Wet grassland and rush pasture

Overall vulnerability

Feature assessed:

• Wet grassland and rush pasture

Special qualities:

• Beautiful views created by contrasting landscapes and dramatic geology
• Internationally important and locally distinctive wildlife and habitats

Feature description:

The habitats considered for this assessment fall into two main categories. Firstly, areas of moorland dominated by purple moor-grass – often blanket bog or heath which has been invaded as a result of regular burning over wet soils. Much less extensive however is rush pasture. Occurring on wet and infertile soils, it contains a mixture of grasses (including purple moor-grass), sedges, rushes and also some broadleaved species. Wet grassland and rush pasture covers approximately 1,550 hectares in the PDNP, 250 ha of this being priority habitat. They can be important habitats for many invertebrate species, and also several species assessed in this report (see short-eared owl, curlew, snipe and lapwing).

How vulnerable is wet grassland and rush pasture?

Wet grassland and rush pasture in the PDNP have been rated ‘high’ on our vulnerability scale. This score is due to high sensitivity and exposure to climate change variables, the fragmented nature of the more rare and biodiverse rush-pasture type habitats, coupled with a moderate adaptive capacity.

Mismanagement and drainage has resulted in many areas of wet grassland becoming species poor, some being dominated by purple moor-grass. The reliance of these grasslands on water input coupled with the economically uncertain nature of upland farming mean that climate changes have the potential for large direct and indirect impacts.

However, through environmentally sensitive management and restoration of water tables it should be possible to partially offset some of these impacts. The key adaptation measures are to join up and enhance remaining fragments of rush pasture where it is possible to maintain or increase water levels; and to accept that some areas may need to be converted to other habitat types such as flower rich meadows. The diversification of the sward in purple moor-grass dominated blanket bogs through the reintroduction of Sphagnum mosses should increase the biodiversity and the future resilience of these wetlands.

Current condition:

Whereas purple moor-grass dominated moorland can be found in relatively large blocks, the remaining rush pastures in the PDNP are now fragmented, with loss being due to agricultural improvement such as drainage and application of fertilizer or inappropriate management such as overgrazing or abandonment. Where moorland habitats have been managed inappropriately, they have often become dominated by purple moor-grass to the exclusion of almost all other plant species.

What are the potential impacts of climate change?

Overall potential impact rating

Direct impacts of climate change

These habitats are sensitive to changes in soil moisture, so there is a potential for shifting patterns of precipitation and changes in temperature to have a significant effect. Increased spring soil moisture levels coupled with higher temperatures could lead to an increase in vegetation biomass, which in turn could lead to changes in human behaviour such as altering livestock levels. Increased stocking can lead to detrimental effects such as soil poaching, increasing dominance of soft rush and other stress tolerant plants. Data Certainty: High Early growing species may begin to dominate the plant communities, while later flowering plants such as devil’s bit scabious may be reduced. Data Certainty: Low

Similarly, drier summers and drought periods may lead to drier soils and a change in habitat composition, such as a move toward acid or species-poor neutral grassland. Richer rush pastures may become less diverse with a resultant impact upon invertebrates and their predators. Breeding waders are likely to be impacted by a reduction in the availability of invertebrates. This may also affect thrush species such as ring ouzel during the spring and summer, and autumn migrants such as redwing and fieldfare later in the year. Data Certainty: High Conversely, increased waterlogging due to wetter winters and increased periods of flooding could lead to colonisation by ruderal species such as soft rush and ultimately a change towards species better able to cope with inundation. Data Certainty: High Increased atmospheric carbon dioxide may affect the soil chemistry and productivity of plants and therefore change interspecific competition, potentially leading to the loss of the less competitive species. Data Certainty: Low

Human behaviour change

Hotter, drier summers resulting in drier ground conditions may enable changes to the way rush pastures are farmed. The altitude of land suitable for in-bye may increase, and it is possible that some areas will become suitable for easier drainage, more intensive grazing regimes or even arable use. This could lead to a loss of habitat for invertebrates and feeding opportunities for birds - particularly waders. Data Certainty: High Due to drier ground conditions, purple moor-grass dominated moorlands may also be more susceptible to damage from wildfire, the human ignition sources of which may also increase. However, wildfire on purple moor-grass dominated moorland is more likely during spring when the deciduous leaf blades are dead and dry. Prolonged drought is less likely earlier in the year, and the wet nature of this habitat likely reduces this risk significantly. Data Certainty: Low

Wetter winters may lead to stock exclusion during winter and spring if land becomes too saturated or waterlogged to either graze or access Data Certainty: High leading to abandonment of certain areas as pasture. A longer sward in the spring may disadvantage ground nesting birds such as lapwing. However, reduction of soil compaction during wetter periods could be benefit soil invertebrates and have knock on effects on their predators.

Invasive or other species interactions

Increases in severity and frequency of flooding events in summer and winter may lead to increased disturbance of ground cover and therefore opportunities for invasive species to spread. While wet grasslands are currently not particularly prone to invasion, climate change may mean species such as Himalayan balsam are able to dominate in some areas. Data Certainty: Moderate Changes in carbon to nitrogen ratios in plant leaves may enhance their nutritional value resulting in an increase in herbivory. Data Certainty: High

Nutrient changes or environmental contamination

Wetter winters and flooding events may lead to nutrient loading of some sites, depending on surrounding land use and topography. This may mean that vegetation types adapted for low nutrient input are impacted and species composition may change. Data Certainty: Moderate

What is the adaptive capacity of wet grassland and rush pasture?

Overall adaptive capacity rating

Both types of wet grassland covered here require some form of active management, so it is possible to vary their management – for example by ensuring a more appropriate or flexible grazing regime - in order to ensure they are as resilient to climate change as possible. In the case of rush pastures this could involve ensuring that low intensity grazing or appropriate cutting is implemented, whereas in the case of purple-moor grass dominated moors this may involve the diversification of the sward and species in an attempt to move towards a more heterogeneous habitat.

Purple-moor grass dominated moors cover large continuous areas, whereas rush pastures in the PDNP cover a much smaller area and are more fragmented. The remaining fragments and the species they support are less likely to be adaptable to climate change, and are unlikely to adapt well to a severe decrease in wetness. However, these habitat types can occur on a wide range of soils ranging from acid to alkaline and there is a good potential for wet grassland habitat creation alongside restoration and sensitive management of existing areas.

Environmental stewardship options are currently available for the maintenance and restoration of wet grassland and within the PDNP there are several organisations which have the potential to help landowners to drive forward suitable adaptive measures including the PDNP Partnerships (Moors for the Future Partnership and South West Peak Partnership), and Non-Governmental Organisations (NGOs) such as National Trust and RSPB. There is potential for some of these areas to become the focus of Natural Flood Management schemes and thereby attract future funding not directly related to food production. By managing grazing levels, restoring water tables and joining up rush pasture fragments it should be possible to at offset some of the impacts of climate change.

Key adaptation recommendations for wet grassland and rush pasture:

Improve current condition to increase resilience

The current condition of a feature is an important factor alongside its sensitivity and exposure, in determining its vulnerability to climate change. These recommendations are aimed at improving the condition of the feature at present, therefore making it better able to withstand future changes to climate.

• Ensure appropriate levels of grazing are maintained.
• Increase connectedness, size and condition of rush pasture through habitat creation and restoration of adjoining semi-improved grasslands.
• Retain wetness by blocking artificial drainage.
• Re-introduce Sphagnum to sites where purple-moor grass has invaded blanket bog.
• Consider the impact on key views when planning adaptations. Improve current condition to increase resilience: Targeted conservation efforts for important sites and at risk areas

The current condition of a feature is an important factor alongside its sensitivity and exposure, in determining its vulnerability to climate change. These recommendations are conservation measures aimed at those sites that will have the biggest impact for this feature – either because they are particularly important for the feature or because they are most at risk from climate change.

• On sites of importance for breeding waders where it is not viable to maintain water levels across the whole site, consider minor channelling of the water resource to retain some wet flushes.

Improve current condition to increase resilience: Increase structural diversity to improve resilience at a landscape scale

The current condition of a feature is an important factor alongside its sensitivity and exposure, in determining its vulnerability to climate change. These recommendations focus on increasing the structural diversity of the area or habitat in which the feature is found. This can help to offset the effects of climate change on the feature, as well as to allow it to be in a better position to recover from future climate changes.

• Increase the variation in vegetation structure across site to maximize biodiversity. Rush management should be planned with the needs of different species in mind.
• If it is not possible to maintain wetness of rush pasture accept that it will change and facilitate conversion to other priority habitats such as species rich meadow.

Adapt land use for future conditions

These recommendations are adaptations to the way in which people use the land. Flexibility in land management - reacting to or pre-empting changes caused by the future climate - should afford this feature a better chance of persisting.

• Flexibility in grazing is key – changing timings and providing alternative land for years where areas are flooded could be important to limit land abandonment on economically marginal land.
• Altering livestock may have benefits for the pasture habitats. Native grazer analogues such as appropriate cattle breeds that are less selective than sheep are more likely to facilitate a diverse sward.