The success of the joint BBS/BES symposium was no accident: the programme had been constructed with thoroughness and skill by Royce Longton such that the presentations meshed together with precision, and the local organisation by Philip Lightowlers was equally exemplary. It is worth recording our thanks to them for this excellent conference at the beginning of this account, rather than losing it in an acknowledgement at the end.
The 74 participants who enjoyed this symposium were from 18 countries and, although 34 were from the UK, the number also included 6 from Canada, 3 from the USA, one from South Africa and one from Australia. The numbers attending were such that it was possible to speak to most people there, and we were complimented by the great fluency in English of those for whom it is not their first language.
It was a meeting that demonstrated the depth and increasing influence of bryophyte ecology. The real triumph of the programme was the way in which apparently unconnected topics were synthesised to present an ecological whole. Bryophyte production (the theme of the first session) and nutrient cycling seemed to recur throughout the three days, even in some of the contributed papers, presenting a very satisfying view of the significance and relative importance of bryophytes in relation to other plants. Some surprising conclusions were drawn: Dale Vitt calculated leaf production of a moss plant at one leaf per hour, whilst Terry Carleton, in a poster presentation, found Canadian forest floor bryophytes as productive as the tree canopy. In particular, it was emphasised several times, bryophytes should not be seen by botanists as operating as scaled down phanerogams.
The abstracts for all but 2 of the 24 talks and for most of the posters were available in a booklet at the start of the first session, and the full proceedings will be published by the Linnean Society. I thus apologise in advance for the crude generalisations made below, and refer you to the proceedings for a more accurate picture.
Session 1: Bryophyte production and decomposition.
Sean Russell looked at production and decomposition in tundra ecosystems – an environment where bryophytes attain their maximum relative importance in terms of biomass and production. He described various methods of measuring these, and regretted the shift of emphasis away from autoecological studies at a time of increasing human impact, particularly in the northern tundra biome.
Dale Vitt described a great variety of research underlining the dynamic, highly active nature of bryophytes, concentrating more on the systems in which they exist. He looked first at the complex canopies formed by mosses (many having 6000 leaves per square cm) and their high growth rate. Limitations to growth rate were shown to depend on the interaction of the plant’s drought tolerance with the climatic and nutrient limitations of the environment. He next looked in more detail at production in bogs and fens concluding that hummocks appear to be maintained in bogs due to low decomposition rates, while in rich fens they are maintained by relatively high production. The need for much fundamental research in this area was emphasised throughout, as was evidenced by the fact that such a prime boreal bryophyte habitat as a mire was so poorly understood – for instance, the considerable variation in pH of a rich fen through the year seemed to be a surprise to many in the audience.
Jan-Peter Frahm also took a ‘whole biomass’ approach in discussing productivity in the tropics. He compared his experience on the BRYOTROP expeditions to Peru and Borneo with other data, principally from Pocs, to provide some explanations for the increase in bryophyte phytomass from lowlands to uplands in tropical forests. Gradients of temperature, precipitation, humidity and desiccation contribute, but experiments on gas exchange in tropical montane bryophytes (confirmed with temperate bryophytes) reveal that the rate of net assimilation decreases dramatically above 25°C, and that high temperature combined with low light intensity, as occurs in tropical lowland forests, results in inadequate net photosynthesis. The effect of high nutrient supply in tropical montane forests, and the effect of strong desiccation in the lowlands, have yet to be studied.
Michael Proctor ended the session with a presentation on the physiological basis of bryophyte production. Bryophytes operate normally as typical C3 plants, but are affected in their expression of this by their small size and frequently poikilohydric habit. Many species are tolerant of desiccation to the level of ca. 5-10% of dry weight, and photosynthesis declines with water loss and recommences, with variable delay, after remoistening. Although their ability to recover, and the speed of recovery, vary, most bryophytes, including those of well illuminated habitats, operate as shade plants. The physiological aspects of this were considered in more detail, but the conclusion was that growth forms (which strongly influence both storage capacity and rate of water loss) were largely determined by a balance between water economy and the need for carbon and mineral nutrient acquisition.
Session 2: Interaction between bryophytes and other organisms.
Denis Brown considered nutrient cycling, which became one of the major themes of the symposium. Direct information on nutrient cycling through bryophytes is limited and often incomplete, but the known ways in which mineral nutrient elements were acquired and lost elsewhere in the plant kingdom were reviewed, and work was described that attempted to locate where nutrient elements were located in moss cells, and how they were moved about the plant.
Heinjo During reviewed bryophyte interactions with other plants, concluding that the view that bryophytes exist in “ecological isolation” from other plants was true only so far as competition is concerned, and that bryophytes are involved in a variety of parasitic, symbiotic, mutualistic and other as yet unspecified interactions with vascular plants, algae, fungi, lichens and bacteria. These interactions are largely unresearched, but such information is essential for understanding the ecology and ecological role of bryophytes.
Aune Koponen discussed entomophily in the Splachnaceae – the only moss family where this has been observed. Three kinds of adaptation were considered: substrate tolerance, morphological and chemical. Splachnaceae show a greater tolerance experimentally than other families to high nitrogen substrates, and arctic Splachnaceae have been shown to have a higher nitrogen concentration than other arctic bryophytes – both competitive advantages. Morphological adaptations are the enlarged coloured hypophysis, the coloured upper part of the seta, the hygroscopic movements of the capsule wall and peristome and the small thin-walled spores, suitable for insect distribution. The chemical adaptations are all in the sporophyte, which produces and releases odours, in particular volatile octane derivatives.
Alison Davidson described her research on slug damage to bryophytes (already featured in the popular scientific press: New Scientist No. 1582, 15 October, 1987). Palatability of different parts of mosses to slugs was tested experimentally, and the slugs were shown to prefer protonemata and immature capsules to mature capsules and leafy shoots, but the degree of this varied between moss species. Moss shoot extracts presented on communion wafers appeared to be more acceptable, suggesting that the cell wall provides the barrier to free consumption. It was suggested that phenolic compounds incorporated in the cell walls may be responsible.
Sessions 3 and 4: Contributed papers.
Lars Söderström looked at the concepts of rarity within a geographical area, and rarity in relation to the localities available to a plant within that area. Using bryophytes growing on rotten logs in Swedish spruce forests, he distinguished four groups: core, urban, rural and satellite species. Method of dispersal was the main distinguishing feature of the groups, and they were discussed in connection with the use of indicator species and effects of habitat fragmentation.
In the Burren (western Ireland), Grace O’Donovan found that productivity of bryophytes was greatest in spring and early summer (up to 25%), before flowering plants provided too much shade.
Bart van Tooren, using experiments both in the laboratory and in chalk grassland, found that use of fertiliser does not stimulate the growth of bryophytes in the field, and that nutrient supply is not limiting to growth. This was discussed in relation to air pollution in the Netherlands and its effect on bryophytes.
Nils Malmer has examined four hummock-forming sphagna chemically, to determine where particular elements accumulate, in relation to their growth, locality and productivity.
Roger Daniels has used isozyme banding patterns to determine differences in genetic variation in Sphagnum, but concluded that environmental effects caused sufficient interference to make the method inconclusive.
Alan Silverside examined sulphur tolerance in two common mosses in urban environments, suggesting that their adaptation was ecotypic.
Angela Newton described research that revealed that moss fragments always germinate better than spores in Tortula, spores germinate and grow better if kept continually moist, but that germination of both spores and fragments was significantly reduced if grown on moss clumps (whether or not Tortula). This inhibition appeared to be due to a water soluble substance.
John Lee looked at variation in Sphagnum responses to mineral deposition based on polluted and unpolluted sites.
Session 5: Population Biology.
Royce Longton discussed research attempting to assess the functional significance of reproduction by spores. Most moss species produce spores, and where sporophytes are unknown, the plant tends to show a narrow distribution with relatively few varieties. Although spores are deposited at high density near to the plant, the majority are dispersed to greater distances. In the laboratory, spore germination is often straightforward, and was very effective in the field for an annual fugitive species but for a long lived perennial (Atrichum undulatum) field germination failed totally, and it was confirmed by transplant experiments and field observations that vegetative propagation plays a major role in colony maintenance in this plant.
Martha Newton reviewed the extremely limited information about the genetic structure of hepatics, this paucity being attributed largely to the practice of phenetic species definition (sometimes in conflict with genetic evidence) and a concentration on observation rather than experimentation. There exist several cytological and genetic techniques that could elucidate many of the problems in the hepatics, and both the problems and techniques were listed.
Nancy Slack showed that classical niche theory needed to be adapted for the bryophytes. Various recent work was reviewed, with special reference to Sphagnum, Splachnaceae, bryophyte communities in streams and ephemeral bryophytes. Some communities seem to have equilibrium characteristics, with species with relatively narrow niches and little or no overlap, but in most bryophyte communities diversification of bryophytes in microhabitats is opportunistic. Some Sphagnum communities demonstrate complete saturation by species that have realised niches determined by competitive interactions, but this is unusual for bryophytes.
Philip Grime placed bryophyte strategy theory in the context of all green plants, looking in particular at variation in bryophyte life histories, form and physiology, in relation to three patterns of specialisation recognised in flowering plants: establishment strategies, regenerative strategies, and attunements of growth to different seasonal patterns of variation. He concluded by looking at the probable consequences of climate warming on bryophytes (very significant!).
Session 6: Bryophytes and man-modified ecosystems.
Germund Tyler reviewed the now extensive literature on heavy metals and bryophytes, including mechanisms of metal uptake, retention, toxicity and tolerance. Differences between species were discussed, including the development of extreme tolerance. The use of bryophytes in monitoring heavy metal deposition was considered, and comparisons made with direct deposition measurements.
Peter Beckett showed the disastrous results of metal smelting at Sudbury, Canada over the last 100 years, which has resulted in 450 square kilometres of metal contamination and depauperate vegetation cover. Spore germination tests, growth experiments and transplants indicate that Sudbury populations are more tolerant to pH, Ni, Cu and Al than control populations outside the area.
Agneta Burton reviewed the research on bryophytes as monitors of contamination, describing the approaches used and the results obtained from monitoring both terrestrial and aquatic bryophytes in urban and industrial habitats, from a range of countries, including the tropics; there is a great interest in such relatively low cost methods of monitoring pollution.
Dan Norris, referring to earlier presentations, reassured his audience that he would talk about neither numbers nor Sphagnum, and discussed mainly water relations of bryophytes in various tropical conditions.
|I. Bisang||Differences in the habitats of epiphytic Frullania dilatata, F. tamarisci and F. fragilifolia in Switzerland.|
|G. Brumalis and T.J. Carleton||Shoot growth in Pohlia nutans.|
|T.J. Carleton||Bryophyte and terricolous macrolichen distribution along a combined nutrient and moisture gradient in the boreal forest of central Canada.|
|N. Cronberg||Hybridisation in the Sphagnum capillifolium group.|
|G.M. Dirkse, H.C. Greven and H.M. van Melick||Mosses in Dutch urban environments.|
|A.M. Hobbs||Leafy liverwort-rich Calluna vulgaris heaths in Scotland.|
|A. Hofman||Genetic structure of populations of three Plagiothecium species with contrasting mating systems.|
|B.G. Jonsson||Diversity patterns of bryophytes in a virgin spruce forest – the effects of uprooted trees.|
|T.A. Kavanagh and T.J. Carleton||Feather moss distribution and production beneath individual black spruce tree-crowns in relation to precipitation and throughfall hydrochemistry.|
|D. Lamy, J. Perreau and H. Bischler||Les “Surmousses”: illustrations of bryophyte-fungal associations of the 18th and 19th centuries.|
|P. Lightowlers||The ecology of wall mosses.|
|F. Lloret||Establishment and population dynamics of Tayloria tenuis in a Pyrenean forest.|
|M. Newton||Pellia borealis Lorbeer, an epithet of practical use.|
|B.J. O’Shea and J.-P. Frahm||The IAB Software Library.|
|B. Wickerson and S.H. Hillier||Interactions between bryophytes and higher plants in vegetation gaps.|
|M.O. Hill, C.D. Preston and A.J.E. Smith||BBS mapping scheme and atlas.|
Many members accepted the invitation of David Long to visit the Edinburgh Botanical Garden and the Herbarium during the week, and he also led an evening excursion to the glasshouses on Thursday. All were impressed with both the garden and herbarium – particularly the latter with its space, calm and order and fully accessioned collections, with plenty of bench space and microscopes for visitors.
During the week, a determined attempt was made to sample the restaurants and beers Philip Lightowlers had recommended in his useful background material, and those who succumbed became firm fans of 80 shilling beer and Indian food.
The field excursion on Friday, organised by David Long and Philip Lightowlers, was to sites only a few miles from the centre of Edinburgh, but with bryophytes unusual for an area in a semi-industrial setting. The coach delivered us first to Roslin Glen, about 7 miles south of Edinburgh, an attractive wooded glen with a deep shady ravine cut through Lower Carboniferous sandstone. This is the type locality for Tetrodontium brownianum, where it was discovered by Robert Brown nearly 200 years ago, as well as a site for Orthodontium gracile. Although the latter was not found, the former was seen on a vertical sandstone rock by the river. Barbilophozia attenuata, Nowellia curvifolia and Dicranum tauricum were found on logs, Metzgeria fruticulosa on an elder and Orthodontium lineare on stumps and tree bases. Before getting back on the coach, many also visited Roslin chapel, a remarkable 15th Century building, the stone uncharacteristically co vered with carving. On a footpath Jean Paton noted Riccia sorocarpa.
Lunch was at Balerno, and we needed only to stagger a couple of hundred metres from our three course lunch to the next site – Red Moss, a large area of blanket bog. Here were recorded Kurzia pauciflora, Scapania gracilis, Odontoschisma sphagni and at least six species of Sphagnum.
This was the end of the meeting, and on Saturday we departed either home or to Beauly, Inverness, for the field meeting.