LOWLAND DRY ACID GRASSLAND (UK BAP PRIORITY HABITAT)

Summary

These are grasslands and grassy stands with bracken on well-drained acid soils in the lowlands. They consist mostly of short, grazed swards of grasses growing with small herbs and mosses. Some examples contain abundant bracken growing amongst grassy swards.

These grasslands tend not to be very remarkable botanically though they can be rich in fungi, but are also of conservation value in forming part of the relatively small extent of semi- natural habitat within large areas of intensively managed farmland. They occur commonly in mosaics with neutral and basic grasslands (including agriculturally improved grasslands), scrub and rock outcrops. They are an important food source for grazing mammals, invertebrates and birds.

The vegetation of this priority habitat is developed from and maintained by grazing, which keeps the sward short and prevents larger, more vigorous from dominating at the expense of small, low-grown ones.

What is it?

These are grasslands and grassy stands with bracken on well-drained acid soils in the enclosed agricultural lowlands. They consist of swards (mostly short and grazed) of grasses such as sheep’s fescue ovina, red fescue F. rubra, common bent Agrostis capillaris, sweet vernal grass Anthoxanthum odoratum, wavy hair-grass and early hair-grass Aira praecox. The Scottish examples belong to one of four types.

Firstly there are short, patchy mixtures of F. ovina, A. capillaris and Aira praecox dotted with small plants of sheep’s sorrel Rumex acetosella, parsley-piert Aphanes arvensis and mosses such as Brachythecium albicans and Polytrichum piliferum. These belong to NVC type U1 and occur on thin, dry soils especially on the upper sun-exposed parts of rocky knolls and low hills.

Secondly there are swards of F. ovina, F. rubra, A. capillaris, A. odoratum and herbs such as heath bedstraw Galium saxatile and tormentil Potentilla erecta. These are U4 grasslands which occur on slightly deeper soils than those with U1 and in the lowlands are most common on north-western to east-facing slopes.

Thirdly there are -poor swards of D. flexuosa (U2) which occur on thin to moderately deep, well-drained soils, especially where there has been some disturbance such as burning.

Finally there are stands of bracken Pteridium aquilinum (U21a) beneath which are grassy asemblages of Festuca spp, A. capillaris, A. odoratum, G. saxatile and P. erecta similar to that in the U4 grasslands. Other forms of U20 differ in having a more heathy associated flora (U20b) or little other than bracken fronds and mats of dead bracken litter (U20c): these do not belong in this priority habitat.

Lowland dry acid grasslandis produced and maintained by grazing, which keeps the sward short and prevents larger, more vigorous plants from dominating at the expense of small, low-grown ones. This habitat can support a rich fungal flora including species such as waxcaps Hygrocybe spp. and earthtongues (Geoglossaceae).

Lowland dry acid grassland is an important food source for grazing mammals, invertebrates and birds. This priority habitat also includes lowland examples of bracken stands with a grassy underlayer.

In terms of their flora the Scottish examples are similar to most of those in England and Wales, except that the southern grass Agrostis curtisii is dominant in some examples (NVC U3) in SW England and S Wales.

How do I recognise it?

Differentiation from other Priority Habitats

This is quite a clearly defined habitat. The NVC community U1 is unique to this priority habitat. U2, U4 and U20a occur also in the uplands, so for these NVC types the defining criterion is their location within the agricultural lowlands. U3 and inland examples of SD10- 12 do not occur in Scotland. Lowland dry acid grassland can occur in close association with Lowland calcareous grassland, but the two habitats have no overlap in NVC terms. Wild thyme Thymus polytrichus is very common in Lowland calcareous grassland but comparatively rare in acid grasslands (where Rumex acetosella and Galium saxatile are more common). Among extensive bracken patches around upland fringes the priority habitat can be less clear for two reasons: (1) the U20a sub-community can be in mosaics with other (non-priority habitat) sub-communities which look the same until inspected closely, and (2) within large areas of bracken on upland fringes it might be difficult to determine whether some areas are best classed as being in unenclosed upland or enclosed lowland.

Definition in relation to other habitat classifications

Classification Habitat types belonging to this UK BAP priority habitat

NVC U1 (all examples), U2, U4 and U20a (all examples in agricultural lowlands). In England this priority habitat also includes inland examples of SD10b, SD11b and SD12. (U1 is included in the Scottish Biodiversity List.) B1 (lowland examples), C1 (examples belonging to the U20a Phase 1 sub-community in agricultural lowlands), D5, D6 (lowland examples) and H6 (examples with U1, U2, U3, U4 or U20a vegetation). UK BAP broad All examples of this priority habitat belong to the broad habitat - habitat Acid grassland.

Definition in relation to legislative classifications

Classification Habitat types belonging to this UK BAP priority habitat Habitats The Lowland dry acid grassland priority habitat does not include Directive Annex I any Annex I habitats. SNH SSSI Lowland acid grassland SSSI feature type: all examples. habitat features

Where is it?

Lowland dry acid grassland occurs on thin, well-drained acid soils in the enclosed agricultural lowlands. These sites vary from areas of level ground to steep slopes. The steeper examples tend to be broken up by rock outcrops and are particularly common on south-facing slopes. At some sites this priority habitat occupies large areas of steep, rocky slope, grading into other grassland communities (especially neutral grasslands) on deeper soils on more gentle terrain further downslope. At some other sites on more base-rich rocks and soils, Lowland dry acid grassland occupies the upper parts of slopes (in some cases just a narrow zone along the very top of the slope), giving way lower down to Lowland calcareous grassland which in turn pass into neutral grasslands on deeper soils where the slope gradient slackens. Patches of scrub, especially gorse scrub, are common among these grassland mosaics.

These grasslands are scattered through the margins between lowland and upland areas within Scotland and in the UK as a whole, on a wide range of rock types. The total extent of this habitat in Scotland has been estimated to be at least 1439 hectares (Ellis and Munro 2004), and possibly up to about 5000 hectares (Usher et al. 2000). The figure of 1439 hectares included enclosed and unenclosed U1, U2 and U4 grasslands below 300 m and was thought to be an underestimate because of under-recording of grasslands fitting this description. Such grasslands may have been under-recorded in grassland surveys, but large areas will have been recorded in more general vegetation surveys and many of these will be of unenclosed U4 grassland in areas with a cool, wet climate such as the western Highlands, where, despite being below 300 m in altitude they can be of an upland nature and should probably be excluded from this priority habitat. Grasslands similar to U1 and U4 occur in mainland Europe as far eastwards as Poland, but equivalents of U2 and U20a are unknown on the European mainland.

What is special about it?

Lowland dry acid grassland, both in Scotland and the UK as a whole, tends not to be very remarkable botanically speaking but is of conservation value in forming part of the relatively small extent of semi-natural habitat within large areas of intensively managed farmland. Some examples are important for their fungal flora e.g. ‘waxcap grasslands’. Some species of special conservation status recorded in this priority habitat are listed below.

Wildlife EC Scottish and UK BAP Habitats Bio- Red Country- Common priority Directive diversity Data side Act Group name Latin name list Annex II List List (1981) birds skylark Alauda arvensis y y y y birds linnet Cardeulis cannabina y y butterflies Coenonympha y y pamphilus bees tormentil Andrena tarsata y y mining bee fungus date-coloured Hygrocybe spadicea y y waxcap mammals brown hare Lepus europaeus y y reptiles slow-worm Anguis fragilis y y y reptiles common lizard Zootoca vivipara y y y

How do we manage it?

As with Lowland calcareous grassland, almost all examples of Lowland dry acid grassland are produced and maintained by grazing, especially by sheep, cattle and horses. At some sites this habitat is maintained largely by rabbit-grazing. Grazing prevents larger plants from taking over. In the absence of grazing coarse grasses such as false oat-grass Arrhenatherum elatius, cock’s-foot Dactylis glomerata, Yorkshire fog Holcus lanatus and Festuca rubra can thicken up within about a decade to form coarse neutral grassland of NVC type MG1, followed by colonisation by shrubs such as gorse Ulex europaeus , elder Sambucus nigra and hawthorn Crataegus monogyna (forming scrub of NVC types W21 or W23), and eventually trees such as oak Quercus spp., birch Betula spp. and sycamore Acer pseudoplatanus (W10 or W16 woodland). However, in some ungrazed or minimally grazed places with coarse grassland and scrub, Lowland dry acid grassland survives on very steep rocky slopes where the rockiness keeps the soils thin and the vegetation open so that larger plants do not out-compete small plants such as Rumex acetosella and Aphanes arvensis. In general, however, at least moderate levels of grazing are essential for Lowland dry acid grassland to be maintained.

Where Lowland dry acid grassland includes the U2 Deschampsia flexuosa grassland, this vegetation type may be a temporary feature following disturbance such as burning or scrub removal. Most U2 vegetation in Britain (in both lowlands and uplands) represents a temporary dominance of D. flexuosa on recently burned heaths or bogs, and on disturbed acid soils in felled conifer plantations. However, some patches of U2 grassland can last longer, as seen for example on some of the hills in the city of Edinburgh.

Where gorse is spreading into areas of Lowland dry acid grassland, manual cutting of this species seems to be the best method of control; burning is quicker but gorse can regenerate quickly after burning.

Good management includes avoidance of the application of artificial fertilizers which can encourage the growth of species such as perennial rye-grass Lolium perenne and white clover Trifolium repens and lead to a reduction in botanical diversity.

Good management also includes avoidance of afforestation (which leads to overshading, smothering by leaf litter and eventual loss of the grassland habitat) and quarrying (which causes a more immediate loss of the habitat).

References, links and further reading Ellis, N.E. and Munro, K. 2004. A preliminary review of the distribution and extent of BAP priority habitats across Scotland. Scottish Natural Heritage Commissioned Report No.044 (ROAME No. F00NA02). https://www.nature.scot/information-library-data-and-research/information-library

Rodwell, J.S., Dring, J.C., Averis, A.B.G., Proctor, M.C.F., Malloch, A.J.C., Schaminee, J.H.J. & Dargie, T.C.D. 1998. Review of coverage of the National Vegetation Classification. Joint Nature Conservation Committee contract report F76-01-170. Coordinated by the Unit of Vegetation Science, Lancaster University.

Rodwell, J.S. (Ed.) (1992). British Communities. Volume 3 - Grasslands and montane communities. Cambridge, Cambridge University Press.

UK BAP 2008. http://jncc.defra.gov.uk/pdf/UKBAP_BAPHabitats-26- LowlandDryAcidGrass.pdf

Usher, M.B., Bain, C. and Kerr, A. eds. 2000. Action for Scotland's Biodiversity. Scottish Biodiversity Group. Edinburgh, The Scottish Executive and The Stationery Office

MacKintosh, J. 2004. Distribution and Extent of Unimproved Lowland Grassland National Vegetation Classification (NVC) Types in Scotland. Botanical Journal of Scotland. 56(2), 119-146.

MacKintosh, J., Hawker, D., Munro, K. & Smith, M. 2004. The distribution and extent of lowland grassland National Vegetation Classification (NVC) types and Biodiversity Action Plan (BAP) habitats in Scotland. Scottish Natural Heritage Commissioned Report No. 009 (ROAME No. F97AA100).

Common Standards Monitoring guidance http://www.jncc.gov.uk/page-2199

Countryside Survey: http://www.countrysidesurvey.org.uk

National Biodiversity Network (NBN) Gateway https://data.nbn.org.uk/

Scottish Natural Heritage website: http://www.nature.scot

UK BAP information on JNCC website: http://jncc.defra.gov.uk/default.aspx?page=5155