Expansion of invasive species on ombrotrophic bogs: desiccation or high N deposition?
Article first published online: 12 FEB 2004
Journal of Applied Ecology
Volume 41, Issue 1, pages 139–150, February 2004
How to Cite
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 Ecology, 41: 139–150. doi: 10.1111/j.1365-2664.2004.00870.x
- Issue published online: 12 FEB 2004
- Article first published online: 12 FEB 2004
- Received 29 December 2002; final copy received 23 September 2003
- Betula pubescens;
- Cladonia portentosa;
- Molinia caerulea;
- nitrogen deposition;
- phosphorus limitation;
- 1In 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.
- 2The 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.
- 3Ammonium 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.
- 4Despite 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.
- 5Synthesis 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.