Discussion
The lichen record in Epping Forest over the last 200 years reflects both increasing loss of continuity
of mature trees, and increasing and then decreasing sulphur dioxide levels. Changes due to the latter
are summarized in Table 2. The estimates of falling sulphur dioxide levels based on the lichen data
in the period since 1968 conform to the pattern of the physical measurements of gaseous sulphur
dioxide made at the recording station in Hoe Street, Walthamstow (51/374887; Warren Spring
Laboratory, 1969-88), the nearest site to the Forest with almost continuous readings through this
period. In 1967/8 the mean winter sulphur dioxide level there was 206 gm-3, a decade later in 1977/8
it was 111 gm-3, but by 1986/7 (the last year for which published records are available) had fallen to
37 g itt . A dramatic fall in the sulphur dioxide levels correlates with a remarkable resurgence in the
lichen flora in recent years.
Species characteristic of old forests require a continuity of mature trees to persist in a site have
gradually been lost throughout the last two centuries. Lobaria pulmonaria had disappeared before
1865, and Thelotrema lepadinum was last seen on a fallen tree sometime between 1912 and 1919.
Pyrenula chlorospila was last seen in 1974 by Dr F. Rose in the Lodge Road bog area, but was
"moribund or dead". The only "old forest" lichen remaining in 1991 was Enterographa crassa — now
apparently confined to two recently pollarded and unhealthy Carpinus trees on Stump Road in Wintry
Wood.
While only 41 (28 %) of the 145 species recorded on trees in the Forest over the last 200 years were
found in 1989-91, that number represents an increase of 13 (32%) since 1968-70. If the current
much-reduced sulphur dioxide levels are maintained, a continuing improvement of the lichen flora of
the Forest is to be expected. We may expect the lichen communities to gradually equilibrate at about
zone 8 of the Hawksworth & Rose (1970) scale, but without species which also require the continuity
of mature trees. As in the case of the Greater London area, crustose lichens particularly appear to be
slow to reestablish and more of these can be expected in due course.
In comparison to the lichen recolonization now documented as taking place in north-west London
(Hawksworth & McManus, 1989), the state of the lichen flora of Epping Forest was disappointing in
view of the 30 km distance of its northerly parts from Charing Cross in central London. Of the 41
species found in Epping, all but eight were found in the north-west London study, which extended at
its maximum to 29 km from Charing Cross. However, 17 species recolonizing on trees in the London
survey were not detected at all in the Epping study. The relatively poor improvements in the Epping
Forest lichen flora may be restricted by the pattern of the prevailing winds. However, in both areas
the main recolomzation of foliose lichens appears to have started about the same time, involves "zone
skipping" (i.e. no build-up of zone 5-6 species), and correlates with rapidly falling local sulphur
dioxide levels.
In the present study we have not investigated lichens on rocky substrata (including buildings, walls,
kerbs, concrete posts, asbestos-cement, pavements, and churchyards), nor those on the ground within
the woodlands or in the remaining grassland and heathy areas. Paulson (1918) provides lists for two
heathland sites, Jack's Hill and Woodredon Hill, which merit a comparative investigation. At the
former site Cladonia portentosa (Dufour) Coem. was present in 1985 (K.J. Adams), although not
listed by Paulson. However, there appear to be no recent records of Coelocaulon aculeatum (Schreber)
Link, nor of any species of the genera Baeomyces and Peltigera. Investigations of the past and present
floras of these habitats will have to await future students of the Forest's lichens.
Acknowledgements
We are indebted to Mr J.I. Besent (Superintendent, Epping Forest) for permission to collect
specimens in the Forest for identification purposes', to Mr P. Moxey (Field Studies Council) for advice
about promising collecting sites and access to records in the centre's care: and to Dr A. Pentecost. Dr
B.J. Coppins, Dr F. Rose, Professor M.R.D. Seaward, and Mr J.F. Skinner for making their records
available to us. Mr M.W. Hanson (Essex Field Club) is also thanked for his helpful comments on the
first draft of this contribution.
References
Crombie, J.M. (1870) Lichenes Britannici. London: Reeve.
Crombie, J.M. (1885) On the lichen-flora of Epping Forest, and the causes affecting its diminution. Transactions ami Proceedings of the Essex
Field Club 4: 54-75.
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