Glasgow & SW Scotland Butterflies

Glasgow & SW Scotland Branch Website

March 7, 2009

Definitions of Grassland Habitats for Conservation Management

Grassland Habitat categories using Phase 1 Habitat Survey Descriptions

When reading descriptions of species habitat preferences and reviews of conservation techniques, I’ve often wondered how ‘experts’ tell different types of grasslands apart. This can be important in defining the specific habitat conditions required for the conservation of our endangered native butterfly and moth species.

The following definitions are taken from the Handbook for Phase 1 habitat survey methods published by the Joint Nature Conservation Committee. A phase 1 habitat survey is a technique used by environmental consultants and others interested in auditing environmental characteristics of a location to assess conservation values. For images of some of the species mentioned see http://www.floralimages.co.uk/.

Most grasslands have been subjected to some degree of agricultural improvement by repeated grazing, mowing, fertilising, drainage or herbicide treatment.  It is important to try to distinguish unimproved and semi-improved from improved grasslands. However, these types of grassland often for a continuum so that it is not normally possible to define each with precision, especially as species critical for definition are often only observable for a short season of the year.

Agricultural improvement usually results in a decrease in floral species diversity of the sward and dominance of a few quick-growing grasses such as Perennial Ryegrass (Lolium perenn), Yorkshire Fog (Holcus lanatus ) and Red Fescue (Festuca rubra). The resulting sward composition is likely to vary  with intensity of treatment, so careful observation and field work is often required to define and maintain boundaries between these categories.

Calcareous Grassland Thyme and Rock-Rose

Calcareous Grassland Thyme and Rock-Rose

Unimproved Grassland

Unimproved grasslands are likely to be rare in lowlands. They may be rank, neglected, mown or  grazed. They may have been treated with low levels or farmyard manure in the past, but should not have had sufficient applications of fertiliser or herbicide, or have been intensively grazed or drained so as to alter the sward composition significantly. Species diversity is often high with species characteristic of the area and soil type with a low percentage of agricultural species.

Semi-improved Grassland

Semi-improved grassland is a transition category made up of grasslands which have been modified by artificial fertilisers, slurry, intensive grazing, herbicides or drainage and consequently have a range of species which is less diverse and natural than unimproved grasslands. Such grasslands are still of some conservation value. Semi-improved grasslands may originate from partical improvement of acid, neutral or calcareous grassland. Often the improvement of the site can reduce the distinctive characteristics of acid or calcareous grassland, so that this is not always easy to distinguish in the field. Species diversity will generally be lower than in unimproved grassland in the same area. If key signs of improvement are missing (see below), then the grassland is likely to be semi-improved.

Improved Grassland

Improved grasslands are those meadows and pastures which have been so affected by heavy grazing, drainage or the application of herbicides, inorganic fertilisers, slurry or high doses of manure that they have lost many of the species which one could expect to find in an unimproved sward. They have only a very limited range of grasses and a few common herbaceous flowering plants, mainly those demanding of nutrients ands resistance to grazing. Perennial Ryegrass (Lolium perenne), Crested Dogstail (Cynosurus cristatus),  White Clover (Trifolium repens), Common Sorrel (Rumex acetosa) Dandelion (Taraxacum officinale) Daisy(Bellis perennis) Meadow Buttercup (Ranunculus acris) and  Bulbus Buttercup (Ranunculus bulbosus) are all typical of improved grassland, while stands of dock (Rumex species), common nettle (Urtica dioica) and thistles (Cirsium Species) indicate local enrichment of the soil by grazing animals.

The following signs usually indicate substantial improvement:-

i) Bright Green, Lush and even sward, dominated by grasses

ii) Low diversity of herbaceous flowering plants

iii) More than 50% Perennial Ryegrass (Lolium perenne), White clover  (Trifolium repens)  and other agricultural species.

Fields which have been reseeded in the past and have since become somewhat more diverse are included in this category, but recently seeded monoculture grassland such as ryegrass leys and fields of arable crop species are classified as Cultivated Land.

Small Pearl-Bordered Fritillary on Ragged Robin

Small Pearl-Bordered Fritillary on Ragged Robin

Acid Grassland

Grassland in this category is often unenclosed. As on hill grazing land and occurs on a range of acid soils (pH less than 5.5). It is generally species poor and often grades into wet or dry dwarf shrub heath, although it will have less than 25 % dwarf shrub cover (see Heath definition below). Pioneer annual-rich calcifuge (alkaline-intolerant) communities on dry sandy soil are included in this category, as are wet acidic grasslands typified by species such as Heath Rush (Juncus squarrosus). The following species are indicative of acidic conditions when frequent or abundant:Wavy Hair-Grass (Deschampsia flexuosa), Mat Grass (Nardus stricta), Heath Rush (Juncus squarrisus), Heath Bedstraw (Galium saxatile) and Sheep’s Sorrel (Rumex acetosella).

Neutral Grassland

Typically enclosed and usually more intensively managed than acid or calcareous grassland (except on roadside verges), this category encompasses a wide range of communities occurring on neutral soil (pH 5.5-7.0). The following are indicative of neutral conditions when frequent or abundant: Meadow Foxtail (Alopecurus pratensis), False Oat-grass (Arrhenatherum elatius), Crested Dogstail (Cynosurus cristatus), Cock’s Foot (Dactylis glomerata), Tufted Hair-grass (Deschampsia cespitosa), Tall Fescue (Festuca arundinacea) and Meadow Fescue (Festuca pratensis).  Perennial Ryegrass (Lolium perenne) may be present, but when abundant it is indicative of improved grassland.

Hay meadows will usually fall within this category. After cutting a hay meadow can have the appearance of improved grassland as the new growth comes through. Included in neutral grassland is a range of grasslands which are inundated periodically, permanently moist, or even water-logged. Some examples include: Water meadows, alluvial meadows and Wet pastures where grasses are dominant but with species such as Marsh Marigold (Caltha palustris), Meadow sweet (Filipendula ulmaria), Valerians (Valeriana species), Rushes (Juncus species) or Marsh Hawksbeard (Crepis paludosa ) present.

Calcareous grassland

These grasslands are often unenclosed, not managed intensively and occur on calcareous soils (pH above 7.0). Mountain avens (Dryas octopetala) communities are included. Where grass is tall the dominant species is usually either Drooping Tor-grass (Brachypodium pinnatum) or Upright Brome (Bromus erectus), whilst species indicative of short, close-grazed and species-rich calcareous turf are Crested Hair-grass (Koeleria macrantha), Downy Oat-grass (Avenula pratensis), Blue Moor-grass (Sesleria albicans), Common Rock-Rose (Helianthemum nummularium), Salad Burnet (Sanguisorba minor), and Wild Thyme(Thymus polytrichus).

Other definitions

Heathland is classified as being dominated (greater than 25 %) by heathers or dwarf gorse species. 

Scott Shanks

 

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