Lichens, inc. Bunodophoron melanocarpum, & bryophytes in a South East oceanic microclimate. 22.05.23
Updated: Aug 3
I made a trip to Eridge Rocks in the High Weald, yesterday; it is one of my favourite sites in Sussex. This Sussex Wildlife Trust reserve is in the High Weald and has an oceanic microclimate. The sandrock bluffs, which are a gill feature where Ardingly Sandstone outcrops, are the main stronghold of oceanic bryophytes (mosses and liverworts) in the South East. (Bangs D. (2018). The Land of the Brighton Line. A field guide to the Middle Sussex and South East Surrey Weald.) I got to Eridge Rocks on the 29 bus from Brighton. I get off at the Eridge Green stop; the entrance to the reserve is a short walk down Warren Farm Lane just south of Eridge Green bus stop. 29 - Brighton-Tunbridge Wells | Brighton & Hove Buses The bus runs hourly and it take 90-105 minutes to get to Eridge Green from Brighton.
My previous posts on Eridge Rocks can be accessed here:
The photographs in this post are organised into categories rather than presented chronologically (order of sighting)
All sections of text in italics are quotations, sources sited.
I am only an amateur naturalist; thus all identifications are provisional; if you note a mistake in identification please feel free to tell me. If you want to contact me about any aspect of this blog, email me at simeon[underscore]elliott[at]gmail[dot]com.
I was prompted to visit Eridge Rocks on this occasion because I had just returned from visiting some temperate rain forests in Scotland (Dunollie Woods, Glen Nant and Glasdrum reserves; all in Argyle), and I wanted to review an area of oceanic woodland near home in the light of this experience.
Blog posts on these Scottish temperate rain forests can be accessed here:
Extract from the Reserve Profile (Sussex Wildlife Trust)
Hidden away from the busy A26, along a small lane in Eridge Green are the impressive sandstone outcrops of Eridge Rocks. These rocks are a distinctive feature of the High Weald, important in their own right as geological features, but also home to a suite of lower plants, including many rare mosses, liverworts and lichens. Surrounding the rocks is semi-natural ancient woodland, a mixture of Sweet Chestnut, Birch and Hazel with a good number of veteran Oak and Beech scattered throughout.
These sandstone rocks were probably formed in the last glacial period of the Ice Age 20 to 50,000 years ago, though the actual sand would have been deposited in a river system during the Cretaceous Period approximately 138 million years ago. They are characterised by large boulders and vertical joints which are widened through ongoing weathering and movement, some of which are now just about wide enough to squeeze through. The rocks themselves have developed a hardened crust which helps protect them from the weather and shows some characteristic types of weathering including strange small hollows known as honeycomb weathering and polygonal cracking on the rounded tops of the rocks. The base of the rocks is often undercut to form overhangs and rock shelters. Archaeological investigations of some of these rock shelters at Eridge produced many struck flints of Mesolithic date and even some late Iron Age/early Romano-British smelting. As these flints were small and not of local origin it is thought that raw flints were transported into the area and then made into tools and weapons, suggesting the rock shelters were used temporarily by a small group of mobile hunter gatherers as has been found in similar locations in the Weald.
Eridge Rocks is designated as a Site of Special Scientific Interest for its lower plant interest, the mosses, lichens and liverworts. Many are so called oceanic species – species normally associated with the mild oceanic climate of Western Britain rather than South East England, but are able to thrive here in the mild, damp semi-shaded environment that the rocks provide. One of the specialities of the rocks is the Tunbridge Filmy-fern, so named as it was first discovered on the High Rocks at Tunbridge Wells in the 17th century. It is found in just a couple of locations at Eridge Rocks but surveys in 2016 found that it had recently colonised a few new areas of the rock face. ...
The lichen Bunodophoron melanocarpum a species thought to have been lost to shade at Eridge, had survived and is now expanding. The liverwort Harpanthus scutatus which had not been seen at Eridge since 1952 was recorded from a single quadrat in 2004 and continues to spread. Some of the other specialities at Eridge Rocks include the lichen Cladonia caespiticia a rare species on rocks and is very rare in Sussex but present in at least three locations at Eridge; the mosses Dicranum scottianum and Orthodontium gracile, and the leafy liverwort Bazzania trilobata. Reserve profile | Sussex Wildlife Trust
Nature England SSSI Reasons for Notification
This area of ancient woodland lies on Grinstead clays with outcrops of Tunbridge Wells sandstone. The sandstone outcrops support an unusual flora. Eridge Green is shown as woodland on the 1st Edition Ordnance Survey map of 1816 and it is likely that woodland cover has been maintained since at least the Middle Ages. The majority of the wood, however, has been modified by broadleaved and conifer plantations and Rhododendron is widespread. The woodland canopy helps retain a microclimate of high humidity which favours the sandrock flora. The sandstone outcrops form a cliff face up to 10 metres high. The red or yellow sandstones have been weathered to a dark brown or black by re-deposited iron oxides. Notable species recorded from the rocks include the Tunbridge filmy fern Hymenophyllum tunbrigense, the mosses Dicranum scottianum arid Orthodontium gracile and the liverworts Scapania umbrosa, S. gracilis and Harpanthus scutatus. Only the woodland on steep slopes above the rocks is unmodified with mature beech Fagus sylvatica occurring with holly Ilex aquifolium and yew Taxus baccata above a sparse ground flora of bramble Rubus fruticosus. Elsewhere Rhododendron and planted sweet chestnut Castanea sativa and larch Larix decidua are fairly widespread amongst the indigenous pedunculate oak Quercus robur, hazel Corylus avellana, birch Betula pendula, ash Fraxinus excelsior, sycamore Acer pseudoplatanus and beech. Bluebells Hyacinthoides non-scripta and dog’s mercury Mercurialis perennis form a dense ground flora in places. The woodland rides support a flora which includes water-pepper Polygonum hydropiper and corn mint Mentha arvensis. A small stream runs through the site but is heavily shaded by trees and contains little vegetation. 1002853 (naturalengland.org.uk)
Features of Ghyll Woodlands
Eridge Rocks is in the High Weald and is a ghyll wood, although it's ghyll is small. Ghyll woodlands have an unusual micro-climate and they are therefore unique. The flora found in these sites is very characteristic of former Atlantic conditions - including lush growths of ferns (such as hay scented buckler fern), mosses and liverworts. Many are likely to be primary woodland sites (potentially dating from the ice-age) and some have received relatively little disturbance, pollution or management. Ghyll’s provide an important function within the wider river catchment. They help to capture and slow down rainfall and overland run-off which would otherwise have a high capacity for erosion in these steep areas. They also provide shade and protection from sunlight, which provides a kind of ‘thermostatic regulation’ to downstream areas of river by cooling down water temperatures. ... Over 6% of the High Weald in Sussex is classed as ‘Ghyll’ woodland. This rare habitat type is a unique landscape feature of this part of Sussex and of the UK. Ghyll woodland in these terms specifically applies to the woodland found in the Sandstone and Hastings beds of the High Weald. Wet woodland | Sussex Wildlife Trust
The sheltered valleys occupied by ghyll woodlands buffer temperature fluctuations and maintain high humidity levels resulting in unusually oceanic micro-climatic conditions (Rose 1995). Elsewhere in northwestern Europe, ghyll-like valleys are rare, and thus the concentration of these features in lowland England has international geomorphological and ecological significance (Rose and Patmore 1997) Burnside, Niall & Metcalfe, Daniel & Smith, Roger & Waite, Steve. (2006). Ghyll Woodlands of the Weald: Characterisation and Conservation. Biodiversity and Conservation. 15. 1319-1338. 10.1007/s10531-005-3875-5. (PDF) Ghyll Woodlands of the Weald: Characterisation and Conservation (researchgate.net)
Lichens on the rocks (saxicolous lichens)
I saw the lichen Bunodophoron melanocarpum at Eridge Rocks; which elsewhere in the UK is typically a lichen of Atlantic (western) temperate rain forests. The only records for this lichen outside the temperate rain forest zones of the UK are in the Weald. I have only seen this here and in Glen Nant National Nature Reserve in Argyll. It is infertile at Eridge Rocks. t is rarely fertile; fertile B. melanocarpum is characteristic of temperate rainforests.
Bunodophoron melanocarpum at Eridge Rocks
B. melanocarpums in Glen Nant (Argyle), a temperate rain forest; seen on tree, Sessile Oaks and Hazels, not rock
Fertile. The black apothecia gives it the vernacular name Black Eyed Susan
The distribution of B. melanocarpum typically maps the UK Temperate Rain Forest Zone, as mapped by Dr Chris Hills (see below).
From: Ellis, Christopher J. "Oceanic and temperate rainforest climates and their epiphyte indicators in Britain." Ecological Indicators 70 (2016): 125-133.
There are a number of Cladonia spp. growing on the Ardingly Sandstone. Cladonia species are very difficult to identify.
These Cladonia sp. are possibly infertile C. coniocraea or infertile C. caespiticia, are growing in a sticky fluid, possibly a colloid of minerals from the sandstone, and are relatively abundant on the rocks.
If this is C. caespiticia, it is another example of an Eridge Rocks (High Weald) species more typically found in west Welsh and Scottish Atlantic zones (temperate rain forest) although, it has been recorded on various other places in the UK
Habitat: On mossy tree trunks, stumps and earth banks chiefly in sheltered situations, often in long-established, mature woodlands; widespread but rather local, easily overlooked and often sterile, when it cannot be identified with confidence. Rare on sheltered banks in heathlands and shaded mossy rocks in woods. Cladonia caespiticia | The British Lichen Society (my underlining)
Possibly Cladonia polydactyla
Possibly Cladonia squamosa
I also saw Polypody ferns, probably Polypodium vulgare, growing on moss on the sandstone rocks. Polypody ferns, when epiphytes on trees, are characteristic of temperate rain forests. Polypody ferns at Eridge Rocks grow on a few of the rocks
An evergreen, perennial, rhizomatous fern of well-drained, predominantly acidic substrates, including dry-stone walls, roadside banks and rock outcrops. It also occurs as an epiphyte on oaks and other deciduous trees, mainly in western Britain and Ireland, and is also found in conifer plantations. It is very tolerant of exposure, growing, for example, on montane scree. 0–760 m (Beinn na Socaich, Westerness). Biogeography Suboceanic Temperate element. Polypodium interjectum Shivas in BSBI Online Plant Atlas 2020
Bryophytes on the rocks (saxicolous bryophytes)
I did not see any of the bryophytes mentioned in the SSSI specification but I did see:
Tetraphis pellucida (moss)
A Calypogeia probably C. fissa (liverwort)
with gemmae. Most liverworts can reproduce asexually by means of gemmae, which are disks of tissues produced by the gametophytic generation. The gemmae are held in special organs known as gemma cups and are dispersed by rainfall. Liverwort | plant | Britannica
Probably Isothecium myosuroides
Possibly Dicranum tauricum
Ground (terricolous) and bark (corticulous) bryophytes
There are many terricolous and corticulous bryophytes at the Eridge Rocks reserve. These weren't the focus of this visit, but this Polytrichastrum formosum, with its antheridia which holds the gametes, reproductive organs, where the sperm are located, captured my attention because of its beauty
Lichens on trees (corticulous lichens)
There are many corticulous lichens Eridge Rocks; but I did not focus on these this trip. I include just Thelotrema lepadinum and Flavoparmelia caperata here, as Thelotrema lepadinum; an indicator species of ancient woodlands; and Flavoparmelia caperata is ubiquitous
Looking like little barnacles growing on tree trunks, barnacle lichen is found mainly on the bark of living trees in ancient woods, and it is indicative of longstanding woodland conditions. Barnacle Lichen (Thelotrema lepadinum) - Woodland Trust
Trees and the geomorphology of the Eridge Sandstone
The geomorphology of the Ardingly sandstones Eridge Rocks is one of its most distinctive features. Yews, Hazels and Oaks which grow adventurously on the Ardingly sandstone rocks; seemingly defying the need for much soil! These tress are living adventurously.
Eridge Rocks to me is a landscape of myth - it's Sussex with a Celtic twist!