New Phytol. (1980) 85, 301-319 THE DEVELOPMENTAL HISTORY OF SCRAGH BOG, CO. WESTMEATH AND THE VEGETATIONAL HISTORY OF ITS HINTERLAND BY M. O'CONNELL* Department of Botany, University College, Dublin, Eire (Accepted 26 September 1979) SUMMARY 301 Stratigraphical, macrofossil and pollen analytical studies on the sediments of Scragh Bog, a small fen in central Ireland, are described. The Flandrian pollen diagram is divided into local pollen assemblage zones which in turn are related to the zones of Mitchell (1956). The Ulmus-Quercus-Alnus assemblage zone of the Atlantic period is pr oposed as a regional assemblage for base-rich areas in Ireland as distinct from the Alnus-Quercus-Pinus regional assemblage of Jessen (1949). The changes associated with the Elm decline are considered in detail. The subfossil records, which are not abundant, include Acrocladium giganteum and Sphagnum contortum from the Late-glacial and Antitrichia curtipendula and lsothecium myosuroides, both probably from zone VIiia. The depositional processes in the basin and the vegetational history of the hinterland are reconstructed. The nature of Landnam and the possibility of in situ survival of the present-day fen communities are discussed. INTRODUCTION The researches of pollen and macrofossil analysts have established that fen com- munities similar to those that constitute the vegetation cover at Scragh Bog (O'Connell, in prep.) are found in subfossil form beneath the great expanses of raised bog that occur in Ireland and in parts of western and central Europe (Barry, Carey and Hammond, 1973; Barry and Synnott, 1970; Rybnicek, 1973). At approximately 7500 B.P., i.e. the Boreal/Atlantic transition (Hammond, 1968; Smith, Pearson and Pilcher, 1971 ; Rybnicek, op. cit. ), these minerotrophic fen communities were invaded by acidophile Sphagnum species which resulted in widespread initiation of ombro- trophic raised bog. This resulted in severe restriction of fen species generally and, in particular, of the bryophyte element which today has a decidedly Fenno-Scandinavian distribution. The purpose of the investigation reported here is to establish as far as possible, by pollen and macrofossil analyses, the successional events within the mire basin at Scragh Bog and in particular the manner of establishment and the factors which favoured the survival of the fen communities. Since a basin also acts as receptor of pollen originating in the surrounding countryside, a record is available of the vegeta- tional and environmental changes in the hinterland. This record, apart from its intrinsic interest, may be important in assessing the role of external factors in influenc- ing the direction and rate of change within the basin. • Now at: Department of Botany, University College, Gal way, Eire. 00 28-646X/80/060301 +21 $02.00/0 © 1980 The New Phytologist