The advantages and disadvantages of trees in the hedgerow are discussed here, with notes on the profits from hedgerow timber here.
Assuming that you want hedgerow trees, it is very much easier to plant them at the same time as planting the hedge, rather than to plant them at a later stage. It is difficult to plant into an established hedge, because it requires cutting away a section of hedge, and removing all roots from the soil in order to give space and root run for the young tree. Planting beside a hedge is easier, but the tree will be in the way of trimming operations, as well as having the other disadvantages of hedgerow trees.
There are two basic options for establishing hedgerow trees. The simplest method is to leave the leading shoots unpruned on selected plants in the new hedge, and allow them to grow up into trees, while trimming the rest to form the hedge. This can be done with either mixed or single species hedges. For example, unpruned individuals in a hawthorn hedge will form small, round-headed trees. In a beech or hornbeam hedge, selected plants can be left to grow on to form tall, branching specimens. Pruning away the lower side shoots in the early years will encourage upward growth. In later years, the rest of the hedge can be allowed to grow up for laying as required.
A second approach is to plant particular species for hedgerow trees. As well as for their site suitability, these might be chosen for their appearance, wildlife value or timber value.
The classic hedgerow tree was the elm, which largely died out in the 1970s due to Dutch Elm Disease. Elm was so prevalent because of its suckering habit. It was a spectacular, statuesque hedgerow tree, which created a unique hedgerow landscape, but was generally not popular with farmers.
Most of the native broadleaved species of tree are suitable for planting in hedgerows, including oak, ash, field maple, wild cherry, hornbeam and holly. Black poplar and willow are suitable for damp ground. Suckering trees such as aspen and the introduced poplars are not recommended, as they can cause problems in adjacent ground. Beech, small-leaved lime, and the introduced sycamore and horse chestnut cast too dense a shade for many sites, although the ability of beech and sycamore to thrive in exposed sites may be useful. Birch and mountain ash are typical of acid and upland soils, and are not normally associated with the lowland hedgerow landscape.
