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Farmland Biodiversity

| Field Margins | Farmland Biodiversity/Natural Heritage | Birds of Conservation Concern |

Native Irish Hedgerows

Species

The more species of trees, shrubs and ground flora in a hedgerow, the more wildlife it will contain. Some trees or shrubs support a wide variety of wildlife. Hawthorn supports over 200 insect species. Of the hedgerow trees, willow and oak are particularly valuable, each capable of supporting over 400 different insect and mite species, while the field maple, sycamore and horse chestnut support less than 50 species.

Some trees or shrubs supporting less variety of wildlife may be valuable as the main or only food source of a particular species. For example, the brimestone butterfly depends primarily on the occurrence of buckthorn.

A varied composition provides continuity of food supply for birds and small mammals, with seeds, fruits and berries ripening at different times.

Structure

The detailed structure of a hedgerow determines its use as nest sites, song posts, feeding sites, cover from predators, roosting sites or corridors for movement.

Birds such as dunnocks, robins and wrens prefer a hedgerow which is thick at the bottom, which provides cover when scratching for insects particularly in winter when the open ground may be frozen. The bottom of the hedgerow with its carpet of dead leaves will remain unfrozen and thus provide a rich source of food.

Tall shrubs provide the higher vantage points and nest sites preferred by birds such as wood pigeon. Small trees and saplings only a metre or so above the body of the hedgerow are used regularly as song posts by the blackbird and songthrush amongst others.

Laid hedgerows offer more nest sites for birds and concealed hibernating places for invertebrates

Ideally hedgerows should be thick at the base and are made up of tall trees and and shrubs.

Size

The larger the hedgerow volume, the better it is for birds. It must be at least 4'6" (1.4m) tall and 4' (1.2m) wide for birds to breed successfully. Most songbirds that nest in a hedgerow prefer to site their nests at least 4' (1.2m) from the ground to avoid ground predators. They also need overhead cover to avoid detection by magpies. Obviously the bulkier a hedgerow, the more food and concealment it provides.

Management of Hedgerows

Hedgerow Type Management
Hedgerows with a dense base Side trim sides to a triangular shape from a wide base leaving the peak as high as possible. Leave trees and shrubs (including thorns) at irregular intervals.
Relict Hedgerow (line of mature trees with full canopy and distinct bole) Leave alone. Overhanging branches may be side trimmed. Fencing off would allow a strip of natural grassland, scrubland to develop and possible natural regeneration.
Escaped Hedgerow (a hedgerow which has grown up into a line of leggy shrubs, but not yet mature top-heavy trees) Rejuvenate by laying or coppicing. Fencing off would allow natural regeneration. Do not top.