Threats to UK Lowland Grassland Habitats

 

Unimproved culm grassland grazed by Devon cattle, Whiteleigh Meadows © Robert WoltonUK lowland grassland habitats and their associated species are threatened by a range of factors.Most grassland in the UK has undergone agricultural improvement through ploughing and re-sowing, heavy inputs of fertilisers, and intensive cutting or grazing. This remains an important threat, as does over-grazing or cutting at the wrong time of year. Increasingly, grasslands are also threatened by under-management or abandonment of traditional grazing or cutting. Conservation action and planning policies have reduced some of these threats, but agricultural intensification and abandonment, as well as loss to urban development, remain as serious issues. Less tangible threats are posed by habitat fragmentation and isolation, atmospheric nitrogen deposition and climate change.

 

The table below provides a summary of major pressures and threats to UK lowland grassland habitats – details are given beneath. These are based on information in the 3rd UK Report on Implementation of the Habitats Directive, the UK Biodiversity Habitat Action Plans, and Common Standards Monitoring for Designated Sites: First Six Year Report.

 

UK BAP priority habitat

Modification of agricultural practices

Fragmentation

Air pollution

Under-management

Development

Water management & quality

Land reclamation & mineral re-working

Lowland meadows

*

*

*

*

*

*

 

Purple moor grass and rush pastures

*

*

*

*

*

*

 

Lowland dry acid grassland

*

*

*

*

*

 

 

Lowland calcareous grassland

*

*

*

*

*

 

 

Calaminarian grassland

*

*

*

*

 

 

*

Upland hay meadows

*

*

*

 

 

 

 

 

Under-management

Scrub Sites need a minimal level of grazing and/or hay-cropping, which in some cases is not achieved. For flood meadows and purple moor-grass and rush pastures, management by cutting and/or grazing may need to be increased if the water which inundates them contains high levels of nutrients. Under-management is largely due to current agricultural economics and policies, exacerbated by stock regulations and restrictions. Some farmers are reluctant to keep stock (large stock in particular) on pasture perceived to have little nutritional value. The consequent lack of management such as cutting, grazing or flooding will lead to colonisation by shrubs and trees which over-top the grasses and herbs and develop into scrub and woodland. On some grasslands, bracken encroachment is a common result, sometimes together with invasive species problems. Calaminarian grasslands require more or less continuous grazing by rabbits or sheep, without which soil organic material builds up, with a gradual dilution of the effect of heavy metal contaminants, often resulting in scrub invasion. In this case some form of disturbance may be necessary to maintain soil toxicity.

 

Agriculturally improved, species-poor grassland cut for silage © Neil Matson, ACT Ltd

Modification of agricultural practices

This includes draining, cultivation and fertilising as well as inappropriate cutting/grazing and has resulted in an overall loss of grassland biodiversity through loss of species number and abundance. The practice of cutting grass early for silage rather than hay reduces seeding by flowering plants and destroys the nests of characteristic birds. For some grasslands, the timing of spring shut-up date is also thought to be important, particularly upland hay meadows. Improvement of grassland, usually done by re-seeding and fertilizing, drainage and stock feeding, reduces sward species diversity as well as habitat diversity over a wider area. Inappropriate grazing can also lead to a build-up of nutrients. The application of herbicides can also be a direct cause of species loss.

 

Fragmentation

fields surrounded by industrial and urban development, Carmarthenshire © COWI-Vexcel

Many grassland habitats have existed in a fragmented state for many centuries, so fragmentation per se should not be seen simply as unfavourable. However, in some places fragmentation is extreme and it occurs only in very small, isolated patches and fragmentation is thus an issue of great concern for this habitat. It may prove to be a threat to the sustainability of many species populations, as well as causing management problems. Some semi-natural lowland grassland sites may be too small to be considered viable. Habitat fragmentation and isolation also reduce the ability of species to respond to climatic change because there is less potential for a species to colonise (migrate) from distant sites.

 

Air Pollution

Based on an assessment of the exceedence of relevant critical loads, air pollution is considered to be a potentially significant pressure to the structure and function of most lowland semi-natural grassland habitats. Atmospheric nitrogen deposition is a particular concern as it is considered to be a key threat for most semi-natural grassland types. For further info: UK Air Pollution Information System (APIS).

 

Lowland grassland covered by winter flooding, Derwent Ings, Yorkshire © Richard Jefferson NEWater management and quality

For wet grasslands, the management of surface and groundwater is clearly crucial to providing the appropriate surface:groundwater conditions, for example, flood meadows require seasonal inundation. The constituents of the water are also important, for example the basic ions such as calcium, its pH, and quantity of the plant nutrients nitrogen and phosphorus.

 

Development

Although of lesser concern than the above agricultural changes, some sites are still being lost to industrial development, housing and infrastructure.

 

Mineral re-working and land reclamation

For Calaminarian grassland, the re-working of abandoned mineral veins can be a significant threat to some sites. At other sites, grassland is deliberately ‘reclaimed’ to remove a source of contamination to livestock or simply to improve the aesthetic appearance of former mining land.