Non-woodland planting

This includes avenues, orchards, arboreta or individual trees in parks, gardens and streets. Arboreta and orchards by their nature comprise non-native species, and non- natives may also be the appropriate choice for many ornamental plantings. Although these trees can be valuable for wildlife, they will not develop the range of organisms associated with native trees, but features other than their ecological value may have priority. Many street trees, avenues or groupings of ornamental trees may be far more important to the local community than trees or woodland which are ecologically more valuable.

Values include:

• Landscape and local identity.
• Screening and shelter. Trees may screen unattractive views, give privacy, shelter and shade.
• Environmental value, in reducing run-off, absorbing carbon dioxide, counteracting the ‘heat island’ effect of cities.
• Improving the appearance of and value placed on local areas.
• Botanical interest.
• Amenity and recreation. A wood-pasture, park, golf course or similar landscape of grass and trees is an ‘ideal landscape’ for many people.

The advice to plant small trees, and to keep them weed-free for at least three years remains the same, whether you are planting an individual tree or many hundreds. However, it may be more difficult to obtain non-native species, or particular cultivars of native species, as transplants, and they are more often sold as whips or standard trees. Fruit trees are normally grafted onto particular root stocks which limit the growth of the tree, and are sold as bush, half-standard or standard trees.

Species must be chosen with care, taking particular note of the space available and the recommended planting distances from buildings. The larger native species such as oak, beech, ash and small-leaved lime can achieve a spread of 20-30m (60-100’) when grown in open ground, and are only suitable for planting in very spacious surroundings. Smaller native or introduced trees may be more suitable than large native species for non-woodland planting, because they require less space.

Apart from street trees, nearly all these types of plantings are intended to result in well-spaced, clear-stemmed trees surrounded with grass. However, for successful establishment it is essential that the trees are not grown in a grass surround until they are about ten years old. Grass, and particularly mown grass, competes strongly with young trees, and mowers can damage or kill trees!

At the planning stage, you must take into account the management of the area between the trees in the decade or so after planting. There are various approaches given below. Whichever method you choose, the cost in time and money of the purchase and planting of the final trees is likely to be a small proportion of the amount invested in creating the conditions in which the young trees will flourish. However, the familiar sight of groups of long- planted but struggling trees in a grass surround is the reason this investment must be made.

Small groups of trees

One of the three following methods can be used:

• Plant the final trees amongst a matrix of shrubs or trees at a spacing of 2 or 3m, as for woodland planting. The final trees can be planted singly, or in groups of three or five, from which further selection takes place during thinning. in the first few years the thicket of growth will provide mutual shelter, and protect the final trees from damage by vandals or mowers. The shrubs and trees nearest to the final trees can be coppiced or removed after about five years to give the final trees space to spread. if the final trees grow up with too much competition, they will not produce sufficient side branches to make a balanced shape, nor sufficiently spreading roots to be stable when the other trees and shrubs are removed. Keep all the trees and shrubs weed-free by herbicides or mulches (Chapter 6 – Planting and protection), preferably keeping the whole area weed-free. If planting is at 2m spacings, the required 1m diameter weed-free area around each tree will anyway result in the whole area being weed-free. The thicket stage is valuable for wildlife, but blocks views and may not be popular with local residents. you also need to take into account the work involved in removing the unwanted trees or shrubs.
• Plant only the final trees, but keep more than the minimum 1m grass-free circle around each tree. A 2m grass-free circle using mulch, herbicide or surface cultivation will be repaid by significantly better tree growth. This method gives no protection to the trees from vandals, mowers or accidental damage, and the trees may need wire mesh protectors or similar. A large area of ground covered with plastic mulch or bare from herbicide application does not look attractive. A loose organic mulch, with or without residual herbicide or plastic mulch looks more acceptable, but is expensive.
• In school or hospital grounds, parks and large gardens, another approach is to surround the final trees with low-growing garden shrubs and ground cover plants. Even better is to plant into an existing shrub bed or border, where conditions will give trees a really good start. The young trees can unobtrusively establish amongst the shelter of the shrubs or other plants, safe from mowers and most vandals, and in soil which may already support beneficial mycorrhiza that do not occur under grass. Once the trees have grown to a significant size in their surroundings, the shrubs or other plants can be removed as required, and grass, bulbs or native woodland plants established amongst the trees. If making a new bed, choose cheap low growing shrubs such as spiraea or lonicera nitida, bought as bare-root hedging shrubs in winter. Berberis, dwarf gorse and other spiny shrubs are useful to deter access. Although the cost of purchasing sufficient shrubs may seem expensive, in the long term it may be cheaper in labour costs to have a low-maintenance shrub border, rather than mown grass, and it will certainly benefit the trees. Perennials, annuals or even vegetables can be grown in the bed as desired, as long as the tree roots are not disturbed during cultivation.

Arboreta, avenues and individual trees

Collections of trees in arboreta, street trees and other trees planted singly may need protection from accidental or intentional damage. Introduced trees and cultivars of native trees are normally planted as feathered whips or standards, which will need staking until the roots have established. Individual trees should have a weed-free surround of at least 1m diameter, and preferably 2m, until they are well established. Wire mesh or timber guards may be needed against vandals or grazing animals or.

Avenues are normally planted at their final spacing, and protected individually. However planting within a fenced strip in a matrix of shrubs or smaller trees as described above may be cost-effective.

See page 81 for details on planting standard trees.

Hedges and shelterbelts

Hedges for enclosure of stock are typically of species which are thorny and dense and respond well to laying and clipping, with hawthorn the most popular species. Hedges are normally planted in a double row, with rows 37cm (15”) apart, and plants 45cm (18”) apart in the row. Keep the entire base of the hedge weed-free until the plants are established. Many other native species can be used for hedging, and can be managed either by clipping, laying or coppicing. For full details see Hedging.

Shelterbelts are narrow bands of trees planted to give shelter for crops, stock, gardens or settlements. They need to be carefully planned with denser planting of smaller species on the windward side, to create a smooth profile which directs the wind up over the taller species behind, with a minimum of turbulence caused beyond.

Shelterbelts have long been used in upland areas, and some are ancient features of the farming landscape. Any replacement planting should take into account their historic, landscape and wildlife value.

The design of shelterbelts must allow for wind permeability in order to avoid the formation of eddies. For optimum efficiency, about 40% permeability is needed. A shelterbelt can create shelter for about 20 times the height of the belt on the downwind side, and about three times the height on the upwind side. The wind will sweep around the ends of the belt as well as over the top, leaving a triangular sheltered zone, as shown.

The base is the most important part of a shelterbelt, as if it becomes sparse, wind speeds are increased through the wood and into the area beyond. Remedying this situation is difficult because new plants cannot establish in such draughty conditions unless given artificial shelter.

Narrow belts, about 20m wide, are generally the most effective width for crop protection. Wider belts give no more shelter, and neither are they particularly suitable for timber production. The disadvantage of narrow belts is that they cannot be restored without clearing and replanting, and they are less attractive than wider strips as landscape and wildlife features.

The trees are usually planted using staggered or triangular spacing, so that they stand 2.4m (8’) apart along rows that are 2.1m (7’) apart. Each tree will then stand 2.4m (8’) apart from adjacent trees (about 1916 trees per hectare). For most purposes an a-shaped profile is suitable, with the middle third planted with tall trees and the outer third planted with smaller trees and shrubs.

Avoid gaps, openings and re-entrants on the windward side of shelterbelts. If an opening is needed, make it oblique to the wind and plant the edges with wind-firm species.

Where the aim is maximum shelter for minimum width, plant tall, wind-firm species up to the windward edge, with smaller trees and shrubs along the leeward edge. Conifers should normally be interplanted with broadleaves to give winter shelter and act as a nurse crop.

Suitable species for shelterbelts

Given the appropriate soil and climate, suitable species include the following:

TALL Lime, oak, sycamore, Scots pine
MEDIUM Whitebeam, cherry, rowan
SMALL Hawthorn, holly, hazel.

Establishment and maintenance

Three different approaches are outlined below:

• Nurse species can be planted, which will grow quickly and shelter the slower-growing, longer-lived species. Suitable conifers include Scots pine, and introduced species such as Sitka spruce, European larch and hybrid larch. In areas where rainfall reaches 75cm (30”) annually, willow and poplar can also be used as a nurse. The nurse trees can either be planted in a strip along the windward edge with an outer strip of understorey shrubs, or can be mixed throughout the planting. Both methods have drawbacks. When a windward strip is felled or deteriorates, the increased exposure may damage the remaining trees. Nurse crops which are mixed throughout need careful thinning and removal to make sure the slower-growing species are not swamped.
• The belt can be established in two stages, planting half the width initially, and the other half as the planting begins to mature and becomes sparse at the base.
• Plant the full belt initially and thin it heavily at about 15 years, and more lightly thereafter at about 5 year intervals. At the same time underplant with shade- bearing shrubs, small trees, or successor species such as beech.

It’s normally best to follow the example of similar successful shelterbelts in the locality. In coastal conditions for instance, plants which are generally tolerant of salt winds may not be so in every situation, and a tried and tested species is normally best. Some coastal localities are characterised by particular introduced species, such as holm oak, Monterey pine or tamarisk.

Old, sparse, ineffective shelterbelts can be revitalised in several ways. Where a belt casts a heavy shade, plant a new margin one to three rows deep along its windward edge. Then thin and underplant the old belt.Alternatively, replant existing gaps in the belt and then gradually extend the replanted areas by further fellings. A third method is to cut a series of V-shaped wedges through the width of the belt, starting at a point on the leeward edge. These should be replanted and progressively widened out by further fellings until the whole belt is gradually replanted.

Shelter for stock

In upland and exposed sites, woodland may be planted to provide shelter for stock.

Woods can be designed so that they offer shelter, whilst still being fenced. On open land where stock can move around the perimeter, blocks of woodland will give some shelter whichever way the wind is blowing. Some woods are planted in an l or X shape, to increase the length of edge. The permeability of the woodland is not significant, and any suitable species can be used.

Other woods for shelter can be partly or completely unfenced, allowing access for stock. This gives better shelter, but ground flora and tree roots can be damaged by trampling and browsing. Bark damage may occur, and natural regeneration may be prevented. A better method is to divide the woodland into three or four fenced compartments, using one per season in rotation. Additionally, natural regeneration can be protected by tree shelters.

Trees and buildings

Problems associated with trees around buildings include those both above and below ground. Above ground problems include the following:

• Blocking of gutters with leaves or needles. Species with large leaves, such as sycamore and large-leaved lime, can cause blockage if they overhang gutters.
• Obstruction of light.
• Physical impact of branches on a building.
• Interference with overhead services.

Underground problems include the following:

• Drain blockage. Usually, tree roots will only penetrate a drain if it is already cracked. The roots then tend to grow towards the supply of water. A single root entering the crack can branch enough times to create a blockage.
• Physical damage by root growth. generally, the major roots of a tree grow in a radial fashion from the stem base, within the top 30-50cm (12-20”) of the soil. Although roots can laterally extend as much as 1.5 times the tree’s height, most problems arising from the growth of roots will be located around the trunk of the tree. Common problems include paving being lifted or cracked, and walls being undermined.
• Damage from shrinkage of clay soils. Trees planted on shrinkable clay soils can dry the soil by removing water through their root systems. If any buildings are located nearby, subsidence of their foundations can occur. Deciduous broadleaved trees remove more water than evergreens and conifers. The table shows the minimum distances from buildings at which trees can be planted to avoid the danger of subsidence. Note that these are ‘safe’ minimum distances, as recommended by house insurers. Many existing urban trees are far nearer to buildings than this recommendation. However, with drought an increasing problem, it is suggested that these guidelines are followed for new planting in clay soils.