Bryophytes of springs and flushes - 2009 course notes - Plantlife

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BRYOPHYTES OF SPRINGS AND FLUSHES Springs and flushes are an extremely important habitat for bryophytes and mosses and liverworts often form a significant proportion of the biomass. Bryophytes have a significant presence in at least 12 National Vegetation Classification (NVC)* spring and flush communities and a number of these correspond to categories on Annex I of the Habitats Directive; the more important of these are briefly described below. Spring and flush communities vary widely in species composition, ranging from the acidic, and often extensive, M6 Carex echinata – Sphagnum fallax mires to the strongly calcareous, and usually small, M38 Palustriella commutata – Carex nigra springs. Springs and flushes may be dominated by just a small number of common bryophytes or may have a diverse flora with a number of rare and scarce species. There are 41 bryophyte species of conservation interest that have at least some important populations in springs and flushes and some of these are confined to this habitat; these species are listed with their status in Table 2. Of this long list, 10 are BAP species, eight are considered Vulnerable or Endangered in the Bryophyte Red Data Book, four are on Schedule 8 of the Wildlife and Countryside Act, one is included in a list of the world’s most threatened bryophytes and one is listed in the Bern Convention and on Annex IIb of the EU Habitats and Species Directive. (*NB The National Vegetation Classification (NVC) is a comprehensive classification and description of the plant communities of Britain, each systematically named and arranged and with standardised descriptions for each. More details can be seen at http://www.jncc.gov.uk/page-4259 The NVC categories have been used as a structure for describing species on this course). What are springs and flushes ? Springs are usually the point source of a burn, where the water-table meets the ground surface, and so there is often a series of springs across the slope at much the same level, which, appropriately enough, is called the ‘spring line’. Springs are usually small and welldefined and often have a complete cover of bryophytes with just scattered flowering plants. Flushes are areas where the flow of ground water is more diffuse, either where the water table reaches the surface or where or where water flows widely over the surface of saturated ground rather than in a well-defined channel. They can be areas of open, stony ground with only a sparse plant cover or have a complete and often dense cover of vascular plants, usually sedges or rushes, with the bryophytes forming a ‘ground layer’ under this ‘canopy’. We tend to think of both springs and flushes as particularly associated with open habitat in the upland areas of Scotland but they can occur right down to sea level and under a woodland canopy, where they seem to be close to M36, but obviously the species composition will tend to differ markedly in each case. The vegetation associated with the various springs and flushes is determined by the physical character of the habitat, particularly the temperature and the mineral content of the water. In terms of diversity of species, the NVC communities M10, M11 and M12 where the groundwater is moderately or strongly calcareous are by far the most important but the icy, nutrient-poor meltwater springs and flushes M31, M33 and the higher level M32 stands are also of conservation concern as they are so restricted in their distribution. However it is interesting and perhaps instructive to note that the BAP species are scattered through a variety of flush types, with the most threatened of them at relatively low level. 2
Threats Climate change A number of flush communities, particularly those with Pohlia wahlenbergii var. glacialis and Pohlia ludwigii which are dependant on the cold water associated with areas of late snow-lie are clearly under threat if the pattern of snow accumulation and persistence changes. There is good evidence that the pattern and duration of snow lie in Scotland is already changing. Over time there may well be other changes as part of a complex shift in plant communities and their spatial distribution as a result of what will probably be a warmer and wetter climate. Pollution Though most springs and flushes are well away from the sources of pollution, the vegetation is still under threat from sulphur and nitrogen deposition which is enhanced by the heavy rainfall and deposition in droplets of mist when the hills are cloud-capped. Mosses and liverworts are particularly susceptible to this kind of pollution. A particular problem in the higher hills is the concentration of pollutants in the snowpack, built up over the winter, which can then be suddenly released through a rapid thaw, the ‘acid flush’ which can kill fish downstream. The long-term effects of this pollution are unclear but it must have some effect on the bryophytes which have no protective cuticle and so absorb water and pollutants directly into the cells of the leaf. Drainage By their nature, springs and flushes occur in wet places and so have always been threatened by changes in the local hydrology. The most obvious threat is by drainage, gripping an area to improve it for grazing or the planting of trees. The more extensive flushes are often the main casualty of this form of management through direct damage and a prolonged drying out of the areas affected. It is quite remarkable how much of this went on, presumably when grants were available, and it is not unusual to come across patterns of ditches in quite remote upland areas. This era has now passed and gripping in upland areas is rare but it this threat has been replaced by that from the changes in hydrology that occur as a result of the construction of the infrastructure necessary to service windfarms. All windfarms require service roads to each turbine and these, plus the associated ditching and drainage will change the hydrology of the affected area as well as having a more direct local effect. The only Scottish site for the BAP liverwort Pallavicinia lyellii, in flushed Molinea caerulea grassland, is now part of the huge Eaglesham windfarm. A planned windfarm in the Ochils will affect a large population of Hamatocaulis vernicosus (Bern Convention, EU Directive Annex IIb, Schedule 8 WCA). Apart from the flushes destroyed by the construction process, it is not known what the effects of the changes in the hydrology in the flushes might be and it is unlikely that any monitoring work has formed part of the mitigation. Forestry In the past, blanket aforestation has destroyed springs and flushes over a vast swathe of Scotland but particularly so in the south and west. In Cowal, Argyll, for example, above the valley bottom, there are very few slopes without commercial plantations, many well into their second rotation. The process of blanket aforestation of open hill land with commercial conifers has diminished considerably in recent years but springs and flushes, being small scale features, are still vulnerable. One, rather ironic, threat is from the commendable zeal for the expansion of broadleaf and native Scots pine woodland, where the drive to increase woodland cover tends to overpower the consideration of diverse small-scale habitats like springs and flushes. On Rhum, such planting was probably responsible for the demise of Hamatocaulis vernicosus in its one site on the island. Some crofting woodland schemes in Sutherland where sites have been scarified before planting are also poorly designed in this respect. Even exclosures to 3
Page 1: LOWER PLANTS AND FUNGI PROJECT - TR
Page 5 and 6: often having only large stands of c
Page 7 and 8: M31 Anthelia julacea - Sphagnum den
Page 9 and 10: M36 Lowland flushes There are a var
Page 11 and 12: Typical flush species Sphagnum palu
Page 13 and 14: Pohlia wahlenbergii var. glacialis
Page 15 and 16: The BAP species Andreaea nivalis Th
Page 17: Splachnum vasculosum Another member

Bryophytes of springs and flushes - 2009 course notes - Plantlife

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