Nitrogen Deposition

Effects and implications

• Increases in proportion of productive grasses at expense of fine leaved grasses.
• Reduces species richness, especially among forbs
• Possible reductions in productivity
• Changes in species composition
• Loss of rare or endangered species.
• Loss of annuals and forbs will have implications for sustainability, due to the short lived nature of the seed bank (Bossuyt et al 2005) and the isolation of many of these small areas of grassland.

Effects and implications

• Potential increase in graminoid (grass) biomass, with adverse effects on forbs.
• Loss of sensitive lichen species

Overview: evidence, processes and main impacts

This habitat represents a range of different systems for which there is no known experimental information on the impacts of nitrogen deposition.

Effects and implications

Since improved grasslands receive very high doses of Nitrogen in fertilisers and manures negative effects of atmospheric N deposition are not expected. In this case the atmospheric Nitrogen inputs could be considered as beneficial, providing a small additional source of 'fertiliser'.

Effects and implications

• Sphagnum species will be vulnerable to N both through direct N induced toxicity and indirectly from shading by increased vascular plants growth. The extent to which shading occurs will reflect the capacity of the vascular plants to use the addition N to increase C assimilation. Molinia caerulea , despite having a relatively low Ellenberg N score  appears to be a nitrophile in the presence of high NH₄⁺ concentrations (van den Berg pers comm.).