Saltmarsh
Saltmarsh supports a host of specially adapted species that can tolerate the salt-rich landscape which is regularly covered by the tide, including plants, invertebrates and fish.
Saltmarsh is one of the most important habitats for breeding Redshank in the UK.
What
Saltmarshes are coastal wetlands, made up of a complex web of creeks and pools, which fill and drain on the incoming and outgoing tides. Made of boggy soils and peat, they are dominated by salt-tolerant species of flora which form one of the world’s rarest habitats, and which supports a host of specially-adapted species of fauna. They generally form in estuaries, or other sheltered areas, where coastal process allow for the deposition and accretion of sediment.
Why
The UK supports a significant percentage of Europe’s saltmarsh, which in turn supports half of the British breeding population of Redshank. However, breeding Redshank are in steep decline, with the loss of more than half the population since the 1980s, despite the overall area of saltmarsh in the UK increasing. Inappropriate grazing management is understood to be one of the main driving forces behind this decline.
Not only are saltmarshes important for breeding Redshank, amongst other birds, but they also host a number of other rare plants and insects such as Sea Aster Mining-bee and the Scarce Pug moth supported by plants like Sea Aster, Sea Wormwood and Sea Lavenders. The habitat also provides nurseries for spawning fish and important feeding areas for migrating birds.
Saltmarshes are excellent carbon stores, holding up to three times as much carbon as forests, and help with flood prevention by reducing wave action and protecting flood defences. However, they are under threat from coastal squeeze; as sea levels rise, larger areas of saltmarsh will be permanently underwater, completely changing their ecological make-up. Under natural conditions, saltmarshes would simply retreat further inland, but manmade structures such as sea defences will, in many parts of coastal Britain, prevent this from happening.
Therefore, as more and more of our saltmarshes become unsuitable for wildlife through sea-level rise, we need to ensure that those that remain suitable are managed in the best possible way.
How
Due to the remote and often inaccessible nature of saltmarshes in the UK, they are traditionally managed with livestock grazing. Managing grazing at the right levels, with the right livestock and at the right time of year is however crucial to ensuring the habitat is the best condition for saltmarsh specialist birds, invertebrates and plants.
Grazing
Although much of the UK’s saltmarsh is grazed, management practices vary greatly, and how biodiversity is faring on these areas will also vary too. Therefore, it is recommended that site-specific monitoring of breeding birds and vegetation occurs to assess the condition of these features before management practices are changed.
However, there are some general rules around grazing of saltmarsh that apply to all areas and should be considered when grazing animals are present:
Vegetation structure and plant species diversity
- Breeding Redshank require a mixed sward structure which includes tussocks or patches of longer vegetation (see figure below) and grazing should be tailored to create this structure. They cannot nest on saltmarsh where the vegetation is too long or too short. Many saltmarsh invertebrates are also benefitted by varied sward structures. Mixed sward structures are most reliably produced using low stocking rates of less than or equal to 0.3 Livestock Units per hectare (equivalent to 3 cattle or 25 sheep per 10 hectares).
- Cattle produce much more variable sward structures than sheep because of the grazing behaviours of the different livestock types. Cattle rip mouthfuls of grass from the saltmarsh and avoid grazing around their own droppings which creates patches of longer sward, while sheep nibble and bite indeterminately which results in a more uniform sward of short, cropped vegetation. Sheep are also more likely than cattle to eat the flowers of plants which can reduce flowering plant and invertebrate species abundance. Cattle grazing is therefore better for conservation grazing management on saltmarsh.
- Grazing can also negatively impact on highly palatable saltmarsh plants such as Sea Aster with negative consequences for specialist invertebrates which rely on this plant.
- Saltmarshes that are already floristically rich with a good variable vegetation structure and are currently ungrazed by livestock are unlikely to benefit from the introduction of livestock grazing.
Nest trampling and grazing timings
- Redshank nests are placed on the ground and are extremely vulnerable to trampling, and thus measures should be taken to reduce or remove the risk of this happening during the breeding season.
- The traditional timing of grazing (April–October) and the timing of Redshank nesting (April–June) overlaps, as does the area of the saltmarsh which livestock use and the area where Redshank nest.
- GPS-tracking studies have demonstrated that cattle grazing on saltmarsh congregate in ‘upper’ and ‘mid’ zonal areas of the marsh which are close to the land, usually within 500m of the sea wall or bank, and remain in this area through the spring and summer before grazing here is exhausted and the cattle are forced to graze further out. This leads to heavier grazing in this smaller area of saltmarsh. This heavier grazing in these ‘upper’ and ‘mid’ marsh zones brings livestock into direct conflict with Redshank, which nest in the same areas of the saltmarsh at the same time of year, leading to higher rates of nest trampling even at low stocking rates.
- Keeping experienced animals in the herd and moving freshwater supplies further out on to the marsh can help reduce these impacts, but ideally livestock grazing would be delayed until July. This is not always achievable, so there are three options that could be explored to reduce Redshank nest trampling while maintaining optimal sward and habitat conditions:
- Delay the onset of grazing. Most Redshank nests will hatch by the end of June, at which point higher grazing intensities, up to 0.7 LU/ha, can be introduced.
- Reduce the number of grazing livestock in the spring and early summer. Grazing rates must be very low to ensure a reduction in trampling, at 0.1 livestock units per hectare (LU/ha) between April and June. These could then be increased to 0.7 LU/ha from July to October.
- Introduce rotational grazing. Grazing on a rotational basis means some areas of saltmarsh can be left ungrazed in which Redshank can nest without risk of trampling. These areas should be left for 1-2 years at most to prevent the development of rank grasses and a reduction in plant species diversity.
More information
For more information, it is recommended you contact your local statutory agency adviser and RSPB Conservation Officer.
In practice
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