from all habitats in 1865-8
had been lost by 1881-2. Amongst the 22 species occurring on trees not refound after this 17-year
interval were Graphis elegans. Hyperphyscia adglutinata. Lecanactis lyncea, Lecanora pallida,
Pertusaria flavida, Physcia tenella. Physconia distorta. Phlyctis agelaea, and Rinodina roboris.
Further, he noted a reduction in the frequency and vigour of a variety of species which had not been
eliminated entirely, including Enterographa crassa. Evernia prunastri. Micarea denigrata,
Phaeographis dendritica, and Pyrenula macrospora. Parmelia caperata. Ramalina farinacea, and
various other Ramalina and also Pertusaria species were still present, but Hypogymnia physodes and
Parmelia saxatilis were evidently not frequent; somewhat surprisingly. P. sulcata was indicated as
"not observed".
Crombie's data indicates that by the early 1880s the lichen flora over much of the Forest had
deteriorated to at most zone 5 on the Hawksworth & Rose (1970) pollution scale, with some areas in
the centre and north reaching zone 6. Thelotrema lepadinum was evidently still present at High Beach
and in Wintry Wood. The continuing decline in the lichens of the Forest since Forster's time was
attributed by Crombie to a combination of three factors; the destruction of older trees, the dense
crowding of the trees leading to low light intensities, and the encroachment of "villages" accentuated
by prevailing winds bring "smokes and fogs of London" into the Forest.
1909-26
Paulson and Thompson (1911, 1913. 1920) recorded 49 species on trees during this period. They
considered that, since Crombie's studies, Hypogymnia physodes and Parmelia saxatilis (probably
including P. sulcata) had become more abundant in response to clearance work in the Forest.
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