Suprisingly, the air pollution sensitive Acrocordia gemmata was cited from three sites and Parmelia
perlata from four, but only small single specimens of the less sensitive Parmelia caperata, Physconia
distorta. Ramalina "calicaris", and Usnea "hirta" were mentioned. Thelotrema lepadinum was seen
only on a fallen Carpinus trunk east of Great Monk Wood — these were the last authors to see this
conspicuous lichen in the Forest.
Paulson is known to have been not entirely reliable in his identification of lichens (e.g. Laundon.
1967). and this consideration must be borne in mind when interpreting the lichen flora of the Forest
at this time from the published records. While a sounder impression could perhaps be derived from a
reexamination of their collections in EFM and PEM. contrary to some of Paulson & Thompson's
(1911, 1913) views, overall there appears to have been a definite further diminution in the lichen flora
by this time. Indeed. 36 species still present on trees in 1881-2 were not refound in 1909-26, including
Calicium viride, Caloplaca luteoalba, Candelaria concolor. Lecanactis premnea. Lecidella
elaeochroma. Ramalina farinacea. R fastigiata, and R. fraxinea. At the close of this period, most of
the Forest must have been of zones 4-5 of the Hawksworth & Rose (1970) scale, with species peculiar
to other zones occurring exceptionally in particularly sheltered spots. Paulson (1918) noted that any
increase in urban "smoke" would limit the extent to which the lichens in the Forest might become
more vigorous. Unfortunately, subsequent air pollution patterns meant that this was not to be the case.
1968-70
In the somewhat less comprehensive investigations carried out independently by Drs Pentecost and
Rose in this period. 28 lichen species were found on trees and wood (Hawksworth et al. 1973). Evernia
prunastri. Graphis elegans. Parmelia caperata, P. glabratula. P. perlata. Pertusaria amara and
Platismatia glauca were not discovered, and neither were any species of the genera Physcia.
Physconia. Ramalina. Usnea, or Xanthoria. The richest site studied during this period was Wintry
Wood which yielded, amongst other species. Enterographa crassa. Opegrapha atra. O. vulgata, three
Pertusaria species. Pyrrhospora quernea. Pyrenula chlorospila and Schismatomma decolorans. This
situation clearly continued into the mid-1970s: Rose, for example, in his rather widespread survey of
1974, found only three members of the Parmeliaceae (Hypogymnia physodes. Parmelia saxatilis, and
P. sulcata).
On the basis of direct field assessments, the southern parts of the Forest were referred to zone 3.
and the most northerly to zone 4 in 1968-70 (Hawksworth et al., 1973).
1989-91
Of the 41 species recorded on trees in 1989-91.21 (51 %) were not recorded in the period 1968-70.
The most recent findings include a number of conspicuous macrolichen species, notably Candelaria
concolor. Evernia prunastri. Foraminella ambigua, Hypogymnia tubulosa. Parmelia caperata, P.
perlata. P. revoluta. P. subaurifera. Phaeophyscia orbicularis. Physcia adscendens. P. tenella.
Platismatia glauca. Ramalina farinacea. Usnea subfloridana and Xanthoria parietina.
The sizes of the thalli of those species for which approximate growth rates are known, suggest that
the main period of recolonization has been since 1982-5 — well after the previous study.
However, 13 species found in 1968-70 were not refound by us in the present survey: Arthonia
spadicea. Buellia punctata. Diploicia canescens. Calicium salicinum. Cladonia chlorophaea.
Cliostomum griffithii. Graphis scripta, Lecanora chlarotera, Pyrrhospora quernea. Parmelia
saxatilis. Pertusaria hymenea. P. leioplaca. P. pertusa, and Pyrenula chlorospila. All of these species
were reported by Dr F. Rose, apparently from Wintry Wood. In 1991 the pollarded Carpinus trees
along Stump Ride in that wood still supported several rare species found by Dr Rose in 1970. including
Enterographa crassa, Opegrapha atra and O. vulgata, but they were restricted to two trees near the
main cross-rides within the Wood. The main north-south ride in particular had been recently subjected
to pollarding, thinning, and extensive clearance along its margins prior to our first visit to the Wood
in March 1991. The loss of the lichens found in 1970 may therefore have been due to a combination
of the removal of trees and disturbance of the light regimes. It will be of interest to see whether the
shade-requiring Enterographa crassa will be able to persist in this site.
Five species reported by various collectors in 1983-5 were also not seen by us on trees in 1989-91:
Cladonia chlorophaea. C. crispata var. cetrariaefbrmis. C. furcata, Dimerella pineti, and Trapeliopsis
gelatinosa. All but D. pineti are essentially soil-inhabiting, occasionally occurring on stumps and
tree-bases: the Dimerella is minute and probably overlooked.
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