Westonbirt Arboretum John White

Establishing an arboretum is necessarily a long-term project but that at Westonbirt is now fully mature, having been founded in 1829 and systematically extended and planted over the years. Originally developed by private landowners it has since 1956 been the responsibility of the Forestry Commission and now covers some 240 hectares, on which grow 15 000 trees and shrubs. It is both an important scientific collection and research centre and a valuable public amenity, for education and recreation, attracting 200 000 visitors a year.

Westonbirt Arboretum is a remarkable collection of over 1.5 000 listed woody plants dating from the present day back to Edwardian and Victorian times. It is now maintained, by the Forestry Com- mission, primarily as a scientific collec- tion of trees, although shrubs play a major role. The great variety of plants, the great age of some of them, and the landscaping of this collection make it a very attractive place for recreation and a most valuable amenity feature. Full advantage is taken of the educational potential of such an asset. The Forestry Commission is advised at Westonbirt by a consultative committee which includes members eminent in fields related to arboretum management, landscape de- sign, and forest research.

The location It is likely that the location for Weston- birt Arboretum was originally chosen by the founder, Robert Stayner Holford, because, in a predominantly limestone district of central England with shallow, rather heavy soils, it contains areas of deeper sandy loam sufficiently lime-free to grow coniferous trees and Rho- dodendrons. It is said that Holford disco- vered these isolated sandy areas on his Cotswold estate prior to 1829 by observ- ing the digging patterns of rabbits, and badgers. The sporadic geological sandy deposit, derived from Hinton Sand, occurs in small patches, seldom exceed- ing six hectares in area or two metres in depth, all along the Cotswold Hills be- tween Bath and Cirencester. Less than

John White

After training in forestry at Bemore, West Scot- land, joined the Research and Development Division of the Forestry Commission in 1962. After working in a range of out-stations in the UK he was appointed Curator/Botanist at Wes- tonbirt Arboretum in 1975. Since 1987 he has been Forestry Commission Dendrologist.

Endeavour, New Series, Volume 12, No. 2, 1988. 016~9327/W $3.00 + .OO. 0 1988. Pergamon Press pk. Printed in Great Britain.

10 per cent of the 239-hectare arboreturn is on this very desirable soil. The remain- der is on shallow brown earth over oolitic limestone of the Jurassic Acton Turville Beds. Quite impossible for any- thing but moles to dig in, but favoured by lime-loving trees.

Westonbirt is on nearly level ground, but for a dry valley through the centre. It lies on a virtually unbroken ridge of land that runs through the heart of England between Bath and Grantham. The elevation of the arboretum is about 120 metres above mean sea level. There are no topographic features such as high ground, open water, or outstanding dis- tant views to enhance the landscape, so design has always depended entirely upon careful placing of plants in relation to each other and to open glades, grass rides, and pathways. A Holford tradi- tion of planting developed which is largely perpetuated today. Two of its most fundamental guidelines for land- scaping with trees are never to plant more than three subjects in a straight line (except in a forma1 avenue) and never underestimate the importance of large open spaces.

The climate is broadly similar to the rest of central England softened perhaps by the proximity of the Bristol Channel to the west. Snow seldom lies for long, but winter temperatures can be low. Severe winter winds by their force or the wind chill factor would damage much of the collection were it not for the artificial shelter-belts of hardy trees planted along the boundaries. Gales at any time of year do occasionally cause considerable dam- age, particularly to the larger trees which may be broken, or, when the ground is very wet and soft, blown down. Late spring frosts are infrequent but Camellia and Magnolia flowers may be spoiled by them from time to time. Rainfall has been recorded each day since 1880: the average annual figure is about 890 mm (35 inches), most of which falls between August and January.

History The arboretum was founded by Robert Holford in 1829. Many of the back-

ground and shelter trees he planted still stand today. These consist mainly of English oak (Quercus robur), Scats pine (Pinus sylvestris), Sweet chestnut (Cas- tanea sativa), Beech (Fagus sylvatica), and European larch (Larix decidua). He defined the shape of his new woodland in this way on what had until then been open meadow. The budding arboretum was considerably expanded to the east in 1855, by which time it was in clear view of the shortly to be re-built Weston Birt (now Westonbirt) House. Three straight vistas were designed to dissect the arboretum, two to lay open rather blank views beyond the far northern side, and one to end in the trees. One of these is aligned on to St Catherines church which adjoins the site of the previous house. The other two are in direct line with the present building, which is interesting as they pre-date it by several years. In the 1855 development considerable use was made of hardy evergreens such as Yew (Taxus baccata) and Holm oak (Quercus ibex). These still contribute greatly to the shelter of tender species. Holford shared the general enthusiasm of the landed gentry of the time for the north-western American conifers which were being introduced by David Douglas, William Lobb, Hartweg, and Jeffrey in the 1850s. Probably the first of these trees planted at Westonbirt included Douglas fir, (Pseudotsuga menziesii), Redwoods (Se- quoia sempervirens and Sequoiadendron giganteum) , and Incense cedar (Calocedrus decurrens). Holford con- tinued planting until he died in 1892, a span of 63 years during which he ac- quired and planted almost every species of tree introduced to Europe by that time.

Sir George Holford, Robert’s son, joined the work from about 1875 and was probably responsible for the planting along the Willesley, Waste, and Broad Drives in Silk Wood. This was started in 1876 in a wood which had been oak standards and hazel (Corylus avellana) coppice since before 1292. Features such as the still famous Acer glade and colour circle were also established. Sir George would invite quests, particularly from

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Figure 1 The arboretum is designed to be attractive in all seasons. These contrasting pictures show the Acer glade in full colour and a view of a ride in mid-winter.

London, to annual ‘colour parties’ where he would show off his tree trea- sures with many sumptuous trappings. He could also have shown off other treasures, for he was a noted collector of books, pictures, and other works of art, housed partly at Westonbirt.and partly at his London home, Dorchester House. After his death in 1926 his collection realised over f400 000 when auctioned at Christie’s, He added hundreds of plants to the collection, including several new introductions resulting from the many botanical explorations of the Americas and Far East that set out between 1890 and 1920. He was a!so an enthusiastic collector and breeder of Rhododendrons; many of his actual plants survive still although some were, and still are, nameless. In 1927 A. B. Jackson, the notable Kew botanist, com- piled the first Westonbirt catalogue almost 100 years after the earliest plant- ing. On the death of Sir George, sadly just before the magnificent catalogue was published, the fourth Earl of Morley succeeded to the estate. Although Lord Morley did not live in Westonbirt House, his enthusiasm for the arboretum was in no way less than that of his late uncle. With the continuing ben- efit of Sir George’s curator W. J. Mitch- ell living on the site, planting proceeded on a vast scale. When Lord Morley died in 1951 Westonbirt Arboretum had accomplished 122 years of sustained planting by just three owners. The arboretum then suffered some years of decline until 1956 when many of the less robust and younger specimens were lost. This should have been the time when replacements for many of the ageing big trees in the collection were planted. They were not, the age class distribution now has suffered because of it.

The Forestry Commission In 1956 the Forestry Commission took over Westonbirt and placed it in the care of their research department. First task was to repair the effects of shortage of la- bour and neglect during the preceding years. This consisted partly in rehabilita- tion of the structure of the arboretum, by the removal of dead trees and salvage of rare specimens that had been engulfed, and partly in clearance of overgrown thickets and shelterbelts. New replace- ment shelter trees were planted. Clear- ings were opened up for new specimens and improving vistas. Mapping speci- mens, cataloguing and labelling, and improving the grass sward was initiated. Clean gravel paths were laid down or resurfaced and car parking facilities were introduced. A major difficulty was that in order to establish large numbers

Figure 2 Storm damage can be mitigated by planting shelter belts nevertheless a constant hazard.

but is

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Figure 3 As an aboretum of international status, Westonbirt ’ regularly receives material from all parts of the world.

of big trees such as oak, beech, Scats pine, and Douglas fir it was necessary to make considerable clearings. It was, and still is, important never to allow these operations to appear wholesale nor det- rimental to the enjoyment of the peace- ful arboreal setting, or make them exten- sive enough to let damaging winds into the canopy. Although Westonbirt has been nearly as comprehensive as to temperate species as a single arboretum could be in the past, this is no longer the main aim. With improved communica- tions between and within botanic gar- dens and arboretums, individual cura- tors are able to specialize in what they

Figure 4 Although trees are long-lived many die each year of old age or fall victim to the destructive honey fungus (Armillarieh melea). In an average year losses from these causes may amount to 200-300 trees. Loss from honey fungus can be mitigated by regular inspections (left).

can grow and manage best, in full know- ledge of what everyone else is doing. From 1979 specialist collections were begun at Westonbirt. These include genera such as Prunus, Quercus, Sorbw, Fraxinus, and Tdia. In 1984 national collections of lowland willow (Salk) and Japanese maples (Acer japonicum and A. palmatum) were started. These form part of a huge nationwide series of collections of cultivated plants adminis- tered by the National Council for the Conservation of Plants and Gardens. (N.C.C.P.G. c/o Wisley Garden, Sur- rey, England.)

Present objectives The Forestry Commission has three objectives at Westonbirt; these, like the legs of a tripod, are each of equal importance and interdependent one upon the other. Broadly they are the maintenance of the collection; inter- pretation in its many forms; and recrea- tion. The collection is maintained to perpetuate what is standing on the ground, a huge gene pool of ancient and modern woody plant material, which is extended as appropriate. Additions,

Figure 5 The herbarium is an important recent addition to the arboretum.

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these days, are strictly limited to authen- tic material; that is, either a wild col- lected species or a genuine, verified horticultural subject. The needs of silvi- culture and arboriculture are met by experimentation, demonstrations, and research. Contributions to the science of forest botany are made through special studies of phenology, morphology, tax- onomy, and nomenclature. A recently established herbarium supports these investigations. Few sites provide such a favourable opportunity to examine so many live specimens in one place.

Formal interpretation of the collec- tion is largely accomplished through the arboretum’s own eduction department where a wide range of intellectual levels are catered for. Less formal interpreta- tion is disseminated by all staff the whole time, so much so that it is difficult at times for the visitor to separate inter- pretation from recreation. Everyone en- tering the arboretum, casual or profes- sional, is regarded as a target for some level of ‘education’. Each publication, display item, or specially featured trail is aimed at a pre-determined audience.

It is intended, by explanation, to en- lighten every visitor but at the same time not make this too obvious. Most people appear to enjoy learning about trees, so clearly this is an example of successful integration between recreation and education.

Recreation, the final objective, is achieved by the collection being open to the public throughout the year. All de- velopments and methods of manage- ment are designed to be as aesthetically pleasing as possible. Enquiries are sym- pathetically and efficiently answered; from a simple direction to a complicated scientific query. The provision of fairly smooth public paths and a certain amount of mown grass add considerably to the recreational value of the site.

The Arboretum today The arboretum today is a thriving heal- thy collection of trees and shrubs to which are added about 500 new plants every year. Losses in a year vary accord- ing to the arbitrary occurrence of storms. Old age and honey fungus (Armillariella mellea) in an average year may account for some 200-300 trees. Comprehensive study collections are the priority now, although representatives of as many genrea as possible are still included. A whole genus reference collection gives the dendrologist the essential ingre- dients to increase his understanding of taxonomic problems and plant rela- tionships within a group. In the most complex genera each seed generation is slightly changed from its parents and intermediate forms eventually make established classification and keys un- workable. Constant revisions and im- provements in nomenclature are possi-

239.42ha. 48.30ha.

146.20ha. 44.92ha. 84.54ha.

Total area of Westonbirt Arboretum

Original arboretum Silk Wood Service areas &grazing land Planted Arboretum (1987) Unplanted, available

to plant (1987) Ancient semi-natural

woodland Grazing (leased) Paths, roads and

hardstandings

15.68ha.

47.65ha. 20.20ha.

6.89ha.

About 200 000 people visit the arboretum each year and this demands the provision of appropriate facilities in the form of parking for coaches and cars and refreshment accommodation. Compaction damage by so many people walking in a confined space has been largely overcome by the carefully plan- ned provision of gravel paths. Motoring is not permitted except to and from the car park which is close to the visitors centre. Short level circular routes are marked out for the disabled and elderly. The visitors centre was opened in 1978.

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ble only if live collections are available. Westonbirt is managed now very much as an essential component of all the other tree collections in the British Isles, and in some respects the world. It has always been a great collection but until recently one that always had an air of mystery about it. Only in recent years has it been properly recorded and sur- veyed. One of the first computer inven- tory systems for trees was evolved at Westonbirt. This does much more than simply list the collection. The arboretum catalogue, and its’ companion atlas, is a vital management tool; a database into which numerous items of information are fed. Each specimen, in addition to having the usual botanical data, has information regarding condition and health leading to envisaged programmes of work. All management data are sorted automatically into priority order which contributes greatly to public safe- ty. From the arboretum atlas it is possi- ble to give a complete update of land use. For example, in 1987 the following ground treatments were assessed:-

Mown Grass - maintained down to ab- out 8cm Meadow grass - cut only once or twice a year Grazing Paths - including roads and hardstand- ings Estate - buildings, private gardens etc. No ground treatment - e.g. under wild wood.

These categories were further split to give a picture of present use and poten- tial for further expansion. From this analysis the following areas have been quantitifed:-

It consists of an interpretative pavilion in which publications and information can be obtained. There is an exhibition de- picting some of the features of the arboretum; this is changed, in part, each year. A scale model of the estate forms a vital part of the exhibition for the benefit of those who find maps difficult to inter- pret. The central building has been care- fully sited to blend into the surrounding woodland, and reflects the spirit of the arboretum by its use of many timbers from all over the world. The supporting framework is of home-grown Douglas fir. This stands on a hardwood floor made from Angelique (Dicorynia guianensis). The ceiling is of Baltic pine with North American red cedar (Thuja plicata) shingles over it. The beam over the open fireplace was cut from a Silk Wood oak and the information desk was made from an arboretum-grown Califor- nian nutmeg tree (Tmreya californica). These exotic timbers, reflecting the exo- tic trees outside, relate to the site through walls of local limestone which rise up from the ground away from the building and project themselves through the walls to form a central core of crafted stonework.

The future Westonbirt Arboretum is so valuable that its future is likely to be assured for all time, but even more projects are in the pipline for further improvement. Accessibility to the public, itself a poten- tial threat to the well-being of the trees and environment, is likely to be further improved so that visitors can see more. Most visitors come for a pleasant day out, but at the same time specialists or those simply seeking peace and quiet are not forgotten. A long standing problem, lack of labels on the trees, has been a cause for criticism, and this is being put right. A proportion of label engraving is now being put out to specialist contrac- tors and production will increase.

A growth area at the arboretum is education; in 1987 numbers of children participating in educational programmes rose by 20 per cent over the previous year. Full-day programmes are arranged during off-peak times: whole days are set aside for a single school class. The education unit has provided information for the National Education Resources Information Service (N.E.R.I.S.) data- base, which is accessed by some 6000 teachers a month. This together with direct mailing and repeat visits ensures a steady stream of bookings. In future provision for adult education, in-service training, and teachers workshops will be expanded. It is likely that day schools could also be organised independently, perhaps in conjunction with a County Naturalist Trust or university. In Bri- tain, an ever increasing number of ordin- ary members of the public seek a level of

tree instruction that can be met only by the existence of great tree collections. These are the raw material for books and illustrations, particularly now that so much wild habitat has become so fragile or been lost. Westonbirt stands as a living textbook of authentic reference material. There is nothing static about it either, as seasons come and go the plants change. Each can be observed during that, frequently short, period in the year when it is most distinctive. This is the advantage of a live collection has over the static printed word or picture.

The conservation aspects of Weston- birt are very varied. Ex-situ conservation of vulnerable species is one that springs more easily to mind and is probably the most significant. The prospect of re- introducing a previously lost species to the wild is stimulating, but the theory of

re-introduction frequently does not stand up in practice. Tree life can be measured in hundreds of years, over which time the future pressures and threats it will sustain cannot be forecast. There is perhaps a case for permanent ex-situ safety-net collections. Massive introductions of unauthentic or in- appropriate material into wild environ- ments can also be catastrophic. Ex-situ holding time needs to be lengthy so that the full consequences of release to the wild can be researched. In addition to wild plant conservation there is a need to protect cultivated plants. Westonbirt, in close co-operation with the N.C.C.P.G. plays a vital role in this. Rare breeds of cultivated trees and shrubs can easily slip unseen into extinction.

The future for Westonbirt is going to be as exciting as the past has been.

Contacts throughout the world continue to provide new and replacement plant material and seeds. Collectors continue to discover new trees, even as close to home as within the British Isles. In 1987 a previously unrecorded Sorbus was dis- covered in central Ireland. Genetic re- search produces new improved trees. The arboretum not only grows these new artificial plants but it contributes basic raw material for future research pro- jects. In a single day, for example, improved hybrid larch (Larix x eurolepis) may be planted while Cauca- sian wing-nut (Pterocarya ,fraxin~folia) cuttings are sent away for a further programme of testing. Westonbirt is constantly providing opportunities for everyone whatever their level of in- terest, to become more familiar with trees.

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