Expansion of invasive species on ombrotrophic bogs: desiccation or high N deposition?

H.B.M. Tomassen, A.J.P. Smolders, J. Limpens, L.P.M. Lamers, J.G.M. Roelofs

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156 Citations (Scopus)


1. In many ombrotrophic bog areas the invasion of grass (e.g. Molinia caerulea) and tree (e.g. Betula pubescens) species has become a major problem. We investigated whether the invasion of such species is due to high atmospheric nitrogen (N) deposition by conducting a fertilization experiment. 2. The effects of experimentally increased N input on Molinia, Betula and Eriophorum vaginatum were studied in desiccated bog vegetation in Ireland, where there is relatively low background N deposition. Four different N treatments were applied for 3 years: 0 (control), 2, 4 and 8 g m-2 year-1. 3. Ammonium and nitrate concentrations in the peat moisture increased at high N addition rates, leading to significantly higher carbon : nitrogen (C : N) and nitrogen : phosphorus (N : P) ratios in the top layer of the peat. The potential CO2 production rate of the peat was not stimulated at high N addition rates due to severe acidification of the peat. 4. Despite high tissue N : P ratios (above 40), above-ground biomass production by Molinia was stimulated at high N addition rates, and foliar nutrient concentrations were unaffected. In contrast to Molinia, Betula and Eriophorum were unable to increase their above-ground biomass, probably due to P limitation. Regrowth of the lichen Cladonia portentosa was suppressed at high N addition rates. 5. Synthesis and applications. We conclude that the invasion of bogs by Molinia and Betula is likely to be less affected by desiccation than by increased N availability. Apparently, Molinia is well adapted to P-limiting conditions, which may explain its success in regions with increased N deposition levels. The high availability of P in many Dutch bogs compared with Irish bogs, together with prolonged high N deposition levels, may explain the strong increase in both Molinia and Betula observed in the Netherlands. As long as N and P availabilities in Dutch bogs are too high to prevent invasion of Betula and/or Molinia, management measures stimulating growth of Sphagnum mosses could probably reduce the negative effects of high N deposition levels.
Original languageEnglish
Pages (from-to)139-150
JournalJournal of Applied Ecology
Issue number1
Publication statusPublished - 2004


  • bogs
  • invasions
  • plants
  • nitrogen
  • desiccation
  • peat soils
  • air pollution
  • phosphorus
  • drainage
  • betula pubescens
  • cladonia
  • molinia caerulea
  • sphagnum
  • netherlands
  • irish republic
  • atmospheric nitrogen deposition
  • caerulea l moench
  • vulgaris l hull
  • calluna-vulgaris
  • molinia-caerulea
  • nutrient availability
  • cladonia-portentosa
  • vascular plants
  • growth


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