Summary • Description • Constraints • Potential effects • Monitoring • Locations • Further information

Case Studies	Aberlady, East Lothian
	Bridgewater Bay, Somerset

Summary

Grazing management is by far the most common form of saltmarsh management undertaken in the UK. However, its use is restricted to improving the nature conservation interest of a marsh rather than performing any specific saltmarsh protection function. Marshes that have not been previously intensively grazed are usually more diverse than those which have experienced it in the past. However, such sites are uncommon and most marshes in the UK have experienced some form of grazing pressure for mainly agricultural purposes.

Continued grazing of such marshes is generally preferred as, once disturbed, formerly grazed marshes do not regenerate into the previously rich and diverse marsh community that existed prior to grazing. Rather, they develop into a sward dominated by a few grazing/trampling tolerant species, the growth of which can be mutually exclusive to other plants, such that recolinisation by other saltmarsh species at any stage in the succession is prevented.

Description

The use of grazing animals as a tool for managing the nature conservation interest of a saltmarsh is well documented (Chatters, 2004; Paterson & Burrows, 1998). In terms of grazing management, three types of saltmarsh are generally recognised; ungrazed saltmarsh, grazed saltmarsh and formerly grazed saltmarsh (recognising that marshes that have experienced livestock grazing in the recent past are generally encouraged to maintain a degree of grazing rather than grazing being abandoned altogether).

Click here for a more detailed discussion on the effects of grazing.

The adoption of a particular grazing regime will be dependant on the nature conservation objectives for the marsh, as different species of plant, invertebrates or birds will favour specific saltmarsh assemblages over others. Once these objectives are defined the selection of a suitable grazing regime will normally fall into one of three categories:

Lightly grazed

Grazing by native herbivores, such as ducks or geese, and/or low levels of intermittent grazing by livestock (typically at a ratio of 2 to 3 sheep or 0.7 to 1.0 young cattle per hectare, between April and October (Beeftink, 1977). This level of grazing is probably replicates most closely the ‘natural’ ungrazed system, typically proving good structural diversity and a wide range of species of plants and invertebrates, plus grazing intolerant species.

Moderately grazed

Livestock grazing at typical densities of 5 to 6 sheep or 1 to 1.5 young cattle per hectare between April and October (Beeftink, 1977). This level of grazing produces an ‘intermediate’ conservation value and the communities that result are very dependant on the type of grazers used (e.g. cattle tend to produce a more structurally diverse vegetation than sheep).

Heavily grazed

In terms of nature conservation, this is the least preferred option. Grazing levels are typically 9 to 10 sheep or 2 to 2.5 young cattle per hectare, again, between April and October (Beeftink, 1977). These stocking densities really only apply to the agricultural sector rather than saltmarsh management, as the botanical and invertebrate biodiversity achieved is low. In addition, breeding birds nests can be affected through trampling.

An ideal situation would be to aim for a range of grazing pressures, and thus sward heights, across a site. This would enable a range of species adapted to specific niches to co-exist along with other species suited to a different level of grazing pressure (Lambert, 2000). However, in practice, this is very difficult to achieve as most sites experience a conflict of management requirements. Fortunately, there is a natural tendency for a range of sward types to develop, as grazing can be quite localised, e.g. at access or watering points. There then should be a reduction in grazing pressure away from these areas towards the periphery of the marsh, with a corresponding change in sward heights. However, this is easier to achieve on large rather than small sites and on more deeply dissected marshes than on ones with few drainage channels (Lambert, 2000).

 Another method of grazing management involves the rotation of livestock across the saltmarsh and/or adjoining areas and throughout the year. A grazing regime in a specific area for a specific length of time promotes localised disturbance and allows plants with high growth rates and low growth forms to colonise. After grazing has ceased for the year (e.g. cattle mainly graze April to October), or has moved on to another area, the saltmarsh has time to regenerate, potentially increasing sward height which, in turn, can lead to an increase in sediment accretion.

Constraints

The above stocking densities are indicative only, as each site will vary in terms of existing environmental conditions and historical grazing regimes. Furthermore, determining stock densities may be difficult if the livestock have access to other areas, e.g. adjacent farmland.

Grazing across a marsh can be very localised, decreasing significantly from the sea wall, where pressure is greatest, to the pioneer zone which may be largely unaffected (Patterson & Burrows, 1998).

Potential effects

A range of impacts can be associated with grazing. The main effects are (summarised from Chatters, 2004):

• The process of sedimentation is reduced;
• With high stocking rates, species richness can decrease;
• Species and plant communities of the lower saltmarsh can spread into the higher saltmarsh;
• Different vegetation patterns develop, especially in association with low stocking density;
• Litter production and population density of detritus-feeding invertebrates and their predators decrease;
• Immigration of invertebrates from higher saltmarshes into lower saltmarshes is reduced;
• The invertebrate community of lower saltmarshes spreads into higher saltmarshes;
• The number of plant-feeding insect species can decreases as a result of the destruction of the higher vegetation canopy;
• The surface roughness of marshes can reduce and, hence, their sea defence value; and
• Improved habitat for grazing wildfowl, such as Wigeon, can be created.

Monitoring

Monitoring requirements will depend on the purpose of the grazing regime. If the purpose is to improve habitat for breeding birds or overwintering wildfowl, then bird counts before and after using British Trust for Ornithology (BTO) survey methods will need to be carried out. Similarly, if the purpose is to increase terrestrial invertebrate diversity and/or plant diversity then post and pre-grazing surveys using established techniques (e.g. NVC surveys) should be undertaken.

If the desired objectives are not being met, then some consideration should be given to changing the stocking density.

Locations

Grazing management is undertaken at various locations in the North West (e.g. Morecambe Bay and associated Estuaries), on the Humber Estuary and at Orford Ness (by the National Trust).

Further information

Beeftink, W.G. (1977). Saltmarshes. In: The Coastline, Barnes (ed.), R.S.K. John Wiley & Sons, Chichester , 93-122.

Chatters, C. (2004). Grazing domestic animals on British saltmarshes. British Wildlife. Vol. 15 No.6 pp392 -400.

Lambert, R. (2000). Practical management of grazed saltmarshes. In: British Saltmarshes. Sherwood, B.R., Gardiner, B.G. & Harris, T. (eds.). Linnaean Society of London, pp333 -339.

Packham, J.R. & Willis, A.J. (1997). Ecology of Dunes, Saltmarsh and Shingle. Chapman & Hall, London . 335pp

Patterson, I. & Burrows, A. (1998). Grazing the Wash. Enact 6 Vol. 1. pp 15-17.