Dr Oliver Gilbert surveyed eight
lichens on the six best lichen sites in Breckland for English Nature last year.
He had previously surveyed them in 1991.
Starry breck-lichen Buellia asterella,
which once thrived in Breckland, has now completely died out in the UK.
Scrambled egg lichen Fulgensia fulgens,
which was once found across the area now
only struggles to survive in a few spots along the south and west coast of Britain,
Toninia
lobulata
has also gone from Breckland.
Four more species are now only found
in just two sites.
Rarities
Buellia asterella - Extinct,
Fulgensia fulgens - Extinct,
Squamarina lentigera - 4 localities down to 2,
Notable
Catapyrenium squamulosum - 6 localities down to 3
Diploschistes muscorum - 6
localities down to 3
Psora decipiens - 2 localities down to 1
Toninia lobulata - Extinct
Toninia sedifolia - 6 localities down to 3
The situation is even more critical as several species, though still present at a, site, have greatly reduced populations. At only two sites, RAF Barnham and Weeting Heath NNR, are the lichen communities still reasonably well developed and thought to have a future. The reason for the decline is that the formerly very open calcareous grassland has closed up. This is due to an expansion of the higher plants and even more to a luxuriant growth of pleurocarpous mosses, which have spread over the surface eliminating the network of bare mineral soil that formerly existed between the tufts of Festuca.
All the Breckland rare and notable species require a compact. highly calcareous mineral soil on which to grow and at many sites this niche has been eliminated. Aerial nitrogen inputs from industry / transport and agricultural sources are the most likely cause of sward closure. The formerly open Breckland grasslands dominated by Festuca ovina now contain mesotrophic species such as Agrostis capillaris,
Festuca rubra, Holcus lanatus and Trifolium repens which contribute
to a greatly increased biomass. In addition to a low nutrient status, grazing
is also required to maintain the short open turf required by the rarer lichens.
A mixture of rabbits and sheep has provided this, with the former preferred as
they graze more closely. Some ecologists regard sheep grazing as causing a
thickening up and closure of the sward so they could be responsible for the
rapid decline at one site.
Winter cattle grazing at Lakenheath Warren during
winter 2001/2002 turned the site into a sea of mud, and if Buellia asterella
had survived until then, its extinction would have been hastened. It is
significant that all localities and former localities for the Breckland
rarities, except for Lakenheath Warren, are man-made sites where the ground has
been disturbed, often to a considerable depth, bringing raw chalk soil to the
surface. The only management likely to be effective in reversing the fortunes
of the rare and notable lichens is to strip the soil from large areas to leave
bare chalk. These will then act as a ‘sticky fly-paper’ forming a habitat that
is receptive to the propagules of slow growing, stress tolerant species. The
new surface should be ideal for Toninia sedifolia that fruits
abundantly. Once this species has established it will form a framework among
which the other lichens will start to grow. It is unlikely that the three
extinct species Buellia asterella, Fulgensia fulgens and Toninia lobulata
will reappear but most of the rest should, including Squamarina lentigera
which is more dynamic than was previously thought.
The last eleven years have seen a dramatic contraction in the distribution of the three rare and five notable Breckland lichens. Between 1991 and 2002 three lichens have become extinct while the rest have been lost from half their former sites. The situation is even more critical as several species, though still present at a site, have greatly reduced populations. The cause of this decline is a result of the previouslyopen grassland having closed up due to the spread of higher plants and bryophytes denying the lichens the calcareous mineral soil they require as a substrate. After reviewing possible causes it is concluded that increased aerial inputs of nitrogen are chiefly responsible for sward closure. The only management that might help recovery of the remaining species is large scale, deep, soil stripping to initiate new primary successions. Grazing by rabbits is preferred; sheep are second best, and on no account should important lichen sites be exposed to cattle.
A copy of Dr Gilbert’s report, English Nature Research Report no
503 ‘Lichen survey of selected Breckland lichen sites 2002’ is available from:
English Nature, tel 01733 455101
or email enquiry.service@english-nature.org.uk
Nick Sibbett
© 2003 Suffolk Naturalists' Society