Tayside Biodiversity Partnership Local Action Plan

Calcareous and Base-Rich Grassland

INTRODUCTION
Calcareous grasslands are found on shallow lime-rich soils, derived from lime-rich bedrocks. Although this Habitat Action Plan primarily covers calcareous grasslands on both in-bye and hill ground, it also covers grasslands overlying
base-rich substrates. These grasslands are generally botanically diverse and can support many uncommon plants. Tayside, particularly Perthshire, contains significant areas of these types of grassland. The calcareous and base-rich
grasslands are generally managed as grazing land.

In addition, there are a number of small exposures of Limestone Pavement and Granular Limestone. Limestone pavements were exposed by the scouring of ice sheets during the last ice age. Subsequent erosion has formed a complex pattern of crevices (grikes) between massive blocks of limestone (clints). Granular limestone occurs as small friable areas of limestone associated with pavement.

DEFINITION
The UK Biodiversity Steering Group defines calcareous grassland as National Vegetation Communities CG1-14 and divides calcareous grassland into Lowland Calcareous Grassland and Upland Calcareous Grassland. Of these community types, the Lowland grasslands (CG1-9) do not occur in Scotland. As such all the calcareous grassland in Tayside is considered to be Upland Calcareous Grassland at whatever altitude it occurs.

The grasslands over-lying the base-rich rocks and soils are a poor fit into the NVC Communities CG10 and CG11, but they do have similarities in the species they support. Although less species-rich than the official CG10 and CG11, many of the more common species are found. Such calcareous grasslands found in Tayside are defined as CG10: Festuca ovina - Agrostis capillaris - Thymus praecox; CG11: Festuca ovina - Agrostis capillaris - Alchemilla alpina; CG12: Festuca ovina - Alchemilla alpina - Silene aucaulis (montane grassland); and CG14: Dryas octopetala – Silene aucaulis (cliff ledges).

This habitat comprises a diversity of grassland characterised by the prominence of calcicolous (calcium-loving) grasses and herbs. Swards tend to be more species-rich than grasslands on more acidic soils and may contain over 60 species per 4m2. The montane forms of calcareous grassland are often enriched by a distinctive assemblage of Arctic-alpine plants such as Alpine lady’s mantle Alchemilla alpina, Alpine bistort Persicaria viviparum, Moss campion Silene acaulis, Yellow saxifrage Saxifraga aizoides, Purple saxifrage Saxifraga oppositofolia and Lesser club moss Selagainella selaginoides.

KEY SITES
The main areas noted in the biodiversity audit for Tayside are:

Ben Lawers NNR, Beinn a’Ghlo SSSI, Ben Vrackie SSSI and Caenlochan NNR (Glen Doll and Glen Fee). Tulach Hill and Glenfender Meadow SSSIs are partly on Dalradian limestone and include calcareous grassland.

In addition to the SSSI’s, there are numerous areas of calcareous grassland located within the Breadalbane area of Highland Perthshire.

SWT have identified Wildlife Sites containing calcareous / base-rich grasslands:

Tigh An Eilein, Glenshee
Loch Kinardochy and Tomphubil Limekiln, Tummel Bridge
Kiltyrie Meadows, Loch Tayside
Grandtully Meadow, Strathtay
Gleann Beag, Glenshee

Edintian Bog, Glen Fincastle
Creag Mhor, Loch Tummel
Gleann Taitneach
Auchleeks
Tonguey Faulds

SWT have also designated the following Wildlife Sites for their Limestone Pavement/Granular Limestone:

Allean Forest Limestone, Loch Tummel
Trinafour

Meall Ban
Lassintulloch

CURRENT STATUS AND EXTENT OF HABITAT
Only a small proportion of the region overlies limestone, but a broader band of mica-schist and calcareous grasslands (NVC CG10 and CG11) is quite widespread in the north and west of Tayside; base-rich igneous rocks occur in the Sidlaw and Ochil hills. At present there is no figure available for the total area of calcareous and base-rich grasslands in Tayside.

Limestone Pavement

Limestone pavement is one of Britain’s most threatened habitats and is a scarce and non-renewable resource.

The total area in the UK is less than 3,000 ha. with only a small proportion occurring in Scotland. Such pavements are of both geological and biological importance. The vegetation, often containing unusual
combinations, is rich in plants, bryophytes and lichens.

It will vary according to geographical location, altitude, rock type and the presence or absence of grazing
animals.

KEY SPECIES

P = UK Priority species C = UK species of conservation concern

Birds	Black grouse	Tetrao tetrix	P
Invertebrates	a mason bee	Osmia inermis	P
	Cuckoo wasp	Chrysura hirsuta	P
	Northern brown argus	Aricia artaxerxes	P
	Small blue butterfly	Cupido minimus	C
	Mountain ringlet	Erebia epiphron	C
	a micro-moth	Ancylis tineana	C
	a leaf beetle	Cryptocephalus primarius	P
	Bumble bees	Bombus spp.
Molluscs	Round-mouth whorl snail	Vertigo genesii	P
	Geyer’s whorl snail	Vertigo geyeri	P
Plants	Purple colt’s foot	Homogyne alpina	C
	Purple oxytropis	Oxytropis haller	C
	Alpine fleabane	Erigeron borealis	C
	Common rockrose	Helianthemum nummularium
	Wild thyme	Thymus praecox
	Alpine lady’s mantle	Alchemilla alpina
	Quaking grass	Briza media
	Autumn gentian	Gentianella amarella
	Kidney vetch	Anthyllis vulneraria
	Hair sedge	Carex capillaris
Fungi	Date-coloured waxcap	Hygrocybe spadicea	P

The calcareous grasslands of the area are important for several rare plant species and Ben Lawers and Caenlochan Glen are among the top sites for alpine plants in the UK. These include Purple colt’s foot Homogyne alpina at Caenlochan NNR, Alpine fleabane Erigeron borealis on Ben Lawers and Caenlochan and Purple oxytropis Oxytropis halleri on Ben Vrackie.

In addition to these rare alpine plants, other plants associated with calcareous/ base-rich grasslands include Rock rose Helianthemum nummularium, Wild thyme Thymus praecox, Alpine lady’s mantle Alchemilla alpina, Quaking grass Briza media and Autumn gentian Gentianella amarella. Another UK priority species is the fungus Date-coloured waxcap Hygrocybe spadicea.

On the limestone pavement Hair sedge Carex capillaris (a BSBI national scarcity) and Kidney vetch Anthyllis vulneraria are found.

The flower-rich grassland supports a wide range of insects. Several of these are listed as priority species within the UK BAP - the Mason bee Osmia inermis, for instance, is found only on baserich upland grasslands and limestone pavement - including a south-facing limestone escarpment near Blair Atholl. A parasite of the mason bee, a Ruby-tailed wasp Chrysura hirsuta and the Northern brown argus butterfly Aricia artaxerxes are also found in Tayside.

COMMON ROCKROSE

Wild thyme grows, often in mats, in short limestone turf
or even directly on the rock on dry south-facing slopes.
Seen here with the low-growing Eyebright Euphrasia
spp., Wild Thyme is much appreciated by butterflies and
bumblebees. In the Highlands thyme tea used to be
popular as an everyday beverage.

The Northern brown argus is a UK BAP Priority Species. Found in scattered colonies across Scotland and Northern England strong populations have been recorded in Highland Perthshire and the Sidlaw Hills where the sulphur-yellow Common rockrose grows. Although the butterfly uses other plants such as Common Storksbill Erodium cicutarium and Knapweed Centaurea spp. it is dependent upon Common Rockrose as it is the main foodplant for its caterpillars. Single eggs are laid on the upperside of the plant’s leaves.

The butterfly’s overall decline is due not just to the loss and fragmentation of habitats but also to a change in grassland management practices. It benefits from its habitat undergoing light grazing either by livestock or rabbits to ensure open sward conditions. The species has, however, been recorded as absent from many heavily grazed sites even when there is an abundance of its foodplant.

NORTHERN BROWN ARGUS

Other species associated with calcareous grasslands include the Small blue butterfly Cupido minimus in coastal areas and the Mountain ringlet Erebia epiphron on upland mica schist. Various Vertigo species of snail are found on calcareous habitats: two UK BAP species are known in Tayside - the Round mouth whorl snail Vertigo genesii and Geyer’s whorl snail Vertigo geyeri.

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