Walnut - Juglans regia & J. nigra
Walnut is without the question the most beautiful wood on earth, ranging from the colour of honey to the rich depth of chocolate-brown, often marked with smoky swirls and streaks of pigment from dark brown to black. The grain can be perfectly straight, elegantly swept, or a festival of waves, curls, mottles and motes, sunburst and fiddleback, as intricate as an opium dream (McIntosh 1995).
Why grow walnut for timber?
The common or English walnut (Juglans regia) is one of the ancient introductions to Britain but today there are probably fewer trees than at any time since the late sixteenth or early seventeenth centuries. Interest in walnut as a timber waned with the increasing availability of tropical hardwoods from the early nineteenth century onwards and it has been infrequently planted since that time, particularly as a forest tree. Supplies of hardwoods such as mahogany are now, nearly 200 years later, becoming scarce. There is also an increasing awareness by European consumers that the use of tropical timbers may contribute to deforestation, resulting in a reluctance to buy them. There are therefore good reasons to believe that valuable, decorative, temperate hardwoods are likely to be in much greater demand as tropical supplies decline.
Walnut is perhaps the finest of these valuable species, and is seen as a tree that could regain the place it had centuries ago, as the provider of high quality timber on relatively short rotations. The wood is used for making quality furniture and producing highly figured veneers, usually from burrs, which are used for cabinet-making and decorative panels. At present however, walnut is often overlooked by foresters due to its reputation as being a species which is site demanding, usually of poor form and which suffers badly from the effects of frost.
To encourage a revival of interest in walnut (Juglans regia) in Britain, desirable straight stemmed and finely branched trees to suit the climatic conditions of the country have been selected from suitable parts of the species' natural range (see below). The tree phenotypes seen in Britain today are often of poor form for timber production because their likely origin is from European trees originally selected for nut production. Phenotypes for timber or nut production are generally viewed as incompatible because good phenotypes for timber (e.g. long and straight stemmed, finely branched) have deliberately been selected against. Short-boled, spreading and branched trees (such as in the picture above) were sought for high nut productivity and ease of harvesting. Additionally, some phenotypes in Britain may originate from ancient introductions, taken from environments unsuitable for widespread introduction to the British climate.
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Walnut Species
The Juglandaceae is a large family containing seven genera and approximately 60 deciduous, monoecious trees. In addition to the genus Juglans L. (walnuts), the family includes Carya Nutt. (pecans and hickories), Pterocarya Kunth. (wingnuts), Platycarya Sieb. & Zucc., Engelhardia Lesche. ex Blume, Alfaroa Standl., and Oremunnea Oerst. There are 20 species in the genus Juglans which are grouped in four subgenera; Juglans Mann., Trachycaryon Dode ex Mann., Cardiocaryon Dode, and Rhysocaryon Dode. Juglans regia is the sole species within subgenus Juglans, characterised by a four-celled nut, a husk which separates from the nut at maturity, and seedlings which exhibit two rows of scale buds immediately above the cotyledons and below the spirally-arranged compound leaves.
Juglans regia has many common names, among them the Carpathian, French, Persian and Himalayan walnut, although today it is commonly known as the English or Common walnut. It is one of two walnut species more commonly grown in Britain, the other being the black walnut, J. nigra L. (subgenus Rhysocaryon), which is native to eastern North America. All walnut species produce edible nuts but many are encased in thick hard shells, a disincentive to commercial production, so the thin shelled J. regia is most widely cultivated for nut production.
Juglans regia has a wide natural range from Turkey in the west to Nepal and China to the east but is an introduced species to all of Europe.A range-wide collection has been undertaken by the Northmoor Trust which concentrated on Kyrgyzstan.
The origin and history of walnut in Britain
Palynological finds of pollen and macro-fossils of Juglans species have been identified across Britain, from Kirkcudbright on the west coast of Scotland, to Norfolk in the east, and Somerset and Devon in the south. Many macro-finds have been made including remains of walnuts at Roman sites in London, charcoal remains at Rotherley and remains in the sewers of mediaeval Plymouth. There is no evidence that walnuts were actually grown in Britain in that period and all pollen records point to Juglans appearing from 2000 years BP (before present); therefore it is classified as an introduced species.
Walnuts were widely grown in Britain by the sixteenth century but there is evidence from an Anglo-Saxon glossary that they were cultivated from as early as the eleventh century. The common name for walnut over the following centuries was based on 'walsh nutte' which referred to the Roman origin of Gaul and Italy, as opposed to the native hazel nut. There are several accounts in the thirteenth and fourteenth centuries that refer to 'great nuts', 'walnottes' and 'Walsnotes', including the writings of Chaucer.
The earliest description of walnut silviculture came from Gerard in 1597 who wrote:
'The Walnut tree groweth in fields neere common high waies in a fat and fruitful ground, and in orchards; it prospereth on high fruitful banks; it love not to growe in waterie places'.
During the seventeenth century there are frequent accounts of the use of walnut for timber. In 1678 Evelyn encouraged the planting of walnuts through his writings, and planted his own trees in a family estate at Godstone, reporting in his diary that many of his friends in Surrey were making a great deal of money from walnuts and that thousands had been planted locally. Evelyn also promoted the more widespread use of walnut for making chairs, tables, cabinets and other furniture, reporting that the more 'vulgar' beech was commonly used but disguised as walnut by staining it with a dye made from crushed green walnut husks.
During the 1800s walnut was widely planted and locally common in Surrey, Hampshire and other parts of south-east England but by the latter half of the nineteenth century its popularity was waning, probably due to the gradual increase in the availability of mahogany, introduced early in the century from the West Indies. There was still a demand for walnut timber used in gunstocks and for coach building (Roach 1985) but according to Marshall (1803) the timber was generally going out of favour:
'[mahogany superceded walnut] in the more elegant kinds of furniture; and beech, being raised at less expense ... and being worked with less trouble, has been found more eligible for the commoner sorts'
The advent of the Napoleonic Wars had a great impact on the walnut plantings in Britain as the timber was in immense demand for gun and pistol stocks and, as the number of suitable trees dwindled, prices increased dramatically. The high prices offered for the timber coincided with increased payments for agricultural products and this combined effect dissuaded most landowners from replanting.
In Britain today, Juglans regia occurs as single specimens or in small groups, and in these categories the species is rated as 'common'. In the most recent census of woodlands and trees in Britain between 1979 and 1987, no instances of J. regia or J. nigra were recorded. It could be that J. regia was overlooked due to its close resemblance to ash. Mitchell (1976) reported that in Britain there were no mature trees remaining with good straight boles as these were removed for timber, although a fine 27 m tall park specimen was blown down in 1975, and that the tallest remaining trees in Britain were about 21 m tall. He also reported that two trees with girths of 4.6 m were lost a few years before that time and that few trees of the same girth remained in the country.
Walnut timber properties
'Walnut is hard and strong, stable, lightweight, shock-resistant, flexible…. It shrinks and swells less than almost any other wood. It's sweet to work, lovely to smell, delightful to handle, and takes a splendid finish.' (McIntosh 1995).
Walnut sawnwood is used in high class and decorative joinery for furniture and tableware, and also in decorative construction work such as in churches, houses, banks and other public buildings, to which it is eminently suitable due to its strength and durability. Walnut was one of the finest timbers used for aeroplane propellers in the earliest days of aviation. A large furniture-making industry based on walnut exists in Italy but the high cost of the timber restricts its use in joinery, such as for door and window frames, to a relatively small market.
Veneer timber, for which a requirement is usually a pattern of some kind, is selected from the very best elements of the round timber and typically comes from the root crown or from branch and fork areas, termed 'crotch walnut'. The most valuable veneer timber comes from walnut burrs that are occasionally found on large trees. Harvesting walnut trees nearly always involves uprooting the tree with the root ball still attached. This allows the most valuable timber, at the root crown, to be fully utilised. Major markets for walnut veneer are in the furniture and the car manufacturing industries. Walnut has been widely used in gunstock manufacture where it is generally regarded as the best timber because it is excellent for holding metal parts and also shock-resistant, lightweight and highly decorative.
The value of walnut sawnwood and veneer logs is substantially greater than other broadleaved species. Eastern European walnut prices in 1990 were double those of oak for both veneer and sawn timber. Prices paid for walnut logs in Germany between 1978 and 1986, ranged from £90 to £1100 per m3. There is often great variability in prices paid for walnut timber due to huge variations in quality, difficulties with supply and poor marketing strategies. Up-to-date prices paid for walnut in Britain are difficult to come by as the timber is sold on a tree-by-tree basis, with prices varying according to size and quality. Recent (April 2000) timber prices in Italy, which consumes 50 % of the walnut veneer sold in Europe, started at £700 /m3 for minimum veneer grades (minimum length 2.2 m/ diameter 40 cm), whilst prices for good veneer grades range between £1000 and £1100/m3 but can reach much higher values for the best veneer grades. Decreasing volumes of walnut timber available on the European market, combined with an increasing demand for valuable wood products in general, are likely to inflate prices in the future.
The need for walnut research
Walnut is a species well known to be exacting in its site requirements with suggested latitudinal limits of between 44 and 54 °N for successful cultivation, which in Britain limits cultivation to the south of England. The cooler and moister summer climate of northern Britain is less suitable for walnut cultivation than southern England because walnuts thrive in regions with warm summers. The major problem with growing walnuts in Britain, and in fact throughout its natural and introduced ranges, is damage by frosts, both in late spring, when young shoots and flowers are very susceptible, and early autumn. The importance of selecting for late leaf-flushing in breeding strategies for walnut cannot be overstated and potentially may be achievable, as flushing is highly heritable.
Given the potential value of producing home-grown walnut timber, and the difficulties associated with its silviculture, it is perhaps surprising that such little research has been conducted on developing better methods of walnut silviculture or on testing improved material for walnut timber production in Britain. Between 1986 and 1987, four experiments were established by the Forestry Commission to assess the growth and survival of two provenances of Juglans regia (Hungarian and English) and six of J. nigra. Four sites were used in the south of England, the most northerly being situated in Northamptonshire. The conclusions were that the site is of greater importance than provenance in terms of survival and height increment, and that on the range of sites used, J. nigra performed better than J. regia. This experiment remains the only attempt to study the potential for growing walnut in Britain using selected material. This research, based on an inadequate range of material, has done little to boost the British forester's confidence in the species. Walnut, particularly J. regia, is seen by the Forestry Commission as a minor species of little economic importance on a national scale, as is evident from its exclusion from current breeding strategies.
Provenance collections of Juglans regia were initiated in the early 1980s in Switzerland and include 20 sources from wild populations in India, Pakistan, Nepal and Bhutan. Several provenances, particularly material collected from Bhutan, were found not to be sufficiently frost-resistant. After nine growing seasons, material from Pakistan and Kashmir was showing good potential with 35 % of genotypes considered of suitable quality for furniture production and 35 % suitable for veneer quality production. A European Commission-funded joint research programme (Proposal PL96-1887 in FAIR III) known as W-Brains focused on the production of high quality wood for furniture, by walnut species (J. regia, J. nigra and their hybrids) involving breeding programmes and the development of new technologies and markets. The goals of this programme are to increase the number and the quality of walnut trees planted in Europe and to standardise the production of walnut timber according to their utilisation. The UK has no formal links with this programme.
Black walnut research is advanced in the U.S.A. where improved stock for forestry is readily available. Much of this research has been co-ordinated by the Walnut Tree Council. In the UK the new Walnut Club has recently been established to co-ordinate research and promote walnut species for both timber and fruit growing .
Walnut Research at the Northmoor Trust
The Northmoor Trust is actively promoting walnut research through its own projects and through the collaborative partnership under the British and Irish Hardwoods Improvement Programme (BIHIP). Walnut research at the Trust has concentrated on the common walnut but more recently has expanded to include the black walnut. The walnut trials include one of the largest collections of walnut (Juglans regia) genotypes found worldwide, incorporated in a tree improvement programme and various silvicultural trials. The trials are based at our research centre Paradise Wood and at other sites in southern Britain.
COMMON WALNUT (Juglans regia) ESTABLISHMENT TRIAL
A trial testing some methods for the successful establishment of walnut, particularly the use of treeshelters and a stumping treatment.
COMMON WALNUT (Juglans regia) COMBINED PROVENANCE/PROGENY TRIAL
A large multi-site trial evaluating the suitability of the genotypes collected from 18 countries for timber production in Britain. Genetic variation studies are also being undertaken. This long-term trial (at least 50 years) will also yield much-needed silvicultural information on the species.
COMMON WALNUT (Juglans regia) SILVICULTURE TRIAL
A trial testing the effects of growing walnut in combination with various tree and shrub nurse species. In addition to assessments of height and stem growth, evaluation of tree architecture will be undertaken regularly.
COMMON WALNUT (Juglans regia) DIRECT SEEDING TRIAL
A trial testing methods of establishing walnut plantation by direct seeding, planted in 2001. First results will be posted in late 2002.
COMBINED WALNUT (Juglans regia & J. nigra) NITROGEN TRIAL
Testing the effects of applying artificial nitrogen to newly planted walnut trees, planted in 2001. First results will be posted in late 2002.
BLACK WALNUT (Juglans nigra) PROGENY TRIAL
A new series of trials being prepared at present, proposed planting date is in autumn 2002. This is a joint collaborative project with The National Forest and Jaguar Cars. Further details will be posted soon.
