Information and Advisory Note Number 11 Back to menu

The management of unimproved lowland grassland for nature conservation

1. Introduction: the necessity for management

1.1 Our main aim in conserving unimproved grasslands is to maintain or, if possible, enhance their biodiversity. To do this we must mimic the conditions that have maintained them over the centuries. The farming systems that have produced semi-natural grasslands in Britain have done so by maintaining a stable (or sometimes decreasing) level of nutrients and a stable standing crop from year to year, while removing the annual net primary production. In other words, some sort of management that harvests the year's growth is essential.

1.2 It is usually wise to work on the principle that the best management regime for a site is that which has led to its current level of interest. This may not be the management of recent years, but the traditional regime that was followed before any intensification took place.

1.3 Truly natural grasslands, which do not change into scrub or woodland in the absence of management, are confined to places such as cliff tops and mountains, where a harsh environment prevents tree or shrub growth.

2. Types of grassland

2.1 Grasslands can be broadly classified according to the base status of their underlying substrate, as in Rodwell (1992). Calcicolous (or calcareous) grasslands, on base-rich soils, are usually species-rich; meso-trophic (or neutral) grasslands, on neutral soils, are less so; and calcifuge (or acid) grasslands, on base-poor soils, are comparatively species-poor. It is not invariably so in other countries. One theory to explain this pattern of species-richness in Britain is that acidic substrates have been rare during recent evolutionary time so that relatively few species have adapted to acid habitats.

2.2 Base status is not the same as nutrient status, so base-rich soils are not necessarily fertile soils. Highly fertile soils are also a relatively recent phenomenon, and have also been colonised by a small number of species. So highly fertile soils normally support species-poor grassland while species-rich grassland is almost always found on soils of low fertility.

2.3 Improved grassland can usually be recognised by the presence of large amounts of one or more of the following species:
Lolium perenne (Perennial Rye-grass)
Trifolium repens (White clover)
Dactylis glomerata (Cocksfoot)
Holcus lanatus (Yorkshire-fog;
Phleum pratense (Timothy).

3. Management options

3.1 Grazing, if not too heavy, produces structural mosaics in the vegetation associated with the palatability of individual species. Trampling, dunging and defoliation all contribute to the small scale pattern of variation. Plants and animals benefit from the variety of structural features present in lightly or moderately grazed pastures but heavy grazing eliminates structural diversity.

3.2 Cutting causes a sudden and dramatic change in habitat which invertebrates, birds and small mammals are ill-equipped to deal with. It removes the flowers and seed heads which are important to many invertebrates and leads to a lack of bare soil and of structural variety in the sward, so the invertebrate population of cut grassland is generally poorer than that of pasture. However, grassland cut for hay or silage is almost always grazed after being cut, and grass cutting is, of course, an essential part of livestock management, providing winter feed.

3.3 Burning is rarely used in the management of lowland grassland in Scotland. It is a catastrophic event from which invertebrates may not easily recover. Some are killed while others lose their food sources and overwintering sites. Fire can also be devastating to ground-nesting birds, and although some mammals may be protected by living in burrows, they too are affected by the loss of food sources.

4. Grazing

4.1 Conservationists sometimes assume that the priority when setting a grazing regime for grasslands is to avoid summer grazing in order to allow plants to flower and set seed. However, research suggests that the seedling establishment phase is the most critical period for most if not all plants so it is important to set a level of grazing that keeps the sward open and free of excess litter, and creates gaps in which seedlings can establish. Many invertebrates also require patches of bare soil.

4.2 Different plant species germinate at different times, so gaps for regeneration are needed throughout the year. This means that continuous light grazing throughout the year is a perfectly acceptable management regime.
If grazing is to be excluded for a period it should be for a good reason, such as:

to get a good show of flowers, for the benefit of invertebrates and/or for the public
to avoid poaching during the winter, especially on poorly drained sites.

4.3 Optimum stocking levels are notoriously difficult to determine and any decision should be based on the current condition of the sward. Are there signs of damage by overgrazing such as poaching, soil erosion on slopes or a very short sward with excessive areas of bare earth and invasions of thistles, docks or ragwort? Or is undergrazing leading to a sward choked with long grass and uneaten litter, where plants cannot find space to regenerate?

4.4 Supplementary feeding of stock in winter (with the exception of mineral licks or blocks) should be avoided on unimproved grassland since it imports nutrients and foreign seed onto the site and encourages poaching around the feeding areas. The stock, meanwhile, are of little benefit to the grassland while not grazing it. If supplementary feeding is unavoidable, feeding sites should be moved regularly to minimise poaching.

4.5 Different types of stock are appropriate for different situations:

Sheep are good at selecting preferred species and avoiding unpalatable species, which can have the effect of suppressing species of nature conservation value. They find it difficult to graze long grass which has been ungrazed for a while. However, their light weight can be an advantage on steep or fragile sites.
Cattle are less able to select or avoid particular species and can eat tall, coarse vegetation. They are generally the preferred stock type for conservation management of grassland but, being heavy, can poach and damage the sward.
Goats prefer to browse or eat coarse vegetation and are useful for controlling scrub and rushes.
Horses and ponies will graze some areas very closely and others (particularly their latrine sites) not at all, so tend to produce a mosaic of over-grazed vegetation and patches of rank weedy grass.
Hardy or primitive breeds are exceptions to these general characteristics and can be useful for conservation management. For example, older or mountain breeds of sheep can eat coarser vegetation than modem or lowland breeds and Welsh Mountain ponies, which are small and light, have been used to graze coarse grassland during winter without poaching.

5. Cutting

5.1 Modem techniques allow hay and silage to be harvested much earlier but many plants of hay meadows do not set seed until well after traditional cutting dates anyway and will probably survive if an occasional very late cut allows regeneration by seed once every few years. However, late flowering perennials which regenerate primarily by seed and do not have a persistent seed bank are susceptible to
regular early cutting. Few annuals occur in meadows since there is insufficient time, even in traditionally managed hay meadows, for most annual species to flower and set seed. Meadows which are regularly cut late will give annuals and late flowering perennials the greatest chance of survival, but will produce poorer hay, so a compromise such as rotational cutting (leaving a different area uncut each year) should be considered where there is a conflict of interests.

5.2 Research in the Yorkshire Dales has shown that grazing outside the hay-growing period is essential to maintain the species-richness of hay meadows and that spring grazing and autumn grazing favour different groups of species. Both should be continued where this has been the traditional management. Grass cuttings that are left in situ are likely to smother the underlying vegetation, leading to a loss of species-richness.

5.3 Late cutting also avoids disturbance to ground nesting birds. When cutting it is important to adopt a mowing pattern that allows birds and other wildlife to escape and retains some cover at field comers and edges to provide protection from predators. This can be grazed with the aftermath (which is the growth of grass after cutting).

6. Fertilisation

6.1 The conservation value of unimproved grassland derives principally from the fact that nutrients are limited, plants are therefore under stress and growth rates are restricted. These conditions suit a large number of "stress tolerant" species. The addition of nutrients reduces this stress and allows the rapid growth of a small number of highly competitive species, so that fertile soils invariably support species-poor grassland. Over the past few decades fertilisation and reseeding have changed the composition of most of our lowland grasslands to species-poor rye-grass (Lolium perenne) - dominated communities

6.2 Modem agriculture relies heavily on the application of inorganic (or mineral) fertilisers to produce high yields and a highly palatable grass crop. Nitrogen (N), phosphorus (P) and potassium (K) are the three most commonly used nutrients and N is usually applied in the greatest quantities. These nutrients encourage the growth of competitive grasses at the
expense of most other species and so reduce species-richness and diversity in grassland. Even the very small amount of 25 kg N/year has been shown to encourage the spread of agriculturally productive grasses and reduce species-diversity. (Intensively managed grassland can receive well over 300 kg N/year.) So inorganic fertilisers should never be applied to semi-natural grasslands.

6.3 Animal slurry and farmyard manure are organic fertilisers that provide the same nutrients, N, P and K, as inorganic fertilisers and can have the same damaging effects. Slurry should never be used on semi-natural grasslands, not only because it will cause a decline in species-richness but because it may scorch the sward as well, creating highly fertile patches of bare ground which will be readily colonised by weed species. However, manure releases nutrients more slowly and over a longer period of time than slurry or inorganic fertilisers, and does not provide the same advantage to competitive species. So limited applications of farmyard manure may be acceptable where this has been part of the traditional management of a site.

6.4 Lime, like farmyard manure, has been added to some semi-natural grasslands for centuries, in order to reduce soil acidity and thus increase the availability of nutrients. It should never be added to sites with characteristic acidic communities but, where moderate liming is a long established practice, it may be continued.

Reference

Rodwell, J.S. (ed) (1992). British Plant Communities Vol 3 Grasslands and montane communities. Cambridge: Cambridge University Press

Author

Jane MacKintosh

Contacts for advice and information

Jane MacKintosh, Grassland Ecologist

Daniel Gotts, Agricultural Landscape Ecologist

Dr Helen Armstrong, Upland Grazing Ecologist

Dr David Philips, Invertebrate Ecologist

Dr Stephen Ward, Advice on management agreements

Scottish Natural Heritage
Research and Advisory Services Directorate
2 Anderson Place
Edinburgh
EH6 5NP
Tel: 0131-447 4784

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