Book: Fencing Chapter: 9 Fencing ­- special uses Section: Tree protection Metadata: Details Buy this book

Tree protection may be required for the following:

1. Individually planted trees.
2. Newly planted woodlands.
3. Newly cut coppice, to allow successful regrowth.
4. Existing woodlands, where browsing is preventing the natural regeneration of trees. Grazing may also damage woodland ground flora.

The damaging agents to trees include:

1. Stock. Nearly all types of stock will damage young trees by trampling and breaking them, pulling them out of the ground, browsing on the leaves and shoots and stripping the bark. Damage is worse when other grazing is in short supply, but can happen even when there is plenty of grass available. Mature trees are normally safe from damage, but horses may strip the bark.
2. Wild animals. Deer and rabbits are a severe problem to young trees, and in many parts of the country, tree planting or regeneration is impossible without protection. Voles may also be a problem, as they chew the bark at the base of newly planted trees. Treeshelters, tree guards and other types of individual protection are widely used for protection against deer, rabbits and voles, and can be used to protect naturally regenerated seedlings. For larger areas, perimeter fencing becomes the cheaper option. Perimeter fencing also protects the ground flora, but total exclusion of trampling and grazing may also have an adverse effect on woodland ecology.
3. Vandalism, accidental damage and trampling can occur on any sites where the public has access. In many situations, treeshelters give sufficient protection, but in some places where vandalism is a problem, more substantial guards or fences are needed. Individual trees are most at risk, especially in parks, pedestrian areas and roadsides. For groups of trees or new woods, the density of planting, size of planting stock, management of ground vegetation between the trees and the involvement of local people will have a strong effect on whether vandalism or accidental damage occurs. For further discussion of this subject, see The Urban Handbook (BTCV, 1998).
4. Mowers and strimmers, even in the hands of experienced operators, are the frequent cause of damage to young trees in parks and open spaces. Wounds to the bark weaken the stem, lessen growth and allow disease to enter. Fences or guards that prevent damage are worth installing around vulnerable trees. Note that mown grass should never be used as a way of managing the ground surrounding newly planted trees, because growth of the trees will be severely affected by competition from the grass. Herbicides, mulches or hand weeding must be used to keep the ground clear. For further details, see Tree Planting and Aftercare (BTCV, 2000).

Fencing is not the only method of protecting trees, and for deer and rabbits, control of population may be a better option. Squirrels also severely damage trees by bark stripping, especially 10-40 year old beech, sycamore, oak and pine. Some areas have squirrel and deer management groups, co-ordinated by the Forestry Commission or the Deer Initiative, which control populations by various methods.

Tree protection is described below under three different types: woodland fencing, exclosures for individual trees, and tree guards. Tree guards are usually used in association with one of the other types of protection.

WOODLAND FENCING

Specification

Fencing represents a high proportion of the cost of tree planting, woodland establishment or woodland regeneration, with deer and rabbit fencing particularly expensive. It's important therefore to obtain as much local knowledge as possible to establish the likely levels of damage.

Examples of deer and rabbit fencing are given in chapter 1, with further information later in this chapter.

Nearly all wooded areas, even quite close to urban centres, will have populations of deer and/or rabbits. New planting
>or natural regeneration within or near an existing wood will almost certainly need protection. The cost of perimeter fencing needs to be compared with the cost of individual protection. The following factors need to be considered when balancing this equation:

1. The cost of individual protection (expressed as £/tree), and the cost of fencing (expressed as £/metre).
2. The size of the area to be planted.
3. The shape of the area to be planted.
4. The planting density, or the density of natural regeneration to be protected.
5. The public use of the area and the likelihood of damage or vandalism.

An example, for roe deer, is shown in the graph below.
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The preceding table gives an example calculation for cost-effective tree protection. Both the graph and table are from the Forestry Commission Practice Note 3 The Prevention of Mammal Damage to Trees in Woodland (Forestry Commission, 1998), which should be consulted for further details.

Where individual tree protection is used, fencing against stock or people may also be needed. Specifications for cattle, horses and sheep are given in chapter 1, with details on goat fencing on special uses.

Fencing to exclude public access will depend on the circumstances. In areas of habitual public access any fencing or planting which infringes on customary local use is very likely to be damaged. Tree planting areas and associated fencing must be carefully planned to avoid informal paths, short-cuts, places where children play football or where views may be obscured as trees grow.

Where vandalism is a problem, fences that are difficult to climb will be some discouragement, but any strained wire or wooden fence can be vandalised. Barbed wire should act as a deterrent, but is easy to cut. Chestnut paling may be effective. Thorny shrubs or bramble may be a useful barrier in addition to a fence. Traditionally, small woods were enclosed by a hedge of thorny shrubs, which was laid to keep it stock proof.

Shape of woodland area

The plan of the fenced area is important in determining the cost of the fence per unit for the total area enclosed. Simple shapes, with long straight runs and the minimum number of straining and turning posts are the most economical.

Ground plans of fences, in order of cost effectiveness, are firstly squares, then rectangles, triangles, and finally complex shapes. However, straight lines and regular shapes to enclose new woodlands can be visually obtrusive, especially on rising ground. Varying the planted area within a regular shape, and planting trees outside the main fence help break up regular outlines and give a more natural appearance to new woodlands (see design and siting).

Small woods and groups of trees

Individual tree surrounds are a very expensive way of protecting trees from browsing animals, and do not provide the best conditions for tree establishment. Reasons include:

1. The tree will lack shelter.
2. The tree is more likely to suffer from competition from surrounding grass than are trees that are planted in a group.
3. Individual trees and surrounds are frequently targets for vandalism.
4. By planting only one tree you are not only inviting failure for the reasons above, but you are not providing an alternative. By planting a group of trees, it is much more likely that at least one will survive to maturity.

Where young trees are planted close together, they mutually shelter each other, and early canopy closure prevents grass growth and helps rapid establishment. If the desired outcome is a small group of oaks, beech or other trees, success is much more likely if these are planted amongst a mixture of other trees and shrubs, with the whole area fenced off. The unwanted trees are thinned out at a later stage, and the fence removed as required. An example is shown below of an area which could be planted with about 70 young trees and shrubs at about 3m (10ft) spacing, which are successively thinned to leave about 7 trees to grow on to maturity.

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Removing animals from an exclosure

Any rabbit warrens within fenced areas will have to be destroyed before the fence is constructed. A deer leap or sheep ramp (see gates and stiles) should be included, so that any deer or sheep which get into an exclosure, for example after heavy snowfall, can find their own way out. A gate should be included to give access for management, as well as for removing animals that find their way in.

FENCING INDIVIDUAL TREES

This is an expensive way of protecting trees, and is not the best way to encourage successful establishment (see above). Always first consider instead planting a small group or band of trees, which are later thinned to leave the desired number. Individual tree protection may be appropriate for newly-planted trees in parkland, commons and wood-pastures, or for protecting natural regeneration in woods, wood-pastures and other areas.

Consider the following:

1. What is the reach of any animals to be grazed around the tree? Unless it is certain that only sheep will be grazed on the land in the following years, it is usually worth providing fencing for horses or cattle, as a single animal can destroy several years' growth, or kill a tree by debarking it in just a few hours. See the tables below. >

Table 9.2 shows the height of the guard required against various animals, and the distance it should be from the tree. In zone A, the barrier must be of netting or timbers which are close enough to prevent the animal putting its head through and reaching the tree. In zone B, the barrier need only be sufficient to prevent the passage of the animal. The spacing of the horizontal and vertical members of netting or timber are shown in Table 9.3. Note that in Table 9.2, for most animals the height of the barrier decreases with distance from the tree. However, against deer the height of the barrier increases as the distance from the tree increases. This is to prevent deer jumping into the exclosure.

1. If deer or rabbits are a problem, it might be more economical to build a stock proof surround, and then protect the tree against deer and rabbits with a treeshelter or tree guard.
2. Failure rate of single trees in exclosures is high. Build the exclosure so that it is possible to get inside it to replant as necessary. Removable sections or netting which can be folded back may be necessary.
3. Consider using a herbicide or mulch to kill all ground flora within the surround. This not only greatly aids the growth of the tree by reducing competition for water and nutrients, but also reduces the pressure on the fence from grazing animals, as they have less inducement to lean through.
4. If a herbicide or mulch is not being used, you will need to make the surround accessible for hand weeding.
5. It is not possible to build an exclosure simply out of three or four posts with strained wire or netting, as sufficient strain to keep the wire taut will cause the posts to move. Horizontal rails, preferably rebated, must be included.
6. All sorts of stock may use the exclosure for rubbing against, so build it strong enough to withstand this, with horizontal rails as shown. Sheep and cattle may also tend to shelter in the lee of the exclosure, causing soil erosion at the base of the fence, which may then need extra wires to keep it stock proof.
7. Once the leading shoot is safely out of reach of animals, the tree is safe from damage by browsing. A smaller diameter guard which protects the bark from stripping and other physical damage may be suitable (see below), and could replace a larger surround which may be suffering from wear and tear.

Designs

The first design is proof against sheep, and against cattle in most situations. Note the rails, to keep the posts in position and prevent the wire slackening. A plastic guard can be used against rabbits and voles.

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The second design has rabbit netting around the lower section, and is proof against all likely damaging animals, except voles and squirrels. Attach one end of the upper netting by twisting the wires, without stapling. This allows the section of netting to be rolled back to give access for tending the tree. A heavy-duty mulch mat that covers the enclosed ground area is recommended for weed control, or alternatively a herbicide can be used. This type of surround, which excludes browsing animals by height, rather than by reach, tends to be the most economical design. Its cage-like appearance can look rather unattractive.

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The fencing surround against horses and cattle, shown below, is expensive in materials and takes up a large amount of ground area, but may be preferred because of its appearance. A plastic guard against deer, rabbits and voles can be added as necessary.

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Triangular shaped exclosures for single trees are suitable against sheep, but not other stock. However, once the leading shoot has grown out of reach of browsing animals, the type of surround shown below may be suitable for protecting the trunk. Carefully dig a shallow pilot hole at each post position before knocking posts in, so that any large surface roots can be avoided.

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To protect individual planted or naturally regenerated trees in wooded areas against deer, a simple ring of deer netting can be used, secured to the ground with two stakes. These are not suitable for places where cattle, horses or sheep graze, as they will damage the surround. Some damage from deer may also occur if grazing pressure is high, and the surrounds are not vandal-resistant. Use a 3.6m (12') length of deer netting (eg 13/190/15 or 11/155/15 depending on deer species) joined back on itself by twisting the wires. Secure it to the ground with 1.8m (6') x 50mm (2") square stakes or similar, attached to the netting with lengths of wire.

Where rabbit damage is also likely, fit a suitable guard to the stem of the tree before erecting the deer netting surround. Alternatively for multi-stemmed growth, hexagonal mesh can be attached to the deer netting, but it is not easy to fit this with a lapped edge to prevent burrowing.

TREE GUARDS

There are a huge range of treeshelters and tree guards available on the market, a few of which are shown below. Spiral guards prevent bark stripping by rabbits and hares. Treeshelters and mesh guards protect young trees from bark stripping and browsing, and also enhance growth by providing a sheltered environment. Solid shelters, of polypropylene or polyethylene, provide the most enhancement to growth, and give useful protection against herbicide damage when weeding. However they may produce tall, spindly growth, and can harbour voles, or collect rainwater that may freeze. Mesh guards give more aeration and promote better wind resistance, but give less upward growth benefit. They are usually slower to fit. Degradability is very important if the treeshelters or guards are not to be removed by hand.

Guards and shelters must be chosen carefully to fit the type of planting stock, and to be effective against the damaging animals in the area. Spiral guards, for example, cannot be fitted to multi-stemmed plants such as hazel. Shrubs can only be protected by wide diameter shrub shelters. If browsing animals can reach the top of a treeshelter, the young tree will be constantly browsed at that level.

Treeshelters and guards must be properly installed. Most types attach to a stout wooden stake, as recommended by the manufacturer. Canes do not provide sufficient anchorage. The growth enhancement provided by shelters is of far less importance than is effective weed control. Contact suppliers for further information.

Treeshelters and guards are available in the following heights to be proof against the animals listed.

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ANIMAL HEIGHT OF GUARD

Vole 0.2m

Rabbit 0.6m

Hare 0.75m

Roe and muntjac deer 1.2m

Sheep (small breeds) 1.5m

Sheep (large breeds), goat 1.8m

Red, sika and fallow deer 1.8m

The cost of using treeshelters, guards or other individual protection needs to be balanced against the cost of erecting a perimeter fence. Other factors such as site access, vandalism and ease of herbicide application also need to be taken into account when balancing the equation.

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