Botanic Gardens’ trees among the best in the world

Press, 10 January 1987, Page 18

Botanic Gardens’ trees among the best in the world

By

DERRICK ROONEY

This week the country diary comes to town, for a look at the trees of the Christchurch Botanic Gardens — a splendid ornamental park and arboretum with a history of planting stretching back to 1863. Occupying an area of about 26 hectares within Hagley Park, bounded by Rolleston Avenue and a curve of the Avon River, the garden has a naturally light, sandy soil in which plants of many species have thrived. Over the years, successive curators have built up a remarkable collection of trees, shrubs, and smaller plants from many parts of the world. Many of the trees have grown into noble specimens, among the best of their kind to be found anywhere in the world, and despite losses through storms, natural attrition, and remaking of parts of the garden these trees remain, both as the framework for a garden of singular beauty and as a valuable reference collection of living material. There is no space, here, to describe all these trees; the purpose is to mention, briefly, some that I found particularly impressive on a circular tour, starting at the kiosk. Other visitors will note other specimens which seem just as good, or as Interesting. The measurements cited, unless otherwise noted, refer to the diameter of the trunk at breast height (1.4 metres), and were taken a few weeks ago with the help of the Botanic Gardens foreman, Kevin Garnett. Unfortunately, for technical reasons, we were unable to assemble accurate up-to-date height measurements, but most of the trees have been measured at various times in the last 20 years, and the most recent is listed where possible. "A notable tree on the riverbank east of the kiosk is the Dutch elm (Ulmus X hollandica), a hybrid between the smooth-leaved elm and the wych elm which arose in Europe, perhaps in the seventeenth century. Once favoured as a timber tree, this elm has all but disappeared from Britain and Europe as a consequence of Dutch elm disease. New Zealand is fortunate to be one of the few countries free from the disease and this specimen has thus-re-tained its health and vigour. We measured its diameter at 137.5 cm.

Not far away, on the edge of the pond, is the giant radiata pine, one of the biggest trees in the Christchurch region. The age of this pine is not recorded, but it could be 119 years old; it is known that radiata seedlings were raised in a Christchurch nursery about 1868. It remains healthy and vigorous, and like many trees in the garden is still packing on volume at a good rate: from 174 cm in 1963 its diameter had increased to 198 cm in 1970 and 221 cm in 1986 — making it arguably a better log of wood than the one that Auckland took away. Near the Paulownia lawn is another good conifer, a shapely Ponderosa pine, smaller than some that may be seen inland in early homestead gardens but listed by the Forest Service in 1970 as the biggest of its species in the Christchurch area. Its height was measured at 90ft in 1970 and its diameter at 101 cm; it now measures 117 cm d.b.h. The best Ponderosas in North Canterbury, incidentally, are probably those at Cheviot Hills Park, and Homebush Station, Darfield — the emergent top of the Homebush tree can be seen from State highway 72, in a mixed woodlot on the slope behind the woolshed. A noble tree near the West bridge in the Botanic Gardens is the big ash (Fraxinus excelsior). Despite storm damage to its top this is probably the biggest, and best, common ash in the country. Its height in 1981 was measured at 36 metres, and its diameter now is 120 cm (104 cm in 1970). A tree recorded near Masterton has a more massive trunk but is not nearly as tall. Monterey cypress (Cupressus macrocarpa) is a familiar tree in New Zealand and there are many large specimens but only a few are more massive than those in the Botanic Gardens. Separating the bog garden from the native section is a multistemmed example with a huge, fluted bole around which a seat has been built.? Its girth, measured just about the seat, is now Bm, having increased by 60cm since 1971. Among the interesting trees bordering the River Walk is the

so-called “New Zealand blue gum,” a spontaneous hybrid between the familiar Tasmanian blue gum (Eucalyptus globulus) and Eucalyptus umigera. This tree, now showing signs of advanced age, is believed to be the sole survivor of the original cross. Of unknown age, it was measured in 1981 at 30m in height. Burstall and Sale (“Great Trees of New Zealand,” 1984) recorded its diameter as 132 cm, but we made it rather smaller, at 127 cm. That still makes it a big tree! An uncommon tree of which the garden has an exceptionally good specimen is the upright or “cypress oak,” Quercus robur var. fastigiata. This unusual form of the common oak was first discovered in a forest in Germany in the seventeenth century, and propagated by grafting. It remains narrowly columnar instead of developing the broad, spreading crown characteristic of the oak. In New Zealand it is quite rare and this was the only large specimen recorded in Forest Service surveys in 1970 and 1981.

It is growing strongly, having increased its diameter from 71cm in 1970 to 102 cm, and its height to about 16 metres. By way of comparison, the biggest British specimen listed by the Forestry Commission was measured at 23m x 112 cm, at Hardwick Park. As for the common oak, there are numerous fine specimens, perhaps none finer than the “Albert Edward oak,” the patriarch of the garden. Planted in 1863 to commemorate the wedding of Prince Albert (much later, King Edward VII) and Princess Alexandra, it was the first tree planted in the gardens and looks set to outlive most of the others. Since 1970 its diameter has increased from 124 cm to 138 cm. The centennial history of the garden, published by the City Council in 1963, gave its height as 110 ft (33.5 m probably

a mistake. In 1971 the Forest Service measured its height at 23.8 m. From the many fine conifers it is difficult to select “Bests,” but an especially noteworthy and, in New Zealand, rare tree is the Japanese fir (Abies firma), which is probably the best specimen of this species in the country. In Britain this tree is seen much more often, and there are many specimens in the south and west pf that country, but it is interesting that none of the British specimens listed by the Forestry Commission is as big as this Christchurch one, which has a diameter of 136 cm (116 cm in 1970, when its height was 29m). Abies firma is a dominant tree in

the forests in a large part of southern Japan but is of little economic importance. Also notable is the big West Felton yew (Taxus baccata Dovastonii), a form noted for its horizontal branches, drooping at the tips, which create a broad, dense canopy. A whole busload of people could shelter under this tree, whose branch spread was measured at 15.85 m in 1963. We made it 16m in 1986 but the Forest Service measured it at 18.2 m in 1970. This form of the yew is rare in New Zealand, but its history goes back to about 1777, when a Mr John Dovaston, of West Felton, near Shrewsbury, paid a local cobbler 6d for a young yew tree to plant near his well to prevent

erosion. Subsequently the tree developed its distinctive branching habit. The original tree was still growing at West Felton in 1974 and presumably is still there in 1987. As noble trees go, the big blue atlas cedar opposite the herbaceous border is a star of the gardens. This tree, 140 cm in diameter, has a massive, clear trunk to 6m, with virtually no taper. Also in this group of big old trees are a very large Holm oak (Quercus ilex), not as big as the one in the Queen Mary Hospital grounds, Hanmer Springs, but of better form. Nearby are two other evergreen oaks that are rare in New Zealand: the Mediterranean cork oak (Q. suber) and Q- incana, from North America. For some reason the Forest Service did not measure Q. incana but it is a notable specimen of an uncommon tree, somewhat drawn up by its neighbours but possessed of a stout trunk measuring 92cm. Many kilograms of acorns from this tree have been distributed to other botanic gardens and institutions. Elsewhere in the Christchurch region the only mature cork oaks accessible to the public are those near the entrance to Bradley Park, at Charteris Bay, but these are poor specimens compared with the Botanic Gardens tree, which has a massive, spreading crown. It is still growing strongly, having increased its diameter from 89cm in 1970 to 107 cm.

Much the biggest tree in the garden — and in Christchurch — is the giant Australian alpine ash (Eucalyptus delegatensis) in a

group of eucalypts between the rose garden and the rock gardens. This is one of Australia’s forest giants, recorded there as growing to heights of more than 60 metres and diameters of 2m or more. This Christchurch specimen, 38m tall in 1982, has a lot of height to catch up, but already has the bulk, and. is growing rapidly. From 203 cm in 1963, its diameter has increased to 236 cm in 1970, 279 cm in 1981, and 297 cm now. Noted also for its bulk in comparison with specimens in their natural habitat is the giant Californian madrona tree (Arbutus menziesii), the biggest specimen of this usually small tree in New Zealand, and posibly one of the biggest anywhere. Extensive tree surgery and branch bracing in recent years have helped to maintain the health of this highly prized tree, which is more than 24 metres tall and now has a trunk diameter of 204 cm at 30cm, compared with 183 cm in 1970. The Madrona is related to the Mediterranean "strawberry tree” (Arbutus unedo) of which the garden also has good specimens. There are too many other fine trees in the Botanic Gardens to name here. Some are good examples of much-planted species, some are uncommon, and a few are not to be seen elsewhere in New Zealand. A small-leaved lime (Tilia cordata), which we measured at 110 cm diameter, is the largest of this species recorded in New Zealand; it is not common. Since 1970 its diameter has been increasing by Icm annually. The rare Californian laurel

(Umbellularia califomica), planted about 1870, should be in , its dotage but is still growing ; vigorously, having increased its ' diameter to 127 cm from 99cm in 1970. ; This is a remarkable speci- ■■ men;; in 1981 its height was measured at 28m, which is probably at least as tall as, and perhaps taller than, any specimen in its native California, where it is a small tree, often just a shrub. Umbellularia is related to the sassafras of the south-eastern United States and the bay laurel of the Mediterranean, and like them it has aromatic foliage — rather more aromatic than the others, in fact, for the leaves contain highly volatile substances which are released when the leaf is crushed and if inhaled can cause a brief, choking sensation followed by a piercing, fortunately temporary, headache; most unpleasant Be warned! A field maple (Acer campestre), which is more than 16 metres tall, is the largest of its species in New Zealand, despite its being partly suppressed by a nearby, large lime tree. Its diameter now is 97cm, compared with 91cm in 1970. Among the very rare items is a “Kentucky coffee tree,” Gymocladus dioicus. This has suffered considerable damage in recent years and as a result has undergone extensive surgery, but it is still packing on diameter. We measured its trunk at 73cm, compared with 58cm in 1970. This unusual tree belongs to the pea family, and there are few if any other specimens in New Zealand.

The patriarch of the garden