- Types of seashore habitat
- Management guidelines for seashore lichen communities
1.1 Lichens can be a considerable but often overlooked component of maritime nature reserves. Such communities occur on or near to seashores throughout the world, from warm-temperate to arctic regions. Types of seashore lichen communities in Britain and Northern Europe are reasonably well-known and are reviewed in Fletcher (1980). They can be found on rock, soil, tree bark, lignum and man-made substrata such as seawalls. Consequently, any habitat on or near the seashore may be expected to bear lichens. It is important to note that though these organisms can be inconspicuous, they may attain 100% cover on apparently bare seashore rock. A preliminary listing of important coastal sites was prepared by James and Wolseley (1990).
1.2 Seashores may be declared as National Nature Reserves, and/or scheduled as SSSIs. They can also be managed by conservation agencies as local nature reserves, or as Local Authority conservation areas, perhaps by way of seeking to improve a beach for amenity purposes. But although such reserves are managed, and often intensively so, it is rare for lichens to be given consideration in management plans. Only Fletcher (1996) can be cited, where a brief summary of lichen habitat management intentions on Bardsey Island was given. Therefore, it is should be remembered that most of the proposals made below are tentative. Ideally they should be treated as guidelines, be implemented with an experimental attitude, and the results monitored. Eventually, with the benefits of experience, firmer advice should evolve.
1.3 The purpose of this paper is to provide guidelines for those managing seashore nature reserves in the British Isles. It outlines where seashore lichens might be found, then highlights threats to which seashore lichens are especially sensitive and about which site managers must be aware. Finally, some ideas and proposals are suggested by which lichens might be integrated into a general management plan, ensuring that these organisms are preserved and encouraged.
2. Types of Seashore Habitat.
2.1 Rocky shores. These have been intensively studied in the UK (Fletcher 1972, 1973a,b, 1975a,b, 1976) and the subject reviewed (Fletcher 1980). Here, a descriptive community classification was devised integrating rocky shore lichen community patterns with those of other seashore organisms, as outlined by Lewis (1962). Briefly, the scheme runs as follows;
- Eulittoral zone Lowest limits of tides, few lichens are found here in the UK except Lichina pygmaea and Pyrenocollema spp.
- Littoral zone The 'intertidal zone', bears species of Verrucaria and Pyrenocollema. It will be completely above high tide levels on wave-exposed shores. Most apparently bare rock will be found to be occupied by lichens if examined with a lens.
- Littoral fringe The uppermost limit of Verrucaria maura, accompanied by Lichina confinis in shelter.
- Mesic supralittoral Dominated by orange Caloplaca marina on sunny shores and by grey Lecanora helicopis on shaded shores.
- Submesic supralittoral Dominated by orange Xanthoria parietina, the lowest limit of foliose species.
- Xeric supralittoral Dominated by saltwater dependent lichens, Ramalina siliquosa, Parmelia pulla, Anaptychia runcinata and many others, the most drought-prone part of the seashore.
- Terrestrial halophilic Home to saltwater tolerant lichens such as Parmelia caperata and Ramalina subfarinacea. Often extending to 1km or more inland on exposed cliffs.
- Terrestrial halophobic Dominated by species intolerant of seawater, the true terrestrial community to be expected inland.
2.1.1 Both calcareous and siliceous rocks have similar lichen communities in the eulittoral to submesic supralittoral, but on calcareous rock the supralittoral flora lacks any specifically maritime species (Fletcher 1972, 1986,1994). Instead, lichens typical of inland limestone predominate. It appears that seawater overcomes the effects of calcium ions in the littoral.
2.1.2 Important communities are found beneath overhangs and in crevices, especially on siliceous rocky shores. Many lichens at the northernmost limits of their geographical range are restricted to these habitats. These communities have been described by James (1970).
2.2 Maritime Soil. Most seashore rocks are overhung by soil, which also penetrates down-shore in crevices. A rich and often characteristically maritime lichen flora can be found here, frequently extending to culms of grasses, Thymus, Sedum anglicum, etc. Usually this flora is encouraged by grazing and wind-burn. Examples of species are Trapeliopsis wallrothii, Toninia mesoidea, Psora lurida and Moelleropsis nebulosa. Cladonia species are common here, especially C.foliacea on sunny shores, C. cervicornis, C. rangiformis and C. ciliata var. tenuis, with C. pocillum and C. subrangiformis on calcareous soil or shell sand. Sheltered shores have more acidic soils due to lesser amounts of sea spray. Here the Cladonia flora becomes one typical of more acid soils and may be dominated by C. pyxidata, C. chlorophaea, C. fimbriata and C. furcata.
2.2.1 An important lichen community occurs on soil on windswept cliff edges. Here can be found the scarce Teloschistes flavicans, Heterodermia leucomelos (both protected under the Wildlife and Countryside Act, Annex 8), Heterodermia obscunata, Rinodina roboris var. armeriicola (non R. subgfaucescens) and many others. It is possible that these species, mostly at the northernmost limits of their range on shores on the west coast of Britain, are dependent on wind-borne humidity. This community is species-rich and also includes Parmelia, Physcia and Cladonia spp.
2.3 Machair. This habitat, occurring in NW Scotland supports an unusual lichen community where wind-blown shell sand overlies rocks. Here, compacted soil, often dominated by blue-green algae, may have Solorina saccata and S. spongiosa, Collema and Leptogium spp. The very inconspicuous species of Thefocarpon may also occur. This environment is under threat from agricultural practices (Rose & Coppins 1983). Fletcher et al. (1984) evaluated lichen-rich machair sites as part of a lowland heathland evaluation.
2.4 Dunes. Dune lichens have received little attention since the pioneer works of McLean (1915), Watson (1918) and Alvin (1960). Lichens occupy characteristic zones depending on the dune's age, size and soil pH. The most widely dune-habitat classification system classifies dunes into two, with a mobile yellow -, and a stable, grey-dune phase. Mobile dunes lack lichens, being dominated by Marram Grass. Grey dunes are mostly dominated by Cladonia species, with C. foliacea, C. pocillum and C. rangiformis on the younger, most base-rich soils. Base-loving crustose species can also be found, including the rare Fulgensia fulgens, and Dipfoschistes muscorum, a parasite of Cfadonia pocilium. As the soils become more acid, away from the sea, a dune heath flora develops, ultimately being associated with Cafluna vulgaris and including the 'Reindeer Lichens' Cladonia ciliata var. tenuis, C. portentosa and C. rangiformis (Cladonia section Cladina lichens), with C. chlorophaea, C. pyxidata and C. furcata with Coelocaulon aculeatum, Bryoria fuscescens, Peltigera spp., and crustose species of Bacidia, Micarea and Vezdaea. Of especial interest in sheltered dune slacks, are lichens found freely blowing about on the soil (aegrophilous). These include Evernia prunastri, Ramalina farinacea, Usnea spp., and even Parmelia sulcata and P. caperata. These aegrophilous species may have originated on nearby trees or rocks. More recent articles include Topham & Hitch (1985) for Tentsmuir, Fife, while Fletcher et aL (1984) listed British lichen-rich dune sites as part of a lowland heathland evaluation.
2.5 Shingle. Shingle beaches occupy extensive stretches of the British coastline particularly in eastern England where rocky shores are scarce. These sites were reviewed by Fletcher (1984). The best examples are in NE Scotland such as Culbin, Ferry Links and Couthill Links, but Dorset (Chesil Beach, Watson 1922), Norfolk (Blakeney,) and Kent (Dungeness, see Laundon 1983) also have important examples. Lichens here are typically those of rocky shores, exhibiting a similar zonation pattern. However, the unstable habitat, where stones may be overturned by wave and wind action, discourages long-lived communities. On sheltered shingle in estuaries, a specialised marine community including Pyrenocollema orustensis, Verrucaria ditmarsica and V. erichsenii occur. These may be on stones so frequently overturned that lichens can occupy both upper and lower surfaces. Where shingle beaches have stabilised or become consolidated by sand, a rich dune or dune heath flora can develop, with rocky shore species on exposed pebbles. An overall review of shingle lichens is by Lambley and Hodgetts (2001).
2.6 Seawalls. Man-made substrata bear the same lichens as on rocky shores. However, the communities can be complex when calcareous ions from cement are present. A zonation typical of siliceous rocky shores may be found on the rocks, while calcareous floras similar to those occurring terrestrially are found in cement-filled crevices.
2.7 Saltmarshes. Timber of man-made origin, exposed on piles and jetties bears a confusing assortment of lichens of uncertain taxonomy. This may be because of the brackish nature of the water which encourages salt-tolerant terrestrial lichens rather than salt-dependent species.
Nearer the sea, Verrucaria maura can occupy a littoral zone on worked timber, while Caloplaca marina and Lecanora helicopis are found higher up. However, the supralittoral zone quickly gives way to iignicolous lichens such as Lecanora confusa, L. saligna and Cliostomum griffithii, with maritime elements such as Ramalina siliquosa. The rare Cliostomum graniforme is restricted to this habitat on saltmarshes. Hard woody stems of phanerogams often bear corticolous lichens not specific to the seashore.
2.8 Trees. Seashores are not an expected habitat for trees, yet coastal Prunus spinosa, Rhamnus catharticus, Calluna vulgaris and most others in shelter will bear coastal communities. Few of these lichens are specifically maritime however, and may best be considered seaspray tolerant, like their hosts. Rich and luxuriant communities can include Ramalina farinacea, R. fastigiata, Usnea spp., Evernia prunastri, Parmelia spp., etc.
2.9 Shells. A small but specialized lichen community exists on littoral seashelis, especially Barnacles (Balanus and Chthamalus spp.) and Limpets (Patella spp.). Many species live within the shell surface (endolithic), visible only by the black dots of their fruiting bodies. Examples include Pyrenocollema halodytes and P. sublitoralis. Some Verrucaria species, especially V. ditmarsica and V. halizoa can also occur here. Bones also bear calcareous lichens, often on dunes.
2.10 Ornithocoprophilous lichens form an important component of seashore rock communities. Some of the UK's scarcest lichens may be found here, including Ramaiina polymorpha, Buellia (Rinodina) orvulariopsis, Aspicila leprosescens, and others.
2.11 Miscellaneous substrata. Finally it should be mentioned that virtually any substratum of reasonable age can bear seashore lichens, for example, boot leather, carpet, polystyrene foam, abandoned cars and wrecked boats.
3. Management Guidelines for Seashore Lichen Communities.
3.1 Maritime nature reserves would be expected to include several of the abovecommunities. Many these communities are subject to the same threats, of trampling for example. Therefore, the management guidelines proposed below are arranged according to the commonest threats. The guidelines are best regarded as a checklist which could be accommodated within a management plan. Unfortunately threats to seashore lichens are rarely acknowledged. Marine lichens are often cited as being vulnerable to oil spills, but published support for this view is scarce. A rough assessment of known threats and their potential importance is given below
3.2 Natural succession. Lichen communities change in space and time. For example, monitoring studies since 1967 (Fletcher and Jones 1975, Fletcher 1976, and unpublished), suggest that littoral communities of Verrucaria, Pyrenocollema and Lichina are quite stable and changes in them are mostly due to growth, competition and grazing. Supralittorai communities however, can be very unstable and populations of foliose species such as Xanthoria parietina and Parmelia spp., may grow to maturity and be swept away within 5-10 years by wind and wave action. Therefore, since population fluctuations may be a natural process, they are beyond the scope of management. Much of this natural succession can be probably related to climate, especially seasonal fluctuations. Long term effects of climate change on seashore lichens remain to be analysed, though much data exists in photographic form, some as early as 1967 (Fletcher unpubl., Wolseley unpubl.).Dune systems show considerable changes in vegetation cover with time (Ketner-Oostra 1992, Topham and Hitch 1985), Veer and Koojiman 1997), Vestergaard and Alstrup 1996).
3.3 Grazing. Grazing is a natural agent causing change, especially by littoral animals such as limpets and winkles, or by snails, slugs, mites, etc in the supralittoral. The type of animal influencing lichens can often be detected from Limpet - radula or other marks. Indirect grazing occurs when birds investigate the undersides of foliose thalli for sheltering larvae and insects. Rock Pipits (Anthus petrosus) seem chiefly responsible for this on rocky shores. Grazing becomes a management issue when it is by animals introduced or favoured by man. However, none can be cited as particularly significant on the rocky seashore as grazing chiefly affects higher plants. Trampling though, may be highly damaging (see below). While the harmful effects of grazing should be considered, there is also a positive side in that it can be used to control scrub development. Therefore, management plans should attempt to control grazing by monitoring its effects quantitatively. But this is difficult to do at present until sufficient experimental management experience is available. Rabbits (Oryctolagus cuniculus) are an important factor in keeping turf short and encouraging cliff-top terricolous communities.>
3.3.1 Cladonia and Teloschistes flavicans, appear to depend, at least in part, on Rabbit activities which fragment and disperse the thalli. While high Rabbit populations can clear vegetation to bare soil, lichens seem to persist as fragments around Uiex or in rock crevices, eventually colonizing along with vascular plants when the Rabbit population declines through disease. Rabbit dung is also an important substratum for scarce lichens such as Rinodina conradii.
3.3.2 Rabbits compete with grazing animals such as sheep, so if the latter is used as a management tool, then contribution to grazing intensity of local rabbit populations must be calculated.
3.4 Shading and scrub development. Heavy, seasonal shading by seaweed temporarily obscures littoral lichens but appears to do no permanent harm. However, heavy new colonization by permanent holdfasts, or by crustose algae, reduce the substratum available. Scrub development is a serious threat to supralittoral seashore lichens. Succession can be held in check naturally by wind and wave action or by wild animal grazing. Of the controlling factors, probably only grazing can be influenced effectively by management plans. However, scrub development may also be promoted by erection of seawalls for sheltering a shore or dunes. Overgrowth by higher plants of any substratum, whether they be rocks, soil or trees, causes shading or excessive humidity which will oust the lichens if it is for a prolonged period. Plants responsible include potentially all higher plants when their natural grazing animals are removed, for example Rabbits. However, myxomatosis outbreaks make Rabbit population fluctuations a more or less natural phenomenon. Plants causing most concern however, include Bracken (Pteridium aquilinum), especially on dunes, and Gorse ((//ex sp.j, Blackthorn (Prunus spinosa) and Elder (Sambucus nigei) on rocky shores. Bracken is probably the least threat as it shelters rocks in summer and dies down in winter, exposing lichens to light during their growing season. However, leaf litter build up and humus deposits bury the rock surface. This is a problem caused by all vascular plants near to rocks. There may be cause for concern in the recent spread of garden shrubs onto maritime cliffs. Examples include Cotoneaster, Carpobrotus and Rhamnus catharticus. Therefore, a programme of 'mowing' near to critical rocks in the autumn may be in order. Gorse is more serious when on the shallow soils which predominate near rocks, as its shading is permanent. Fire should be avoided as a control measure because of the physical scorching of rock surfaces. Also, ash deposits affect saxicolous lichens by liberating nutrients and altering environmental chemistry by making it more base-rich. It also encourages Foxglove (Digitalis), an important shading agent.
3.5 The most satisfactory method for controlling scrub is probably grazing, provided the simultaneous effects of trampling and manuring are taken into consideration. Failing that, manual cutting, scything or mowing should be done. It is acknowledged however, that it may be impractical to manage scrub on sheltered rocky shores, so natural grazing agents such as Rabbits should be encouraged. The overhanging tops of sea cliffs should be regularly cleared of Gorse and Blackthorn to encourage maritime soil species and to prevent acidification of seepage which simplifies the supralittoral lichen flora.
3.6 Competition. Lichens may compete for space with rocky shore animals. Barnacle spat will overgrow littoral Verrucaria, especially V. mucosa and V. striatula, while conversely, it seems rare for lichens to oust the animals. However, Barnacle - Verrucaria communities seem to be dynamic, controlled by the success of Barnacle recruitment which varies considerably from year to year. Similarly seaweeds, especially crustose Hildenbrandia and Corallina, may out-compete lichens. However, protection is offered by the larger seaweeds, such as Fucoids, and lichens are usually found beneath their shade, often as pale coloured morphotypes. Verrucaria striatula is especially variable in this respect.
3.7 Competition with birds can be significant. In the supralittoral, birds can totally oust lichens by heavy build-up of guano on and below roosts. Isolated rocks used as bird perches may bear a very simplified lichen flora, but are sometimes dominated by species apparently dependent on bird lime, eg. Aspicilia leprosescens. In the supralittoral, a depauperate lichen flora may develop on very heavily used bird perches, containing Lecanora dispersa, Lecania erysibe, Rinodina gennarii, Xanthoria candelaria etc., typical of inland nutrient-enriched rocks. Since many seashore reserves are managed primarily for bird life, there is scope for conflict. Encouraging birds to nest or roost in new areas will certainly change the lichen communities. Therefore it is important that lichen communities be surveyed for critical species before such management changes are introduced. Introducing observation hides and visitor areas will increase human trampling on rocks and soil.
3.8 Agriculture. Man influences seashores below arable and pasture fields. Fertilizer dusts are the main concern, and are probably the greatest pollution threat to terrestrial lichens in modern times. To some extent seashore lichens are protected by waves and spray which rapidly wash away chemicals. But evidence of agrochemicals is noticeable on the supralittoral shore by build-up of green unicellular algae overlying lichen thalli. This can be very noticeable beside maritime golf courses. It is presumed that the excess nutrients are favouring the algal symbiont and so the symbiosis breaks down. The natural lichen communities are replaced by those which are pollution-tolerant, including species such as Candelariella vitellina, Xanthoria candelaria, X. polycarpa on twigs, Lecanora disperse, etc. Sometimes rocks affected by run-off water and around seepage cracks may be green with algae and lack damp rock or freshwater lichens such as Hymenelia lacustris, Porina chlorotica, Verrucaria internigrescens, V. prominula, etc. Planting of crops may not be a direct threat but run-off water, augmented by nutrients after seeping through soils exposed by ploughing, may affect lichens on the rocks below. Measures needed to prevent agricultural pollution are hard to define as this influence is ubiquitous and such chemicals reach lichens through water and air. Sites adjacent to farmland need assessing for their lichen interest if fertilizers are likely to be used nearby. It should be asked whether fertilizers are necessary, as maritime farmland is not particularly infertile. If fertilizer use is inevitable, then application should be done when the wind is onshore, to blow dust away from the lichen site. In extreme cases, hedgerow shelter belts could be introduced as a buffer between farmland and the upper shore. However, they will also affect the wave wind exposure of the site. Polluted water run-off could conceivably be diverted.
3.9 Trampling. This can occur by natural agencies such as Rabbits or birds, or by farm animals, usually sheep, cattle and horses but sometimes goats. Its effects inevitably accompany grazing (see above). Trampling by animals and humans, can be important in dispersing some lichens on soil, heath and dunes. Cladonia, especially the Reindeer Lichens, Coelocaulon, Teloschistes and possibly Heterodermia leucomelos seem to fragment easily and the liberated portions establish elsewhere. Trampling by humans will be heaviest in sites used by visitors. The effect is usually concentrated in well-defined pathways and can be very noticeable. Heavily man-trampled rocks and soils will be denuded of lichens, even polished. As trampling lichen communities on soil has both harmful and beneficial effects it is advised that the pressure be monitored so that the causal agents can be regulated.
3.10 Amenity. Seashores are well-used by people and areas near to sandy beaches may be denuded of lichens and occupied by seasonal sunbathers. Regularly used routes over rocks can be expected to be devoid of lichens, or the natural communities will be replaced by pollution-tolerant species. Excessive trampling is the greatest threat to soil lichens, on dunes, cliff edges, rock gullies used for access, and shingle beaches. It can also cause rock falls and remove important lichen populations. Unfortunately some lichens prefer the very places which humans find most attractive. A little recognized threat is from rock climbers on seacliffs. Hawksworth identified this threat in his flora of Derbyshire (1966) and the boot-polished rocks in popular inland climbing sites such as Cwm Idwal (Snowdonia) are devoid of significant lichen interest. Endangered maritime species, such asTeloschistes flavicans and Heterodermia spp., prefer short wind-clipped turf on cliff edges, which are ideal places for viewpoints. Soil Cladonia spp. often occur on short cropped turf near to car parks. Many lichens such as Ramalina siliquosa are well-developed on isolated rocks, again much favoured for sitting-on. It is noticeable that this species only achieves maturity (thalli of 10 cm long or more) on vertical, inaccessible rock faces. The well-known prescription for controlling amenity use is to restrict visitors to particular paths and areas, but this essentially writes-off the flora in those areas. Use of pathway markers and fences is effective. Nature trails are also beneficial, as the public can be informed why they should not trample a particular area. In extreme cases, visitors can be charged an entry fee, high enough to discourage excessive use.
Threats to lichens can sometimes occur from development - of beach huts, pathways, planting shelter belts, and recreational vehicles and bicycles on dunes. Even regular dog walking can eliminate lichens by trampling and fouling. This is noticeable near to car parks. It is clear that the only remedy here is to fully control visitor numbers, restrict where they go and what they are allowed to do.
3.11 Pollution. Although the media regularly inform the public about marine oil spills, remarkably little is known about their effects on seashore lichens. Recent studies include Ranwell (1966), Cullinane et al (1975), Brown (1975), Goudey, Dale and Hoddinott (1986), Lallement (1982) and Crump & Moore (1997). All authors concluded that decontamination measures using detergents, or more recently, high pressure water sprays, were more damaging than the oil itself. It is suggested that lichens can recover from oil spills naturally. Perhaps this is because those most affected are littoral, with gelatinous textures which resist absorption of oil. In the mesic supralittoral, some lichens seem able to grow out of the oil cover once it has hardened. They may even grow over it. So while the effects are unsightly, the population is not completely eradicated. Detergents and high pressure water or steam cleaning, however, which effectively sterilize the rock surface, will remove thalli completely. The contention that lichens may be tolerant towards high pressure water since they experience heavy wave action should be qualified. Many lichens are absent from shores experiencing heavy wave action; only a few are tolerant.
3.11.1 Little is known about air pollution on the seashore. Fletcher (1971 unpubl.) compared rocky shores near to industrial centres, principally the Clyde and Tyneside. These had simplified seashore lichen communities compared with shores away from sources of air pollution. The effects of chlorine released from a bromine works on the north coast of Anglesey were also found to simplify seashore lichen communities nearby (Fletcher and Jones 1975). Site managers can probably do little to control most air pollution since it is a global pervasion. Formerly air pollution was principally of particulates and sulphur dioxide emanating from domestic, industrial and energy generation sources, but their influence has declined dramatically since the early 1980's. Unfortunately, newer sources of air pollution are now thought to affect lichens globally, for example acid rain and agricultural chemicals (see above).
3.11.2 Fletcher (1976) found that seashore lichens were able to take up large amounts of potentially toxic cations such as cadmium and copper from seawater. However, the levels encountered did not visibly affect the lichens.
3.11.3 Lichens near to sewage outfalls have not been studied but casual sightings of abundant algal overgrowth would suggest that lichens could be affected by competition. Silt load in estuaries can simplify littoral communities so that they resemble those of saltmarshes.
3.12 Erosion and abrasion. Coastal erosion is a well recognized problem which obviously has a serious effect on lichens. Erosion by rockfall removes entire lichen populations. Newly exposed rock surfaces can be colonized by lichens, but as this is an extremely slow process it probably takes centuries to restore the original communities. A more insidious form of erosion occurs on boulder clay cliffs. This can be relatively slow and is weather-dependent, but is more rapid during heavy storms in winter. Fresh soil becomes exposed and washes down over rocks. Where this occurs regularly, the rock lichen flora can then be replaced by pollution-tolerant species. On the positive side however, is the colonization of freshly exposed soil by some rare lichens such as Rinodina confragosa, R. armeriicoia (non R. subglaucescens), and Acarospora benedarensis (currently subsumed within A. smaragdula, but with a very distinctive morphology and ecology). Coastal erosion is of national concern in times of rising sea levels, particularly in the South East. But it also follows human and animal trampling and grazing, which can be monitored and controlled (see above).
3.13 Misguided Management. Much disturbance of lichen populations results from well-intentioned but misguided management. Examples are use of fire to control scrub, planting of trees which replace soil floras, or shelter belts reducing the exposure factor for a site. Clearance of scrub can eradicate important lichens. For example Teloschistes chrysophthalmus, once thought extinct after removal of a hedgerow, was refound on a moribund Blackthorn. It is now extinct once more following loss of the Blackthorn. Spraying with weedkillers regularly takes place, especially around man-made sites which may often be considered erroneously as unimportant for lichens. Much management appears to be needless as it is often stimulated by a desire for tidiness. The ready availability of chainsaws and volunteers trained in their use, especially near high population centres, means that management is eagerly undertaken, but the need for it may be unexamined. To prevent needless destruction of lichen habitats it is recommended that all management plans for sites with notable lichen interest should be commented on by a lichenologist.
3.14 Wall restoration. Walls offer considerable opportunities for colonization by marine and maritime lichens. In lowland Britain where rocks are not exposed on the shore, walls of brick, concrete or flint may bear the only seashore lichen floras, adding considerably to the biodiversity of the site. Generally however, walls have a less rich lichen flora than natural rocks because they are much younger. Fletcher (1997) found that walls near to habitations had the richest lichen floras because they were the most useful and were therefore better maintained, but they were not necessarily the oldest. However, wails obviously need restoration and maintenance. To preserve their lichen floras the following guidelines are proposed -
- Patchwork restoration over a period of years is better than razing the wall to the ground and rebuilding it.
- Cement or concrete should not be used on siliceous drystone walls.
- Stones with particularly interesting, rare or endangered species should identified and marked and replaced in the same location, bearing in mind its original height on the wall and its aspect to light.
- Neighbourhood planting should be avoided because of the shading factor.
3.14.1 Ironwork is often associated with man-made walls and habitations. Old, exposed iron can bear interesting lichens, particularly Bacidia, Micarea and Vezdaea spp. As these are taking opportunity of the natural rusting process it is difficult to apply conservation management to this situation. However, protective paints must be avoided.
3.15 External Activities. Many sites are threatened by activities beyond their boundaries. Some examples have been dealt with above. We can add depletion of the water table by drainage and gravel extraction, agricultural improvement, golf course management, caravan parks, etc. Finally, quarrying has been a great threat in the past and remains so, particularly with the recent proposals for superquarries in the Western Isles. However, it should also be pointed out that many rich seashore habitats are the result of old quarrying activity and generally the floras become richer the longer the quarry has ceased to operate.
3.15.1 The site manager needs to remain continually aware that lichens can be seriously damaged from activities outside the site.
3.15.2 Accidents can be placed in the same category. Seashores may become depopulated of lichens by a variety of accidents, only some of which may be recoverable. Examples noted in the past include grounding of boats which scrape off entire rock surfaces, rock falls caused by weather conditions, storms, etc., natural population explosions of animals which increase grazing, manuring and trampling (see above), fires amongst higher plant cover (this may be a misguided management practice (see above), overgrowth by higher plants as part of a natural succession in the absence of grazing pressures, and so on.
4.1 The main recommendations from this review are as follows -
4.1.1 Lichenologists should be consulted when management plans are being drawn up.
4.1.2 The site under consideration needs to be surveyed to determine its lichen interest and to locate the valuable or sensitive areas.
4.1.3 The need for management should be questioned in every case as much of it is probably unnecessary, especially when the intention is cosmetic.
4.1.4 Visitors to sites should be made aware of lichen interests so that damage due to ignorance is minimized.
4.1.5 Since few of the proposed lichen habitat management guidelines have been tested, it is important that operations be monitored, reviewed and the plan revised accordingly. All management at the present time should be considered experimental.
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