VEGETATION AND ECOLOGY OF HUMMOCK-HOLLOW COMPLEXES ON AN IRISH RAISEDBOG

In this article the results of a study on hummock-hollow complexes on Clara bog (Co, Offaly, Ireland) are presented. The present size of the bog is the result of peat-cutting, road-building and drainage. These activities influenced the hydrology of the western side of the bog, wh ere the main flow of water is in a south-easterly direction. Specific distribution patterns of nutrients are found, with PO4(3-), NO2(-), NH 4+ NA+, K+, Ca2+, Mg2+, Mn2+, Fe3+, Al3+, Zn2+ and Pb2+ having low con centrations in the centre of the bog and higher ones towards the edges ; only SO4(2-) shows a reverse pattern. General descriptions of three ombrotrophic and seven minerotrophic vegetation types are given. Hummo ck-hollow complexes are found on plateaus on the bog where water flow is reduced. A transect study of hummock-hollow complexes revealed that the distribution of Sphagnum species is best explained by the height of the moss surface above the water-table. Other important ecofactors are the concentrations of Ca2+, Mn2+ and PO4(3-). Since the hydraulic conductivity is high in the acrotelm, the water-table acts as a plane below the microtopographical elements. Ecotope breadth and overlap cal culations for height above the water-table showed that both extremes o f the gradient are occupied by specialists while the slope is occupied by generalists. Similar calculations for PO4(3-), Mn2+ and Ca2+ showe d that Sphagnum species did not compete for them. This suggests that t hese ecofactors are dependent on the physical and chemical properties of the hummock-hollow structure. Analysis of nutrient concentrations i n Sphagnum plants showed that the relative composition reflects the su pply by wet deposition. The absolute amounts, however, are determined by the physiological properties of the individual species.