The modern floristic composition of the principal raised bogs of Wales is significantly altered compared with their histories of development from the early to mid Holocene. This paper uses pollen and plant macrofossil records from two raised bogs together with previously published data from a further two sites to explore the key factors contributing to the present condition of Welsh ombrotrophic plant communities. Results show Betula and Molinia invasion is a recent feature of bog development in Wales. Previous Holocene `dry-phases' were characterized by Ericaceae and Pinus establishment, supporting recent experimental evidence that Betula and Molinia encroachment is primarily a response to nitrogen (N) loading rather than desiccation on intact bogs. Several of the bogs featured in this study also show severe signs of structural damage, not only from peat cutting but, in the case of Cors Caron, from channel processes in the adjacent River Teifi. Radiocarbon dating and inter-site comparisons of peat accumulation rates show that Rhos Goch Common in particular has been heavily impacted by peripheral peat cutting, leading to dewatering, significant subsidence of its peat dome and the spread of hummock and high dry ridge communities. Finally, the decline and local extinction of Sphagnum austinii in bogs across Europe represents one of the most significant changes in ombrotrophic community composition in the late Holocene. Co-registered pollen and macrofossil evidence from Cors Caron demonstrates that increases in landuse intensity over the last 2000 years are temporally associated with reductions in the abundance of S. austinii and ultimately its local disappearance from the palaeoecological record.
Andersen, S.Th.1965: Mounting media and mounting techniques. In K ummel, B. and Raup, D. , editors, Handbook of paleontological techniques. Freeman and Co. , 587—98.
2.
—— 1979: Identification of wild grasses and cereal pollen. Danmarks Geologiske Undersogelse Årbog1978, 69—92.
3.
Barber, K.E.1976: History of the vegetation. In Chapman, S.B. , editor, Methods in plant ecology. Blackwell , 5—83.
4.
—— 1981: Peat stratigraphy and climatic change: a palaeoecological test of the theory of cyclic peat bog regeneration. Balkema .
—— 1993: Peatlands as scientific archives of past biodiversity . Biodiversity and Conservation2, 474—89 .
7.
Barber, K.E. , Chambers, F.M. , Maddy, D. , Stoneman, R.E. and Brew, J.S.1994: A sensitive high-resolution record of Late-Holocene climatic change from a raised bog in Northern England . The Holocene4, 198—205 .
8.
Bartley, D.D.1960a: Ecological studies on Rhosgoch Common, Radnorshire . Journal of Ecology48, 205—14 .
9.
—— 1960b: Rhosgoch Common, Radnorshire: stratigraphy and pollen analysis . New Phytologist59, 238—62 .
10.
Bennett, K.D. , Whittington, G. and Edwards, K.J.1994: Recent plant nomenclatural changes and pollen morphology in the British Isles . Quaternary Newsletter73, 1—6 .
11.
Bobbink, R. and Roelofs, J.G.M.1995: Nitrogen critical loads for natural and semi-natural ecosystems: the empirical approach . Water, Air and Soil Pollution85, 2413—18 .
12.
Chambers, F.M. , Mauquoy, D. , Pearson, F. , Daniell, J.R.G. , Gent, A. and Cook, C.2001: Recent vegetational change in Welsh blanket mires: a palaeoecological appraisal. Countryside Council for Wales (CCW) Contract Science Report No. 420.
13.
Daniels, R.E. and Eddy, A.1990: A handbook of European sphagna. Natural Environmental Research Council, HMSO , Second Impression.
14.
Davies, J.L.1994: The Roman period. In D avies, J.L. and Kirkby, D.P. , editors, Cardiganshire county history volume 1: from the earliest times to the coming of the Normans. University of Wales Press , 275—317.
15.
Davies, W.1815: General view of the agriculture and domestic economy of South Wales. MacMillan .
16.
Davies, W.H.1962: The Romans in Cardiganshire . Ceredigion14, 85—95 .
17.
Dickson, C.1988: Distinguishing cereal from wild grass pollen: some limitations . Circaea5, 67—71 .
18.
Duller, G.1995: Tröels-Smith plotting program (TSPP). Kingston University .
19.
Edwards, K.J.1989: The cereal pollen record and early agriculture. In M illes, A. , Williams, D. and Gardner, N. , editors, The beginnings of agriculture. BAR International Series 496, 113—35.
20.
Faegri, K. and Iversen, J.1989: Textbook of pollen analysis. John Wiley & Sons , 4th edition.
21.
Godwin, H. and Conway, V.M.1939: The ecology of a raised bog near Tregaron, Cardiganshire . Journal of Ecology27, 313—63 .
22.
Godwin, H. and Mitchell, G.F.1938: Stratigraphy and development of two raised bogs near Tregaron, Cardiganshire . New Phytologist37, 425—50 .
23.
Grant, M.E.1995: The dating and significance of Pinus Sylvestris macrofossil remains at Fenn's/Whixall Moss: palaeoecological and comparative modern analyses. Unpublished Ph.D. thesis, Keele University .
24.
Green, B.H.1968: Factors influencing the spatial and temporal distribution of Sphagnum imbricatum Hornsch. Ex Russ . In the British Isles . Journal of Ecology56, 47—58 .
25.
Grimm, E.C.1991: TILIA and TILIA.GRAPH. Illinois State Museum .
26.
Grosse-Brauckmann, G.1968: Einige ergebnisse einer vegetationskundlichen auswertung botanischer torfuntersuchungen besonders im Hinblick auf Sukzessionsfragen . Acta Botanica Neerlandica17, 59—69 .
27.
—— 1972: Uber pflanzliche makrofossilien mittel-Europaischer torfe. I. Gewegereste Krautiger pflanzen und ihre merkmale . Telma2, 19—55 .
28.
Headley, A.D. , Wheeler, B.D. and Baker, A.J.M.1992: The impact of man on the vegetation of Crymlyn Bog . In Bragg, O.M., Hulme, P.D., Ingram, H.A.P. and Robertson, R.A., editors, Peatland ecosystems and man: an impact assessment. Department ofBiological Sciences, 257—61 .
29.
Hughes, P.D.M.1997: The palaeoecology of the fen/bog transition during the early to mid-Holocene in Britain. Unpublished Ph.D. thesis, University of Southampton .
30.
Hughes, P.D.M. and Barber, K.E.2003: Mire development across the fen—bog transition on the Teifi floodplain at Tregaron Bog, Ceredigion, Wales, and a comparison with 13 other raised bogs . Journal of Ecology91, 253—64 .
31.
Hughes, P.D.M. and Dumanyne-Peaty, L.2002: Testing theories of mire development using multiple successions at Crymlyn Bog, West Glamorgan, South Wales, UK . Journal of Ecology90, 456—71 .
32.
Hughes, P.D.M. and Schulz, J.2001: The development of the Borth Bog (Cors Fochno) mire system and the submerged forst beds at Ynyslas. In W alker, M.J.C. and McCarroll, D. , editors, The Quaternary of West Wales field guide. Quaternary Research Association , 104—12.
33.
Hughes, P.D.M. , Mauquoy, D. , Barber, K.E. and Langdon, P.G.2000: Mire development pathways and palaeoclimatic records from a full Holocene peat archive at Walton Moss, Cumbria, England . The Holocene10, 465—79 .
34.
Katz, N.J. , Katz, S.V. and Skobeyeva, E.I.1977: Atlas of plant remains in peats. Nedra .
35.
Lamers, L.M.P. , Bobbink, R. and Roelofs, J.G.M.2000: Natural nitrogen filter fails in polluted raised bogs . Global Change Biology6, 583—86 .
36.
Langdon, P.G. and Barber, K.E.2005: The climate of Scotland over the last 5000 years inferred from multiproxy peatland records: inter-site correlations and regional variability. Journal ofQuaternary Science20, 549—66 .
37.
Mauquoy, D. and Barber, K.E.1999: Evidence for climatic deteriorations associated with the decline of Sphagnum imbricatum Hornsch. Ex Russ. in six ombrotrophic mires from Northern England and the Scottish Borders . The Holocene9, 423—37 . Meade, R.1983: A description of Crymlyn Bog from selected physical, chemical and botanical measurements . NCC , unpublished report.
38.
Moore, P.D. , Webb, J.A. and Collinson, M.E.1991: Pollen analysis. Blackwell Scientific Publications , 2nd edition.
39.
Moore-Colyer, R.J.1977: The enclosure and drainage of Cors Fochno (Borth Bog), 1813—1847 . Journal of the Ceredigion Antiquarian Society8, 181—92 .
40.
Nash-Williams, V.E.1969: The Roman frontier in Wales. University of Wales Press , 19—50.
41.
Pearsall, W.H.1956: Two blanket bogs in Sutherland . Journal of Ecology44, 493—516 .
42.
Piggot, C.D. and Piggot, M.E.1963: Late-glacial and post-glacial deposits at Malham, Yorkshire . New Phytologist62, 317—34 .
43.
Praglowski, J.1970: The effects of pre-treatment and the embedding media on the shape of pollen grains . Review of Palaeobotany and Palynology110, 203—208 .
44.
Reimer, P.J. , Baillie, M.G.L. , Bard, E. , Bayliss, A. , Beck, J.W. , Bertrand, C.J.H. , Blackwell, P.G. , Buck, C.E. , Burr, G.S. , Cutler, K.B. , Damon, P.E. , Edwards, R.L. , Fairbanks, R.G. , Friedrich, M. , Guilderson, T.P. , Hogg, A.G. , Hughen, K.A. , Kromer, B. , McCormac, F.G. , Manning, S.W. , Ramsey, C.B. , Reimer, R.W. , Remmele, S. , Southon, J.R. , Stuiver, M. , Talamo, S. , Taylor, F.W. , van der Plicht, J. and Weyhenmeyer, C.E.2004: IntCal04 terrestrial radiocarbon age calibration, 26—0 ka BP . Radiocarbon46, 1029—58 .
45.
Rodwell, J.S.1991: British plant communities volume 2: mires and heaths. Cambridge University Press .
46.
Schulz, J.2004: Late-Holocene mire development of the lowland raised bogs Cors Caron and Cors Fochno: a palaeoecological approach using high resolution macrofossil analysis. Unpublished Ph.D. thesis, University of Southampton .
47.
Smith, A.J.E.2004: The moss flora of Britain and Ireland. Cambridge University Press , edition II.
48.
Stace, J.1997: New flora of the British Isles. Cambridge University Press , edition II.
49.
Stoneman, R.E. , Barber, K.E. and Maddy, D.1993: Present and past ecology of Sphagnum imbricatum and its significance in raised peat-climate modelling . Quaternary Newsletter70, 14—22 .
50.
Thingsgaard, K.2002: Taxon delimitation and gentic similarities of the Sphagnum imbricatum complex, as revealed by enzyme electrophoresis . Journal of Bryology24, 3—15 .
51.
Tomassen, H.B.M. , Smolders, A.J.P. , Lamers, L.P.M. and Roelofs, J.G.M.2003: Stimulated growth of Betula pubescens and Molinia caerulea on ombrotrophic bogs: role of high levels of atmospheric nitrogen deposition . Journal of Ecology91, 357—70 .
52.
Tomassen, H.B.M. , Smolders, A.J.P. , Limpens, J. , Lamers, L.P.M. and Roelofs, J.G.M.2004: Expansion of invasive species on ombrotrophic bogs: desiccation or high N deposition?Journal of Applied Ecology41, 139—50 .
53.
Tröels-Smith, J.1955: Characterisation of unconsolidated sediments . Danmarks Geologiska Undersgelse IV, Raekke3, 1—73 . Van Geel, B. and Middeldorp, A.A.1988: Vegetational history of Carbury Bog (Co. Kildane, Ireland) during the last 850 years and a test of the temperature indicator value of the 2H/'H measurements of peat samples in relation to the historical sources and meteorological data . New Phytologist109, 377—92 .
54.
Walker, D. and Walker, P.M.1961: Stratigraphic evidence of regeneration in some Irish bogs . Journal of Ecology49, 169—85 .
55.
Wells, C. , Huckerby, E. and Hall, V.1997: Mid- and late-Holocene vegetation history and tephra studies at Fenton Cottage, Lancashire, U.K . Vegetation History and Archaeobotany6, 153—66 .
