Grassland: Selecting indicators of success for grassland enhancement (TIN050)

Indicator species

These indicators of success set targets for the number and frequency of positive plant indicator species for the target habitat or community at set times during the life of the agreement. Indicator species are listed in the FEP handbook and discussed in more detail below. The cover of negative and undesirable species should be dealt with under the agreement prescriptions.

The indicators should be set at a level that is challenging enough to encourage optimum management, but also realistic enough to be met if such management takes place. This is not easy!

As each site is unique it is not possible to be completely prescriptive in this guidance. The following are the main factors that will determine the level at which the indicators should be set.

The starting point is important. Indicators need to be informed by good site information from the FEP and/or observations. This information will:

  • allow an assessment of the botanical interest;
  • provide a measure of restoration potential; and
  • provide a base-line for future assessments.

It should be expected that any indicator species present at the start of enhancement work become more frequent during the lifetime of the agreement, while indicator species that are reintroduced should become established. Some natural re-colonisation might also occur depending on local circumstances such as proximity to species-rich grassland and viability of the seed bank (significant only in sites that recently held species-rich grassland).

Material used for enhancement is important. Species-rich green hay has proved to be a cost-effective means of restoring species-rich grassland communities. If this method is used the hay should come from a nearby site with similar conditions of soil, aspect and altitude to the receptor site and the species composition of the donor field should be known. A list of potential desirable colonists can be drawn up from this. Note, the timing of the hay cut will affect seed content and composition and therefore what establishes.

Some indicator species colonise better than others and many of the most desirable ones perform poorly and struggle to compete with grasses. These are mostly the habitat specialists associated with infertile soils, that are good at tolerating stresses such as lack of nutrients, extremes of pH or drought (for example devil's-bit scabious, great burnet and wild thyme).

Even with good preparation of the receptor site some of these species perform poorly. For example, they may have specific germination requirements which severely limit their ability to colonise new sites. Some thyme and rockrose species are associated with the nests of yellow meadow ant, perhaps because they provide hot, well-drained microsites for germination. The presence of the ant is not essential for these plants to grow, but it's presence or absence may help set targets for the indicators.

Species that perform well tend to be those that:
  • are good at colonising any gaps in the sward;
  • are good competitors;
  • capable of vegetative spread;
  • tolerant of a wide range of conditions;
  • and may be seen on relatively fertile grassland (for example oxeye daisy, common sorrel and yarrow).

Competitive ability and the capability for vegetative growth become increasingly important as the vegetation develops into a closed, established sward and young plants have to compete with well established ones.

Many of the poor performers are those that are constant characteristic species of the target (BAP habitat) plant communities. Success in establishing these more challenging species will be key in fully restoring BAP habitats. Many are also the food plants of invertebrates of conservation value. They are likely to have the best chance of success where conditions on the receptor site are suitably stressful and management is optimal - here they can sometimes do reasonably well.

Yellow-rattle is a special case. It has attributes which make it a useful tool for the diversification of productive grassland, ie:

  • it is associated with the target communities (species-rich grasslands);
  • seed is easily obtained at moderate cost (although it is easily damaged so particular care should be taken concerning suppliers, seed viability, storage and sowing times);
  • it reduces the vigour of competitive species and allows establishment and persistence of target species; and
  • it can colonise rapidly and persist in fertile grasslands.

Excessive populations of yellow-rattle (which can lead to extreme declines in yield for the farmer) can be controlled readily by commonly-used management practices such as grazing, the application of farmyard manure at sustainable levels or (in extreme cases) cutting before seed set.

With sites that are to be managed as hay meadows yellow-rattle should usually be included as an indicator.

The species listed below are divided into three broad categories relating to their ability to colonise new sites. These should be treated with caution and used only as a general guide. Note, some require particular soil types or conditions. Those listed as indicators in the FEP handbook are shown in bold. (N = neutral grassland/lowland meadow, C = lowland calcareous grassland, A = acidic grassland/heathland).

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