Palaeoecological investigations of changes in the composition of ombrogenous raised mire and fen vegetation at Rhos Goch National Nature Reserve, Mid Wales

Plant macrofossil analysis, macroscopic charcoal analysis, spheroidal carbonaceous particle analysis and radiocarbon dating have been completed on the raised bog deposits at Rhos Goch Common to examine the history of peat accumulation and vegetation change at the site. Two full-depth peat profiles were studied from the bog plane and the margin of the peat dome, respectively. A further three short cores were located on contrasting bog surfaces to study recent pool, lawn and hummock development. The results of the investigation show that the modern floristically-impoverished vegetation is a relatively recent development. During the mid- to late-Holocene the site supported a range of ombrotrophic Sphagna including Sphagnum imbricatum and S. magellanicum. Stratigraphic logs and radiocarbon dating demonstrate that a significant part of the raised dome margin is missing. The most likely explanation for the missing peat deposits is that the site has been exploited for peat in the past, since there is little evidence to suggest that recent fires were any more severe than those occurring naturally in the early-Holocene. The impact of peat removal has been significant. There is clear evidence that the bog water table has fluctuated over a wide range causing accelerated secondary decomposition in the catotelm right down to the level of the fen-bog transition

Review of the routes to ombrotrophy in raised bogs from Britain and Ireland

The development sequences of fourteen raised bogs from Britain and Ireland are reviewed. Plant macrofossil and radiocarbon evidence suggest that hydroseries can become ombrotrophic in both hyper-oceanic and suboceanic conditions but the character of the fen-bog transition varies in each case. In highly humid conditions true raised bog communities can develop directly over swamp, fen and fen carr and the mire water table can remain near the surface throughout the transition. In sub-oceanic conditions bogs may develop towards ombrotrophy via an Eriophorum vaginatum/Calluna-dominated stage in which very highly humified peat is laid down. This peat, which has a very fine pore structure, may act as a foundation for the development of a raised water mound. True oceanic Sphagnum-rich bog, with a near surface water table, may develop later as a result of a climatic shift towards higher effective precipitation. Bogs can also become raised because of a change in the local drainage basin conditions. Disruption of the ground and surface water supply can lead to isolation of the peat surface and a switch to oligotrophic conditions

Coring and assessment of the lagg fen at Cors Caron NNR, Ceredigion, Wales

Five sample cores were taken from two areas of lagg fen surrounding Cors Caron West Bog and described using the Tröels-Smith system of sediment classification. Two cores were selected for further laboratory analyses; one (Lagg2) was located near to the western hill slope margin and the other (Lagg5) on the banks of the Teifi river channel. Plant macrofossil analyses of core Lagg2 showed that peat development began in a marginal woodland, which was overtaken by a relatively dry raised bog community. The bog developed for several thousand years and was eventually invaded by low hummock and lawn Sphagna typical of wet oceanic raised bogs. At the same point the Sphagnum-rich peat shows signs of disturbance in the form of charcoal layers and an increase in soil fungi. These features may represent secondary decomposition after peat cutting. The bog assemblage is abruptly replaced by a wet fen assemblage that may represent in-filling of an abandoned peat cutting. Lagg2 is almost certainly not an intact sequence and the modern lagg vegetation most probably represents the latest stage in a secondary succession towards raised bog. The succession from wet fen to the modern vegetation appears to be an undisturbed record. This part of the sequence may represent a valuable analogue for the development of marginal pools and blocked former-cuttings on the present day peat surface. The depth of the hiatus in the Lagg2 record (110cm) suggests that the presumed peat cutting occurred several hundred years ago. This conclusion is supported by some preliminary observations of SCP concentrations in the upper peat. Most if not all of the industrial period appears to be represented within the upper three zones of Lagg2.Core Lagg5 provides a contrasting history of lagg development. On the banks of the Teifi fen conditions have prevailed throughout the time period represented by the core. Various Carex species, including Carex rostrata and Curta are present throughout the peat sequence. Other constant species include potentilla palsutris, Galium palustre and Eriophorum vaginatum. More detailed pollen and SCP analyses will be required to verify these findings prior to using the site for a high resolution reconstruction of vegetation development.In summary, the lagg fen on the banks of the Teifi may provide a valuable record of continuous lagg fen development, whereas the superficially similar lagg communities on the western margin of the West Bog have been significantly disturbed albeit several hundred years ago. The western lagg does provide a detailed and well preserved record of secondary lagg development after the abandonment of cuttings.<br/

A reappraisal of the mechanisms leading to ombrotrophy in British raised mires

Previous theories of raised mire initiation stress the role of autogenic processes aided by climatic forcing towards increased oceanicity. Recent evidence from stratigraphic surveys in Great Britain and Ireland, however, suggests that raised mire initiation can occur under conditions of falling or fluctuating water tables. Macrofossil assemblages from the lowermost raised peat strata can indicate repeated aeration of the newly formed peat surface. A previously unexplored mechanism for the fen-bog transition is discussed. New research is needed to assess its importance since a sound understanding of the way in which raised mires first formed is important for mire rehabilitation and conservation.<br/