Calcareous grasslands are defined as species-rich grasslands that occur on shallow lime-rich soil derived from Carboniferous chalk or limestone rocks. They were created when areas of woodland were cleared (NIEA, 2005).
- Site: <25% scrub or dwarf shrub cover
- Soil: Calcareous/alkaline soils, rich in calcium carbonate, low in nitrates & phosphates
- Main species: Calcicole plants
- UK: 40,000-50,000 ha
- NI: 2,000 ha
- In Northern Ireland calcareous grassland is species-rich, supports characteristic calcicole (lives in calcareous soils) plant species & have less than 25% scrub or dwarf shrub cover (NIEA, 2005).
- Calcareous grasslands form on lime-rich soils (pH>6.5) that are generally poor in other plant nutrients such as nitrates & phosphates.
- Within NI most examples of calcareous grassland occur at altitudes above 150 metres but a few are found at lower elevations.
- Calcareous grassland is usually fragmented as it tends to occur as part of a mosaic of other habitats that are managed as rough grazing for domestic livestock (UK BAP, 1999). Habitats included in the mosaic include bog, wet heath & acid grassland.
- Scrub habitats are often associated with calcareous grassland & can increase their biodiversity by providing shelter for invertebrates through the development of scrub edge conditions (NIEA, 2005).
- Many plant communities that are similar to those in the NVC of Great Britain are included in calcareous grassland of Northern Ireland. These include: CG9 Sesleria albicans – Galium sterneri, CG10 Festuca ovina – Agrostis capillaris – Thymus praecox, CG13 Dryas octopetala – Carex flacca heath & CG6 Avenula pubescens grassland.
- Dwarf shrubs & herbs which grow on acidic soils are often associated with calcareous grassland & form limestone heath (NIEA, 2005).
- Carboniferous limestone bedrock is the most widespread calcareous rock in the uplands of NI. Most of the calcareous grasslands have formed on soils derived from such bedrock, which support the CG9 Sesleria albicans – Galium sterneri community.
Current Status in UK & Northern Ireland
- Limited information exists on the status of calcareous grassland in the UK, but it is clear that it has suffered a large decline, due to changes in agricultural practices & management.
- The NICS (2007) showed that the area of calcareous grassland did not change between 1998 & 2009 in the UK.
- Calcareous grassland covers approximately 59,000 ha (approx. 0.2% of UK).
- Estimating the extent of calcareous grassland in NI is difficult as it is fragmented in County Antrim. Murray et al. (NICS, 1992) estimated that 1000 ha could be described as calcareous grassland but this is an underestimate as it only includes grassland on limestone, disregarding other substrates (NIEA, 2005). The NICS (2000) recorded a small decline in calcareous grassland between 1991 & 1998. The decline has mainly been attributed to scrub invasion & conversion to intensively managed grassland. Such decline may be detrimental to the resource in NI due to its limited distribution & slow recovery rate.
- The NICS (2007) reported that calcareous grassland covers an estimated 2000 ha in NI (0.1% of land area). County Fermanagh has the largest area (936 ha).
- Calcareous grasslands are threatened by overgrazing, quarrying, air pollution, climate change, habitat fragmentation, abandonment, industrial & urban development and agricultural improvement
- The species diversity of calcareous grassland in Northern Ireland is high (Cooper & McCann, 1994) & the number of nitrogen indicator species which indicate degradation of the species-rich grassland is low (NIEA, 2005). Therefore NI’s calcareous grassland appears to be of high quality.
- Giant’s Causeway & Dunseverick