The Wessex group of the Institute of Foresters held five field meetings in 1980 with the object of examining the current place of ash in the silviculture of the region. Woodlands were visited at Cirencester Park (Gloucestershire), Norman Court and Lockerley (Hampshire/Wiltshire), Garnons and Park Wood (Herefordshire), Savernake (Wiltshire), and Bowood (Wiltshire). A number of questions were raised, and a few of these were answered.
One of the classic silvicultural texts (Busgen and Winch, 1929) refers to an earlier paper (Winch and Dieterich, 1925) in which marked genetic differences were found between ash from dry calcareous sites and ash from moist clayey sites, giving the impression that there are distinct 'lime ash' and 'water ash' types. However, any such distinction is likely to be rather blurred, as any very clear division would tend to be followed by a division into separate species, as in the case of oak (Quercus robur L. and Quercus petraea Liebl.) and birch (Betula pubescens Ehrh. and Betula pendula Roth.); and this does not appear to have happened in the case of ash.
Leibundgut (1956) and Weiser (1974) also looked for differences between progeny of trees fromdifferent site types but were unable to find any. More recently, Patlai (1976) claims to have found some differences, in a series of 41 year-old trial plantings of ash from 51 areas in the Ukraine. Increment of ash from damp areas was less than that of ash from drier areas.
Nothing was seen on any of the field visits which gave any indication of the existence of different ecotypes in this part of England. Differences in growth rate, form, and quality could probably be explained in terms of soil type, availability of moisture, and silvicultural treatment; and this view is supported by experimental work carried out in Tintern Forest (Gwent) reported by Nimmo (1961), where no difference was found between the growth of ash from several parts of Britain, covering a wide range of soil types. The test site in this case was however a good site for the growth of ash, and it is possible that the selection of suitable strains may be more important on difficult sites, where ash may be grown primarily for amenity, shelter, or wildlife rather than for timber production.
As with ecotypes, the question of the potential for genetic improvement of ash for increased vigour, better quality timber, or disease resistance remains largely unanswered. Very little work appears to have been done on this species, which is not one of the species covered by E.E.C. regulations.
One factor which did re-emerge in our examination was the tendency for male or predominantly male trees to be of better form than predominantly female trees, and there is therefore a tendency to remove potential seed-bearing trees when thinning a stand, leaving only male trees. If seed is required, it may be necessary to leave some trees of poorer shape when marking, if these can be seen to be seed-bearing.
There appear to be no known instances of F. excelsior hybridizing with other timber-producing species of ash such as F. americana.
No serious disease problems were seen. Canker was present in some stands, but is rarely very troublesome on sites where ash grows well. Its incidence may be increased by physical damage caused by friction between trees in windy weather, or by rubbing of brambles against saplings.
No examples of 'die-back' were seen, except in situations where the felling of adjacent stands has left trees suddenly exposed to the wind. Ash bud moth may affect the leading shoots of trees up to about 5 metres high causing forking. This type of damage may be confused, at a later date, with the effects of late spring frost. In neither case is there any clear remedy, except, perhaps, to delay thinning until the trees are more than 5 metres high, thus giving a greater choice of stems.
Ash is almost entirely free from damage by grey squirels, and for this reason is a valuable component of woodlands in lowland Britain, particularly in woodlands where the other trees are mainly beech or sycamore, which are badly affected by this pest. Ash forms a valuable 'insurance' component in such cases, in the event of a severe attack by squirrels.
Unfortunately, ash is not immune to damage by rabbits, hares, and deer, the latter finding it particularly palatable; but where regeneration is copious and browsing is not very heavy some trees are likely to remain undamaged.
A pure ash crop does not make very full use of a site. The crowns have fairly brittle branches which break easily during gales, leaving a clear space between adjacent trees. This effect, together with the relativelysparse foliage of ash trees, results in a considerable amount of the available light being unused. On suitable sites, a pure ash crop will normally produce a greater annual increment of timber than oak, and less than beech. In mixture, the total volume production may be somewhat greater, if the mixture allows greater overall utilisation of the site.
Ash does not compete well with grasses when young; and older saplings and trees require crowns free from competition with other trees if they are to make good growth and give timber of good quality. Trees with very small crowns have difficulty in responding if given more room in which to grow. It is desirable to maintain a live crown of at least one third the height of the tree at all times. Stands were seen where the first thinning of natural regeneration had been left until the trees were utilisable for firewood, to avoid unremunerative thinning, but in some cases this can produce trees with very small crowns and poor vigour. A method of carrying out thinnings in regeneration more than 2.5 metres high has been described by Garfitt (1963), whereby the crowns of selected trees are freed from competition and the rest of the crop is ignored. Examples of crops where this had been carried out were seen at Cirencester Park, but there was not full agreement that this was always themost economic method of treatment. Where regeneration is very dense it may be sensible to reduce its density in some way at an early stage, at a height of about 1 to 2 metres, in order to avoid the need for costly thinnings when the stems are between 2 and 7 centimetres diameter.
In contrast to the dogma of recent decades, it is now generally accepted that ash timber with anything between 4 and 16 rings per 25 millimetre is likely to be suitable for most purposes. Timber with 6 to 10 rings per 25 millimetre is slightly stronger than timber outside these limits but only marginally so (Building Research Establishment, 1972). Timber which is grown faster than 4 rings or slower than 16 rings per 25 millimetre is likely to be unacceptable for the more specialised markets such as sports goods or tool handles, but within these limits the main differences will be due to the presence of knots, flutes, and other features.
The Forest Products Laboratory (1966) found no marked regional differences in ash timber, the main differences being between trees on any one site, with large-crowned knot-free trees with cylindrical stems being clearly the best. Timber quality in older trees, which have passed their peak rate of growth, tends to fall, with the production of wood of:low density and strength, and 70 years appears to be a reasonable rotation for this species (Devauchell and Levy, 1977).
Only a small proportion of ash stems are completely 'white'. Most have a certain amount of dark colouration in the centre. Although this rarely affects more than 20% of the timber volume it can reduce the value considerably. Strength properties are not affected, but the dark colour is disliked by the timber trade. Some sites appear to be more prone to this dark colouration than others.
Ash is a very versatile timber, being used, for example, in furniture, brush and tool handles, hockey sticks, turnery, and for cleaving into tent pegs and hurdles. It has a low moisture content when felled, which reduces the cost of handling, per cubic metre. It is, without doubt, the best timber for firewood, being light to handle and easy to split; and, having a low moisture content, it is ready to burn almost at once. It should, however, be sold by the trailer load (that is, on a volume basis), as is common practice in the firewood trade, and not over a weighbridge, or this advantage will be lost to the merchant. This versatility means that all sizes from about 7 centimetre diameter upwards are saleable, and that thinnings can be done at little or no cost even in fairly small sized material. The proportion of the tree which is sold for timber, rather than firewood, is higher in ash than with other common hardwoods; although this may change if the price of firewood increases markedly. Timber prices are generally higher than for comparable beech, but not as high as for the very best quality large-sized oak. In general, a mixture of ash in an otherwise pure oak or beech woodland is likely to increase rather than decrease the value of the stand.
Successful mixtures were seen where ash had been grown with oak, the ash being removed after 60 years to 80 years leaving the oak to grow for another 40 years or so. Successful mixtures were also seen where larch had been planted as a nurse crop, to be removed at about 30 or 40 years. Ash, beech, and sycamore, often naturally regenerated, also appeared to be manageable in mixture. Few examples of mixtures with evergreen conifers were seen, but there is no obvious reason why ash should not play a part in mixture with conifers, if suitably managed, particularly on sites where the conifers are not fully windfirm, and where a mixture of ash would give greater stability to the crop.
Unlike many tree species grown for timber in Britain, ash is native to this country and, as was seen at Park Wood (a Site of Special Scientific Interest in the Wye Valley, belonging to the Courtfield Estate), it can be of value in helping to conserve our native flora and fauna. It may not carry as many different species of insect as oak or willow, but the general assemblage of plants and animals found.in an ancient ashwood is likely to contain several species which are rare or of particular interest for nature conservation.
Ash requires a reasonably base-rich and moist soil with a high available nitrogen content in order to grow well, and is therefore not suited to heathland areas or to most of our upland forests, except in local areas of better soil. However in most lowland areas it grows and regenerates freely, making it particularly useful in woodlands managed on an uneven-aged basis and in woods which are too small or awkwardly shaped to protect easily against rabbits, squirrels and deer. In such cases, dense natural regeneration often stands abetter chance of success than expensively protected planted trees. On any site suitable for growing ash timber it should be possible to obtain natural regeneration with the minimum of effort; and on sites where Clematis is a problem ash has an advantage over many other species, as it is often able to grow clear of the Clematis, where other species become bent over and smothered.
Pure ash woodlands occur naturally in some parts of northern and western Britain, being a feature not found in other parts of Europe, where beech and silver fir occur. These semi-natural woods have a certain charm; but pure ash plantations often appear unthrifty and unimpressive to the eye.
Bearing these points in mind, the Group are of the opinion that ash has a definite place in lowland forestry, but usually as a component of a mixed crop rather than a pure stand.
Where a site is suitable for ash, but none are present, it is suggested that a few should be included in any planting to act as potential seed bearers for the next rotation. The plants should preferably come from parent trees which are of good timber quality, and preferably from within the same region.
More work needs to be done on the selection of high quality parent trees, on the effects of delay in thinning dense natural regeneration, and on the use of ash in mixture with evergreen conifers. It would also be interesting to investigate the volume and value of timber produced by mixed crops containing ash, as compared with comparable crops of single species.
The place of ash (Fraxinus excelsior) in lowland silviculture was examined during the course of five field meetings. Ash is a native species producing valuable timber and regenerating freely. No major problems of pests or disease were evident. Although the volume of timber produced is not as high as with most coniferous species and some exotic broadleaves, the Group saw a definite place for ash as a major component of mixed woodlands in lowland Britain.
This report is based on notes and comments from several members of the Wessex Silvicultural Group, in addition to general discussion involving all members. The paper by Patlai was translated by N. de Berker.
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