The paper-reading meeting held in the Department of Biological Science, University of Lancaster, on the weekend of September 19-20, was ideally situated to provide a convenient meeting place for members from all over Britain. It was therefore pleasing to see that England, Scotland and Wales were all well represented by those members who had taken advantage of the opportunity. They were well rewarded by the high standard and variety of topics covered by the speakers, who were introduced by the Vice-President. Contrasting pictures of the bryophyte floras of areas close to Lancaster were presented and a look at aquatic bryophytes from the Antarctic reminded us that similar adaptations have been reported in the English Lake District. Also included was an interesting survey of historical changes in the British bryophyte flora and a wide-ranging and thoughtful consideration of conservation needs. In some ways, the latter was complemented by the speaker who advocated photographic re cording of species and went on to demonstrate his skills in the art. Summaries of these papers are given below.
Dr M. C. F. Proctor (Exeter): “Mosses and liverworts of the Malham Tarn district.”
Malham Tarn lies almost midway between John o ‘Groats and Lands End, and close to the Pennine watershed; with its varied topography and geology, its surroundings have a rich and interesting bryophyte flora. The district lies in one of the major areas of Carboniferous Limestone in Britain. Calcicole species are conspicuous, and a number of rare limestone species have their British headquarters here, e.g. Pedinophyllum interruptum, Zygodon gracilis, several Seligeria spp. Acid substrata include Carboniferous shales and grits and Lower Palaeozoic slates, and glacial drift and peat The mire complex of the Tarn Moss and fens is a major element in the habitat diversity of the immediate surroundings of the Tarn. Bryophytes are important in defining some of the main phytosociological divisions in mire vegetation, which in turn provide a useful framework for comprehending patterns of bryophyte distribution and suggesting the habitat factors that determine them. Like other hilly areas, the Malham district is a meeting place of northern and southern species. The latter tend to favour sheltered or south-facing lowland sites ( e.g. Isothecium striatulum, Cololejeunea rossettiana) while the former generally occur at higher altitude and often in shady or damp north-facing situations (e.g. Distichium capillaceum, Orthothecium rufescens, Pseudoleskeella catenulata, Anastrepta orcadensis); some similarities and differences in the distributions of these species were discussed.
Dr P. Ferguson and Dr J. A. Lee (Manchester): “Sulphur pollutants and the growth of Sphagnum species in the Southern Pennines.”
The disappearance of Sphagnum species from the blanket bogs of the Southern Pennines has occurred during the last 200 years. Several factors may have been responsible for this, but atmospheric pollution is a probable cause. Experimental fumigations of several Sphagnum species with SO2 have demonstrated that the most abundant species in the region to-day, S. recurvum, is the most resistant to this pollutant and other species formerly abundant, e.g. S. imbricatum and S. tenellum, are very sensitive to it. A similar response has been demonstrated in artificial rain experiments conducted at an unpolluted bog in North Wales with the solution products of SO2, ¯ ¯HSO3 and ,¯SO4. These experiments were performed with concentrations of sulphur pollutants within the range of those likely to have occurred in the past in the S. Pennines, and so it is probable that these pollutants have at least contributed to the disappearance of Sphagna there.
Since the clean air acts the levels of sulphur pollutants have fallen dramatically in towns and possibly also in rural areas. Transplants of Sphagna into high watertable sites in the blanket bogs of the S. Pennines still grow very poorly compared with transplants to similar situations in North Wales. The cause of this is still being investigated, and may involve an interaction between present-day atmospheric sulphur and nitrogen pollutants and previously deposited pollutants stored in the peat.
Dr J. H. Dickson (Glasgow): “Recent additions to the Quaternary moss flora.”
Dr H. J. B. Birks (Cambridge): “Rare and endangered bryophytes in the British Isles: a case for conservation.”
For its size Britain supports one of the richest bryophyte floras in the world, with many Atlantic, Continental, and Arctic or Arctic-Alpine species growing at or near their northern, western, and southern limits respectively. The purposes of nature conservation were discussed. The holistic concept of nature conservation is of little direct use in practical conservation of wildlife. Economic aspects (forestry, agriculture, fisheries water use) frequently conflict with wildlife conservation. The main purpose of nature conservation is cultural, both scientific-educational and aesthetic-recreational.
Within the British bryophyte flora, conservation interests should centre on those species whose survival is currently threatened by the rapid loss of natural and semi-natural habitats in Britain.
Threatened endemic or near-endemic species (6 in total) include Cephalozia hibernica and Herbertus borealis. Threatened rare species (plants with one or a few localities; 61 species) include Seligeria carniolica, Leiocolea rutheana, and Acrobolbus wilsonii. In addition there are 22 locally rare species that appear to be declining, including Homalothecium nitens, Orthodontium gracile, and Orthotrichum obtusifolium.
The present rate of habitat destruction in Britain is such that all natural or semi-natural habitats will have been reduced by at least 50% in the next 20-30 years. Major threats to bryophytes include coastal development, mire drainage, changes in land-use in both the lowlands and the uplands, woodland loss, changes in countryside practices, atmospheric pollution, stream and river pollution, and collecting.
Dr J. Priddle (Bangor): ” Bryophytes in Antarctic lakes.”
Aquatic mosses are an important element in the benthic vegetation of some nutrient-poor Antarctic freshwater lakes. Studies have been carried out on Calliergon sarmentosum (Wahl.) Kindb. and Drepanocladus cf. aduncus, which dominate the benthos of Moss Lake, Signy Island, South Orkney Islands.
The lake had an extreme irradiance environment in winter, with ice and snow on the surface drastically reducing incoming solar radiation. In spite of this, net O2 production by the moss community (measured in situ) was recorded in August, only two months after midwinter. The moss community was estimated to be above compensation for c. 10 months each year. Laboratory studies confirmed very low compensation irradiances for both species of moss at normal lake temperatures. However, compensation irradiances were greatly increased at higher temperatures, suggesting that the survival of aquatic mosses under low winter irradiances may be attributable partly to very low respiration rates at ambient lake temperatures.
Both species exhibited robust morphologies with large leaves and long internodes. Shoots of terrestrial Calliergon sarmentosum cultured in the lake or submerged in the laboratory also developed this habit. Increased Leaf Area Index of the robust morphology may also be a factor in the survival of mosses in low irradiance conditions but it appears to arise in response to some other stimulus. The growth form of aquatic Calliergon was very plastic, the species forming dense stands of microphyllous stems in shallow water but growing as robust stems intermixed with Drepanocladus in the deeper parts of the lake.
The presence of dense stands of aquatic moss increased habitat diversity in the lake and contrasted with the other major component of the benthos which was an undifferentiated algal ‘felt’. Moss stems were colonized by a wide variety of epiphytic algae and attached and free-living microfauna.
Dr S. R. Edwards (Manchester): ” Bryophyte photography.”
Photography was considered solely as a means of collecting and recording as much useful information about bryophytes as possible. Although general and habitat shots are certainly valuable, the lecture was restricted to magnifications of x1.0 and higher because of limited time. The particular value of x1.0 as a standard was stressed not only for comparison between slides, but also between slide and moss. It was noted that dry mosses are easily wetted (rather than vice versa), so for comparative purposes a wet shot should always be included.
Having briefly considered the functions and merits of a Single Lens Reflex camera, we looked at the simplest flash and camera setup which can be carried around as a unit to “hammer bryophytes whilst on the trot”. The problems of single-flash photography, such as illuminating very close subjects and reducing contrast, were considered. We then discussed the best kind of lens to use for various magnifications, and the practical problems associated both in the field and indoors.
Photography, particularly in close-up, is the art of compromise. At high magnifications the Depth of Field shrinks dramatically, needing very small apertures; but such apertures cause an overall loss of sharpness due to diffraction. To help decisions to be made, graphs were shewn of D. o. F, (against aperture at varying magnifications from x0.1 to x10) and also of resolution (using the same format). This second graph was primarily designed to read resolution on the ground rather than the film, so that a bryologist could easily see what size cells or spores would be resolved. Examples were shewn using Plagiomnium undulatum at x1.0, where the 15µm cells were resolved at wider apertures, but vanished when the lens was stopped down to achieve better D. o. F.. P. affine, having cells of 30-50µm, can, however, usefully be photographed at smaller apertures.
Being able to measure cell size is obviously useful in identifying mosses from slides, but it was stressed that this wasn’t the sole criterion. Several other aspects were considered, such as balancing available light with flash, and using teleconverters for effect, but in particular the use of the 24mm f / 2.8 wide-angle lens, reversed, for magnification of about x7.5, was recommended. The lens should be one of those with “floating elements” to correct aberrations when focussed close. Eight advantages were given for the use of such a lens:
1) short focal length needs fewer tubes;
2) competitive focal length, thus both good and cheap;
3) doubles as wide-angle;
4) almost exactly half 50mm standard lens’ length, thus making calculations neater;
5) floating elements give excellent image at about 1:7 (normal closest focus), and reciprocally at about x7 when lens reversed;
6) retrofocus design gives good working distance, e.g. 45mm at x7.5, which is nearly twice focal length of lens;
7) pupillary magnification (i.e. optical asymmetry) for this kind of lens is generally 2.0, making aperture calculations easier;
8) f / 2.8 gives much needed extra brightness for focussing.
Our final speaker was Dr S. W. Greene who, in his Presidential Address, discussed ways in which the Society might develop in the future. This was followed by the annual general meeting (Minutes in Bulletin 40) and, in the evening, by a conversazione during which a number of exhibits were displayed. These included the following.
|Mr D. G. Long:||Barbula jamesonii and related literature|
|Dr H. L. K. Whitehouse:||Aulacomnium palustre with gemmae in agar culture.|
Despite the depressing weather prognosis, the Sunday excursion was bright but cold. Roeburndale Woods, Lancashire (Grid ref. SD6066) were visited first. These are northern mixed deciduous woods lying on Carboniferous shales and sandstones that give a range of neutral to acid soils. The woods were chiefly notable for the luxuriance of the bryophytes. Among the species recorded were: Barbilophozia attenuata, Jungermannia atrovirens, Epipterygium tozeri, and Rhytidiadelphus subpinnatus. After lunch at Ingleton, the wooded ravine of Ling Gill, W. Yorkshire (Grid ref. SD 8078) was visited. Trees of ash, elm, birch and aspen clothe the sides of the ravine which is cut into Carboniferous Limestone. The moist sheltered conditions have resulted in a rich bryophyte flora, among which the following species were recorded: Apometzgeria pubescens, Pedinophyllum interruptum, Hylocomium brevirostre and Seligeria acutifolia. Tortula subulata var. graeffii was found on a wall by the roadside where the cars were parked. Epipterygium tozeri and Rhytidiadelphus subpinnatus were new county records, both for VC 60. I am very grateful to those members who supplied lists of species, particularly for the Roeburndale Woods from which no comprehensive bryophyte list exists. Any further additions would be gratefully received.
A. J. C. Mallock
This was an enjoyable and worthwhile meeting and, for his efforts in making it so, the Society is indebted to Dr Malloch. Heavy over-night rain threatened the success of the field excursion but events suggested that even the weather was under control.