Assessing the biodiversity management practices of your linear habitats

Biodiversity management practices undertaken by farmers are a key element of farm sustainability. There is a need to include biodiversity management in the assessment of farm sustainability.

This article draws on existing evidence and literature to inform the development of an innovative, affordable, repeatable and rapid assessment tool that measures biodiversity management practice on farms and gives clear messages on best practice biodiversity management. The tool combines four elements of intensively managed livestock farms, which are of high relevance to biodiversity management, namely: hedges; farm landscape structure; field margins; and watercourses.

Hedges

Hedgerow structure is important for biodiversity. There are two distinct hedge types in Ireland. Both types are good, but each requires very different management. A lack of understanding of each hedge type leads to inappropriate management and damage to hedges. Ideally, each farm should have both types of hedges present to maximise biodiversity benefits.

• Escaped (never-topped) hedge or treeline: Do not top. Side trim only;
• Topped hedges: Top to maintain as a hedge – a little above the previous year’s cut. Aim to grow up to at least 1.5m and retain a new thorn tree in every hedge.

Figure 2: Do not top an ‘escaped hedge’ and do not let a ‘topped hedge’ escape

The bigger and bulkier a hedge is the better. A hedge height over 1.5m provides suitable nest sites for birds, with adequate cover above and below their nests. Birds do not nest at the base of hedges where foxes can reach them. Neither do they nest at the top of a hedge, exposed to birds such as magpies or birds of prey.

Flowering hedges provide flowers for bees and fruit and seeds for birds and small mammals. Escaped hedges flower freely with the biodiversity value in their canopy. Topped hedges, with a dense base, provide great cover at ground level for mammals as well as nest sites.

With the recommended regular hedge cutting necessary for maintenance (little and often is recommended), there are few flowers or food on the body of topped hedges. Retaining occasional thorn trees provide flowers and food. Existing topped hedges with no mature thorn trees can be greatly improved by selecting individual or clumps of thorns from within the hedge and allow to develop into mature trees. The practice of retaining an occasional new thorn tree every year provides a diversity of tree heights. Songbirds use smaller developing trees, which are a metre or so above the body of a hedge, as ‘songposts’.

Farmed landscape structure

Agricultural landscapes can be viewed as a mosaic of habitats, many linear in nature, within agricultural land. Average field size has the strongest overall effect on biodiversity on intensively-managed farmland. The positive effect of decreasing average field size is not due to an increase in cover of natural and semi-natural areas in landscapes with smaller fields. Rather, for a given amount of natural or semi-natural cover, farmlands with smaller fields have higher biodiversity.

Linear habitats are networks or corridors for nature through the countryside. Their greater edge:area increases habitat diversity. Under the Environment Impact Assessment (Agriculture) Regulations, permission must be sought from the Department of Agriculture, Food and the Marine where hedge removal will result in a field over 5ha. Farmed landscape, with average field size less than 5ha, provides networks for nature and corridors of movement for birds, bats, bees and butterflies to move through the countryside.

Field margins

Field margins are a rough grass habitat, which is absent from a lot of intensively-managed farmland in Ireland. Uncultivated and unsprayed field margins allows the rough grass margin to continue undisturbed, protecting the soil biodiversity. Their presence allows grasses and wildflowers to flower and seed, providing habitat for associated invertebrates, birds and small mammals. Birds such as linnet feed on grass seed.

There is a high biodiversity value in native plants growing wild naturally. Wildflowers growing wild in unimproved field margins - undisturbed and unfertilised for millennia - are not to be confused or equated with sowing unregulated packets of flower seed following cultivation and the pre-existing plants (or ‘weeds’) sprayed-off to make the area look ‘pretty’ for a short time until the process is repeated. In this latter case, the word wildflowers has been hijacked. We need to maintain our native species of flora and fauna, which have been here for thousands of years and are in tune with each other with regards timing of flowering and other growth stages. Some are inconspicuous – in other words, they may not be ‘showy’ or attractive to humans.

Actions to protect our declining biodiversity must be evidence-based and directed by science, rather than individual preferences. It cannot be about actions that make the landscape attractive to humans, those that are easiest, or about focusing on one species at the expense of others.

Watercourses

All watercourses are important for biodiversity, including small watercourses and drains which are important in their own right, and also important for their influence on larger watercourses. Fenced watercourse banks prevent siltation from eroded banks and allow natural bankside vegetation to flourish.

Watercourse margins provide further protection for watercourses and allows space for native wildflowers and grasses to grow, providing habitat for associated fauna. Prevention of livestock drinking access to watercourses prevents siltation of watercourses and protects the habitat for instream biodiversity.

Valuable habitats

Linear habitats comprising hedges, field margins and watercourses are valuable habitats for biodiversity within the farming platform, alongside land managed for agricultural production. Best practice biodiversity management practices on these linear habitats are important. Complete the Teagasc Biodiversity Management Practices Self-Assessment Tool: Linear Habitats for your farm here.

This article by Catherine Keena, Teagasc, and Jim Kinsella, University College Dublin, first appeared in the Beef 2022 'Supporting Sustainable Beef Farming' open day book.

National Biodiversity Week Ireland 2023 takes place 19^th–28^th May. 'Explore the rich variety of life in Ireland this May with a host of wonderful events and activities for the whole family.' Find out more about National Biodiversity Week here.