Calcareous Grasslands Habitats – What are they?
Calcareous grasslands are highly diverse habitats forming where soil fertility and acidity is low, and where moderate grazing and browsing by livestock helps to balance the competition between plant species.
They are threatened by the intensification of agriculture and the abandonment of traditional grazing regimes – hope for these habitats lies in the removal of excess nutrients from the soil and modifying the ecology of the grassland system.
Calcareous grasslands are grassland habitats that are characterised by high alkalinity, forming on free-draining mineral soils. In general, they are associated with low-intensity agriculture, and as a result, are formed on soils that are relatively low in nutrients. Grazing/browsing activity is important in their formation, however, influences the types of grasses which populate the habitat. Similar habitats which are not grazed/browsed tend to form meadows with a different cohort of grass species.
(NOTE: Grazing and browsing are not the same thing – grazing is the eating of “soft”, herbaceous vegetation by animals, while browsing is the eating of “hard”, woody vegetation. In this article, when we refer to “grazing”, we mean both grazing and browsing.)
Calcareous Grassland Habitats in Ireland
In Ireland, calcareous grasslands habitats are restricted in their distribution, and can be found mainly along the slopes of eskers and moraines (geological features produced during the last Ice Age by the glaciers which covered Ireland) in the midlands, and elsewhere on shallow rocky limestone soils. Certain calcareous grasslands (those with a high diversity or abundance of orchid species, or with juniper growing) fall under Annex 1 of the EU Habitats directive – these are protected sites and must be shielded from the negative impacts of developments that could affect them.
Biodiversity of Calcareous Grasslands
The biodiversity of calcareous grasslands is high compared to more acidic and nutrient-rich grasslands. Acidic soil conditions are not ideal for many plant species, and (perhaps surprisingly) neither is high soil fertility! When soil fertility is high, a small number of vigorously growing species (especially certain grasses) can “take over” the area, excluding other slower-growing species. When soil fertility is low, the playing field (if you’ll forgive the pun) is levelled – fast-growing species cannot get enough nutrients to grow as aggressively, while slower-growing species get a chance to establish themselves. Species richness (the number of species in an area) can be high in calcareous grasslands, up to 45 species per square metre! In highly calcareous soils, orchid species are supported – orchids are relatively delicate plants, often requiring particular soil conditions to grow and spread in. Their seeds rely heavily on symbiotic fungi in the soil to begin growing, and if soil conditions are not correct for the correct species of fungi, the orchids will not grow.
Impact of Livestock on Calcareous grasslands
An important aspect of calcareous grasslands related to their high biodiversity is the fact that they are grazed/browsed by livestock. While high-intensity grazing can destroy the species richness of an area, light grazing can actually help to increase it. Livestock can be “picky” about what plants they graze on, and leave other plants behind. This helps to further eliminate the competitive advantages certain otherwise dominant species might have. In addition, livestock can help to increase the diversity of micro-habitats in the grassland through stripping certain areas bare and disturbing the soil. Their dung and dead bodies (if not removed) also provide “hotspots” of nutrients for not just plants, but also for invertebrates and other eaters of decaying organic material.
Calcareous grasslands, along with other semi-natural grassland types, are under threat from the intensification of agriculture in some places, and the total abandonment of it in others. Intensive agriculture adds a huge amount of fertiliser to soils, which highly favours the growth of a select few competitive species. As mentioned, high levels of grazing by livestock in intensive farms can lead to a similar situation. On the other hand, when land is abandoned and not managed at all by humans or their livestock, grasslands can begin to be invaded by tough scrub vegetation, which excludes the rich diversity of plants that would otherwise be able to grow.
Restoration of Calcareous Grassland habitats
Restoration of damaged calcareous grasslands can be done in a few ways. Fertiliser addition to the soil must be stopped, and further removal of nutrients from the system can be achieved by cutting grass and removing the hay or through reinstatement of a grazing regime. Management for calcareous grasslands must be carefully considered. Livestock can have harmful effects on the ecosystem – trampling can limit the survival of earthworms and slugs, and grazing activity can reduce the camouflage properties of vegetation, which has important implications for the survival of bird species which need to hide from predators. If cutting is not timed correctly, ground-nesting birds such as corncrake can have their nests destroyed and their chicks killed. Deturfing is a drastic option – this involves removing layers of topsoil entirely. While this can be very effective and also create habitat for colonisation by new species, it is highly destructive and labour-intensive and so isn’t the best option for every restoration project. A more subtle approach to calcareous grassland habitat management is the introduction of hemiparasitic plants like yellow rattle. This species is the plant equivalent of a vampire – it sucks nutrients and water from the roots of competitive grass species, weakening them and giving other plants a chance to grow.
Written by Tom Murphy
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