5.1 For Sawlog Production
In Britain today there is an annual consumption or 0.5 million hardwood sawlogs, which is insignificant when compared with that of other European countries such as France, which consumes 7.5 million sawlogs per annum. Table 14 shows that in 1980, 51 percent of the hardwood sawlogs used in Britain were home-grown, but 66 percent of these (see Table 16) were used for low value products. The Forestry Commission (1984) estimates that 40 percent of all hardwood trees have some millable timber volume. The results gathered in the current survey (Table 7) show that in the case of hedgerow oaks on this estate on the Wirral, this figure is an over-estimate. At most 27 percent might have some sawlog potential, and if roadside trees are excluded this figure falls to 19 percent.
Table 14: Sources of Hardwood Timber In Great Britain
Hedgerow trees generally produce short lengths of rough timber (Ward, 1954), but the occasional tree, especially large, isolated park trees do produce valuable boles. In exceptional cases even veneer quality timber might be produced. Table 15 shows the distribution of prices which might be offered for oak timber of varying standards. The vast majority of hedgerow trees fall into the lower two classes, and are used for fencing, mining timber or pallet construction. Extraction is often a problem on farmland (Ward, 1954), but unless trees are to be left to disintegrate where they stand they will have to be removed at some point.
Table 15: The Contents of an Average Oak Sawlog Parcel (Various Sources)
Where A is the value in £ -3 for mining / pallet timber
Table 16: Uses of Hardwood Timber Between 1980-85
Sawmills are extremely wary of accepting hedgerow timber due to the risk posed nails and barbed wire within the trunk. Most sawmills put the logs through a metal detector test before processing. If the log does contain any metal, it is rejected as a sawlog. Such logs are really only useful as firewood. Photograph 4 shows illustrates some of the typical problems in utilising hedgerow timber. Note the mishapen trunk which has shaded out the hedge below - the gap has been filled with barbed wire which has further lowered the trees timber potential.
Photograph 4: A Poor Quality Hedgerow Timber Used as a Fence Post
During the survey it was noted how tree form improved when the trees were closer together. There is, of course, nothing new in this observation, but it tends to support the proposals of the Countryside Commission (1974; 1984). These proposals recommend that future tree planting should not be of isolated trees, but of groups on otherwise unusable land. This would result in the trees being of better form and greater timber height. Other benefits would include easier management and a reduction of foreign bodies, such as fencing materials, within the timber. It would also reduce harvesting problems. A management scheme such as this would mean that some form of rotation for farmland trees could be practised.
Photograph 5: Poor Pruning and Lopping are Conspicuous on Many Farmland Trees (Countryside Commision, 1984)
In terms of the Lever-Hulme Estate, it is difficult to make any specific recommendations, as the management of hedgerow trees is left to each individual tenant farmer. The condition of the trees and therefore the number which might have some potential for sawlog production is likely to decline the longer the trees are left unmanaged. It is possible that a replanting scheme of the kind described earlier could be started, while leaving the over-mature trees standing and undisturbed.
If the present condition remains unchanged it is possible to envisage in the long term (perhaps in another 100 years) the loss of all large oaks with very few young trees to replace them.
5.2.1 Hedgerow Trees As A Source Of Fuel
In the past hedgerows provided a significant supply of timber to the domestic fuelwood market (Rackham, 1977). Today, according to Forestry Commission figures, over 100 000 wood-burning stoves have been sold by the year 1980, and some interest has been expressed about the possibility of increasing the use of wood as a source of energy (Crowther et al, 1980). As the majority of hedgerow oak trees are over-mature and due for felling, it might be worth considering their potential to supply this market.
5.2.2 The Potential of Wood As Fuel
A wood burning stove will consume an average of 7 tonnes of wood per year (Krebs et al, 1981). The wood should be air-dried to a moisture content of at most 23 percent before use. Green wood has a positive calorific value and its use leads to a 25 percent loss in efficiency (Aaron, 1975). Table 17 shows the approximate price that wood would have to be sold for if it were to compete with other fuels. The figures quoted have been adjusted to 1987 wlues by assuming an average inflation rate of 5 percent for fuel prices.
Table l7: The Maximum Price Per Tonne of Wood if it Were to Compete With Other Sources of Energy
(Source: Aaron, 1975)
5.2.3 Some Drawbacks In Using Wood As Fuel
Wood requires a much larger storage space than other forms of fuel. For example, 1 3/4 tonnes of air-dried wood will occupy about 4 cubic metres when stacked. This is equivalent in heat production to 1 tonne of coal, which occupies 3/4m3. Wood bought in a green state will require an even larger storage space in order to dry out (Aaron, 1975). Wood is labour-intensive to prepare and stack. Its use as a fuel is prohibited under the Clean Air Act of 1956 in any area where smoke control is in force, unless a specially designed stove is used (Aaron, 1975).
5.2.4 Hedgerow Oak Trees On The Wirral As A Source Of Fuel
By extrapolating from the sample data it would seem that there is about 4 650 m3 of timber within the survey area. This would be sufficient to supply around 30 wood burning stoves for the next 20 years, which is roughly one stove for every farm in the area. After considering this, the prospect of selling the timber profitably becomes fairly remote. As with sawlog production the extraction problems caused by widely scattered trees must also be considered.
1t an intensive replanting programme were instituted, the best management would be that suggested for sawlog production (see Section 5.1). Such a plan would lead to a more controlled production of both sawlogs and branch wood - which could be used as fuel. The profitability of fuelwood sales is still likely to be marginal despite this improvement.
5.3 As a Habitat For Wildlife
The oak tree is famous as a habitat for many insect and bird species. Indeed the oak has been found to support 284 species of insects (Moore, 1968), which is more than has been recorded for any other tree species. Compared with other tree species it ranks fifth in regard to the numbers of bird species eating its fruit. However, Krebs et al (l981) point out that the number of insect species supported is not sufficient evidence that oaks make the beet habitat for birds. One study carried out by them concerned stands of single tree species of oak, ash (Fraxinus excelsior), sycamore (Acer psuedoplatanus), silver birch (Betula pendula) and larch (Larix spp.); the numbers of species of birds using each stand was recorded and it was found that the larch stand was used as much as any other stand, although it was the most recently established species. Despite this oak remains the most commonly planted species throughout 37 counties (Krebs et al, 1981).
The Countryside Commission (1974) recommends that any new tree planting on farms should be other on land too difficult to cultivate or in field corners or near buildings and along roadsides. In general new planting seems to be following these guidelines, with only 13 percent of all new trees being planted in hedgerows (Krebs et al, 1984; Countryside Commission, 1984).
Studies have shown that the larger the area that an area of woodland occupies, the more bird species it can support. A group of trees as described above is thought to be more beneficial to birds than single trees along a hedgerow (Krebs et al, 1981). The recent EEC Green Paper in the Common Agricultural Policy suggests that large areas of farmland should be taken out of production in order to reduce food surpluses. The most likely result of this action would be that large areas of farmland will revert to forestry, while the best land will still be farmed intensively, rather than a larger area farmed 1ess intensively (Green, 1986). These changes will not halt the decline of the hedgerow oak, but the numbers of oak trees in plantations would probably increase. Only time will show that happens to the face of the British Countryside if these proposals are implemented.
© 1987 Robert I. Bradshaw