Long term effects of enhanced nitrogen deposition on a lowland dry heath in southern Britain
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Experimental additions of ammonium sulphate to a nitrogen-poor dry heathland have been carried out since 1989. There are four nitrogen treatments: a control (receiving artificial rain only), a low treatment which receives an additional 7.7 kg N ha−1 yr−1, a high treatment receiving 15.4 kg N ha−1 yr−1 and an alternating treatment which receives either the control or the high nitrogen additions, in alternate years. The estimated background deposition at the study site is 13–18 kg N ha−1 yr−1, a value similar to the critical load that has been suggested for the conversion of lowland heath to grassland. Over the past 5 years there have been significant stimulations in shoot growth, flowering, canopy density and litter production. Flowering, in particular, strongly reflects nitrogen additions in the alternating treatment.
Current models of the response of dry Calluna heathlaud to enhanced nitrogen deposition suggest that higher tissue nitrogen levels will occur and will be accompanied by heightened sensitivity to secondary stresses. This may in turn lead to canopy breakdown and replacement by grassland. The application of nitrogen at deposition rates only slightly in excess of the critical load over five years has produced small, non-significant increases in shoot nitrogen content. However, there is clear evidence of a large positive effect on shoot growth, flowering, litter production and canopy density of Calluna. The observation of these responses at the application rates used in this study supports the current proposals for critical loads of nitrogen for lowland heaths.
Key wordsnitrogen heathland Calluna vulgaris critical load growth litter production
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- Aerts, R.: 1989, Oecologia 78, 115–120.Google Scholar
- Allen, S. E.: 1989, Chemical analysis of ecological materials, Blackwell Scientific Publications, Oxford.Google Scholar
- ApSimon, H.M., Kruse, M. & Bell, J.N.B.: 1987, Atmos. Environ. 21 (9), 1939–1946.Google Scholar
- Berendse, F.:1990,J. Ecol. 78, 413–427.Google Scholar
- Bobbink, R., Boxman, D., Fremsted, E, Heil, G.W., Houdijk, A. & Roelofs, J.: 1992, Nord (Miljörapport) 41, 115–119.Google Scholar
- Brunsting, A.H.M. & Heil, G.W.: 1985, Oikos 44, 23–26.Google Scholar
- Bunce, R.G.H. (Ed.): 1989, ITE research Publication No. 3, HMSO, London.Google Scholar
- Caporn, S. J.M., Caroll, J., Lei, Y., Song, W., Read, D.J. & Lee, J.A.: 1995, In: Acid Rain and its Impact: The Critical Loads Debate (Ed. R.W. Battarbee), Ensis Publishing, London, 146–150.Google Scholar
- Gimingham, C.H.: 1972, Ecology of heathlands, Chapman & Hall, London.Google Scholar
- Heil, G.W. & Bruggink, M.: 1987, Oecologia 73, 105–108.Google Scholar
- INDITE: 1994, Jimpacts of Nitrogen on Terrestrial Ecosystems, Department of the Environment, London.Google Scholar
- Marrs, R.H.: 1993, Biol. Conserv. 65, 133–139.Google Scholar
- McCullogh, P. & Nelder, J.A.: 1983, Generalised Linear Models, Chapman & Hall, London.Google Scholar
- Pitcairn, C.R.E., Fowler, D. & Grace, J.: 1995, Environ. Pollut. 88 (2), 193–205.Google Scholar
- Prins, A.H., Berdowski, J.J.M. & Latuhihin, M.J.: 1991, Acta Bot. Neerl. 40 (4), 269–279.Google Scholar
- Sokal,R. &, Rohlf, F.J.: 1995, Biometry, W.H.Freeman & Company, New York.Google Scholar
- Uren, S. C.: 1992, PhD Thesis, University of London.Google Scholar
- Van der Eerden, L. J., Dueck, Th. A., Berdowski, J.M., Greven, H. & Van Dobben, H.F.: 1991, Acta Bot. Neerl. 4, 281–296.Google Scholar