Resurvey of the Corticolous Lichen flora of Epping Forest
1981) of thalli sizes to determine approximate dates and suggested that colonisation by Parmelia
sulcata began early in the 1980s followed by Hypogymnia physodes some years later. However
our observations suggest a more complex situation in that developing thalli may be in a constant
state of growth fluctuation, with short dynamic growth and decay cycles often in response to small
short-term and local changes in their micro-environment thereby making such datings less reliable.
Overall in their conclusions sulphur dioxide and the loss of mature trees are cited as the most
important factors contributing to the demise of the lichen flora.
Table 1: Historical Records
Dates -No of Substrate Epiphytes Data Source
species only
Forster 1784-96 65 NHM (Crombie, 1885)
_____________________________________________________________Hawksworth & McManus (1991)
Crombie 1865-68 120 all 86 NHM
1881-82 86 all Hawksworth, Rose & Coppins
_____________________________________________________________(1973)__________________________
Paulson & 1909-19 129 all 49 Paulson & Thompson (1911,
Thompson___________________________________________________1913,1918,1920)__________________
Rose& 1969-70 28 Epiphytes 28 Hawksworth, Rose & Coppins
Pentecost____________________________________________________(1973)__________________________
Hawksworth & 1989-91 41 Epiphytes 41 Hawksworth & McManus (1991)
McManus___________________________________________________________________________________
Boreham 1987-91 6 Betula 6 Boreham (1993)
_______________________________________pendula_______________________________________________
Boreham (1993) recorded lichen flora on Betula pendula in northern Epping Forest from 1987 to
1991. He surveyed 170 trees of similar age (60-120 cm girth) in an area extending from the Wake
Arms, east of Piercing Hill, south to Birch Wood and Great Monk Wood and west to Wake Valley
Pond and Claypit Hill. He recorded on 10 trees per site at 17 locations. The annual mean percentage
cover of Lecanora conizaeoides fell from 58% to 25% over the period, but remained widespread
across the area. Cladonia coniocraea and Lepraria incana were also widespread, and despite an
increase in 1991, cover of the former did not significantly increase across the area unlike the latter,
which increased from 0.9% to 2.8%. Rare appearances of Lecanora chlarotera in 1990 and 1991
and L. expallens were recorded and Hypogymnia physodes was found on 14 trees at eight sites,
with the largest thalli in the central zones (>12mm) reducing towards the edge of the Forest to <
4mm.
Air Quality
Air quality has changed considerably since the beginning of the industrial revolution when lichen
records for Essex began. Emissions of sulphur dioxide, black smoke and other chemicals from
industrial activities in London increased over the period to the 1970s and urbanisation in
Walthamstow enhanced the impact of an already toxic cocktail of pollution across the Forest area.
Pollution, poor habitat management and urban sprawl reduced the lichen flora to little more than a
tenth of its original diversity. It was not until the Clean Air Act of 1956 that conditions began to
improve, with measures such as smokeless fuel and gas heating leading to a dramatic fall in sulphur
dioxide concentrations from an annual high of 136ppb (360 µgm3) recorded at County Hall (Fig. 1),
Essex Naturalist (New Series) 20 (2003)
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