Botanic Gardens key role in conservation of rare plants

Press, 19 December 1981, Page 17

Botanic Gardens key role in conservation of rare plants

By

DERRICK ROONEY

The Christchurch Botanic Gardens, as Christchurch people are fond of repeating, are famous round the world for the standard of their planning, planting, and maintenance: as a horticultural institution they are second to none in New Zealand; and as a botanic garden they have been rated by respected overseas authorities among the world's top dozen. These points are well known.

Less well known is the role played by the botanic gardens as a custodian of rare or endangered plants, and in recent talks to Christchurch horticultural organisations the curator (Mr Alan Jolliffe) has been emphasising this aspect of the gardens. He believes that although horticulture will always take first place, conservation will play an increasingly important role in the activities of the botanic gardens, which maintain probably the largest collection of temperatezone plants in New Zealand, perhaps in the Southern Hemisphere. These have been gathered together over upwards of 120 years, since the first plantings were made on the botanic gardens site in 1863. Recently, as a result of the co-operation and generosity of botanists in the Botany Division of the D.S.I.R. at Lincoln, new native plants have been added to the collection.

There has never been any conscious policy at the gardens to compile an exclusive collection of rare plants, but successive curators, and some members of the staff,

have been intensely interested in collecting, cultivating. and hybridising New Zealand plants, and as a result a comprehensive “source collection" has been built up. These plants provide propagation material, mostly seeds, for exchange with overseas botanic gardens and institutions. Plants and seeds come in from many private collectors, too. and in this way many rare exotic as

well as native plants are acquired. Numerous plants of which the Botanic Gardens hold specimens or propagation material are listed in the “Red Data Book.” through which tabs are kept internationally on the world’s rare species. This list is maintained and regularly revised under a scheme run by the threatened plants committee of the international conservation organisation, 1.U.C.N., and administered by the keeper of the herbarium at the Royal Botanic Gardens, Kew. As well, New Zealand now has its own “red data book" of rare and endangered plants and animals, issued by the Nature Conservation Council. Species listed in the book are classified in four categories: Endangered — these are species in danger of extinction. Vulnerable — species in no immediate danger, but vul-

nerable to the risk of extinction through small changes in their habitat, or interference with it. Rare — Plants which are not in danger of extinction, but

which exist in small, localised populations. Extinct — no longer known to exist in the wild. Some 40 to 50 plants in the New Zealand collection at the Botanic Gardens come in one or another of these categories. Ironically, some of them are widely known and grown in horticulture, for example the Chatham Island forget-me-not, the kaka beak flower (clianthus), and Hebe armstrongii. from Castle Hill. The forget-me-not has been browsed almost to extinction and the wild population of kaka beaks, in the northern North Island, was never very big and is now down to a few hundred.

The hebe, though surviving in even smaller numbers, has a more secure future and is one of the success stories of recent conservation efforts in New Zealand. For many years believed to be extinct, it was found by a D.S.I.R. scientist doing research in the 1970 s in the Bog Pine Reserve at Castle Hill. Initially, only one plant was recorded, but a later search revealed several more. Seed was taken back to the Botany Division, and in due course seedlings raised there were reintroduced to the wild.

By 1978 the number of specimens of Hebe armstrongii growing at Castle Hill had increased to 47.

Though the Botanic Gardens is holding plants raised from the Castle Hill seed for reference purposes, it had no direct hand in this instance

in the reintroduction of the plant to its wild habitat. It is playing a direct role, however. in the case of Aciphylla inermis, a species of wild Spaniard from Mt Cook. A group of plants of this species is being grown on at the gardens in the hope that they will yield seed from which plants can be raised for reintroduction to Mt Cook National Park, where. Mr Jolliffe says, it is believed to be extinct. Unfortunately, all the plants that have flowered so far have been females, and there has been no male flower to pollinate them, so as yet no seed has been obtained. Some have yet to flower, and Mr Jolliffe is hopeful there will be a male among them. The species could be propagated by division and reintroduced to its habitat in

that way. but this would not be a satisfactory solution because any wild species incapable of seminal reproduction is doomed.

What are the aims of the Botanic Gardens in such dealings with the country s rare plants? According to Mr Jolliffe, they are four-fold; to grow them, to get to. understand their requirements and cultivation, to propagate them, and to disseminate them to other institutions or, in the case of plants with horticultural merit, to the nursery trade. Some botanical curators are tight-fisted with their rare plants but Mr Jolliffe believes in spreading them

about, when he can. If a

plant is grown in a number

of different gardens the chances of its being lost are much lower, he says, than if it is held in a single botanical garden. The gardens have already played a hand in a classic case of rediscovery which strengthens this attitude towards rare plants. This was the case of the Easter Island kowhai. Sophora toromiro — the only tree known to grow on the island in historic times. In the 1960 s this tree was extinct in its habitat, and it was only through a response by the Christchurch Botanic Gardens to a world-wide request for seeds or seedlings that the tree was re-estab-lished on Easter Island. Sophora toromiro is a small, rugged tree, fairly closely related to the New Zealand kowhais and not dissimilar to them, except that it has smaller flowers.

Even when the earliest European explorers visited Easter Island in the eighteenth century it was rare, existing only in scattered

groves, and after 1871, when sheep-breeding was initiated on the island, the decline of the toromiro was hastened. A Scandinavian botanist who visited the island in 1917 found only one live specimen, from which he collected seeds which later germinated at the Gothenburg Botanic Gardens, but never flowered and eventually died. Thor Heyerdahl found a few specimens during his 1955-56 expedition to the island, but when the superintendent of the agricultural

station on the island made a search in the early 19605. none could be found.

He got in touch with the Danish consul in Santiago, who then initiated, through the Danish Dendrological Association, a search of the world's botanical gardens and arboreta for the toromiro. The only affirmative response came from Christchurch.

Mr H. G. Gilpin, then director of parks and reserves for the City Council, recalled that a specimen was growing in Victoria Park. He harvested seeds from it and sent them to the Danish organisation, which sent them on to Easter Island. The tree was then, and probably still is, the rarest of the' rare plants in the Botanic Gardens collection. It also has the distinction of being the only known specimen to have set viable seed in cultivation; others raised in Europe proved to be sterile.

But the tree is now approaching its half-century, and its likely life span is not known. Il was planted in the early or mid-1980s, having been raised, it is believed, by the late Jack Humm of Nairns Nurseries. Addington, from seeds collected by the late Professor MacMillan Brown when he. visited Easter Island about 1934. Some seedlings apparently were planted also in the professor's own garden, but the fate .of these and any other seedlings raised at Nairns is not known. The firm closed many years ago. and most of its former gardens in Lincoln road are now covered by the earthworks and approach for the Southern Motorway overbridge. The story of the Toromiro is possibly the best illustration of the role that botanic gardens can play as “conservators of nature," Mr Jolliffe says.

It is a role in which the Christchurch gardens are somewhat restricted, because unlike the famous overseas botanical gardens, which have access to government funds for their research projects and expeditions, the Christchurch gardens are funded solely by a local authority, the Christchurch City Council. But it is not always necessary to mount expeditions to remote regions of the world to bring rare plants into cultivation.

One shrub growing in the Cockayne Memorial Garden—the section devoted to native plants—came from much doser to hand. This is Carmichaelia kirkii, a smallflowered broom which grows into a low, semi-trailing shrub. - It is unlikely to win any prize for showiness, but Mr Jolliffe believes it is

important to maintain it in the collection. Why? Because it is a rare native of Christchurch.

Other Canterbury plants held in the gardens but nowrare in the wild include the “fierce lancewood” (Pseudopanax ferox). This is well known in cultivation, but in the wild, Mr Jolliffe says, is now confined to relatively few stations, one of them being the Rakaia Gorge. The specimen in the gardens produces viable seed, and seedlings come up all round it. From Marlborough, there are several fine specimens of the tree-sized native brooms, and Mr Jolliffe believes it is important to preserve and propagate these, though this is proving difficult because of insect attacks on the ripening seeds. These interesting plants are very vulnerable to maninduced changes in their habitat in the upper river valleys of Marlborough, and they are being decimated by weed spraying; brush-killing chemicals are incapable of differentiating between the

native species and the unwanted exotic broom, gorse, and briar. From elsewhere in New’ Zealand the gardens have many plants—such as a tiny, as-yet-unnamed corokia species from North Cape; an unusual olearia (tree daisy) from Opotiki; the Chatham Islands geranium, now almost eaten out of its habitat by livestock; coxellas from the Chathams; and the rare Great Barrier Island cabbage tree. Cordyline kaspar.

From Stewart Island comes the tiny, prostrate Gunnera hamiltonii — a miniature cousin of the giant Chilean gunneras that grow on the margins of several ponds in the gardens. Gunnera hamiltonii is in a very real sense an endangered plant, says Mr Jolliffe. It can be increased only by vegetative means because nd female plants are known in the wild, therefore there cannot be any seed. Among the rare and endangered exotic plants in,,the collection are two that may startle New Zealanders: the

macrocarpa and the radiata pine.

Both species are propagated and distributed commercially by the million, but as true wild plants they are today all but unknown. Both have restricted and localised distribution on the Monterey Peninsula, California, and the macrocarpa is the more rare of the two—the main groves are found in an area only five kilometres long. Thus both are listed as endangered. even though they are cultivated —and naturalised—in many countries. Very large specimens of both are growing in the Botanic Gardens.

Other trees, familiar in cultivation but rare as wild specimens, include the Madrona tree (Arbutus menziesii, of which Christchurch has what is believed to be the world’s biggest specimen). the gingko, the dawn redwood (metasequioa). the “Arctic birch” (Betula nana). and the zelkovas, rare relatives of the elm from Japan, China, and south-east-

ern Europe. All are growing in the botanic gardens. Under glass, too, rare exotic plants are grown. There are cycads, which are living remnants of prehistoric vegetation; rare succulents, bromeliads, and insectivorous plants; and the fabulous Draceana draco, the “dragon tree” of the Canary Islands. The alpine collection includes numerous rare small plants and bulbs, too, but many of these, like the succulents, have to be grown under lock and key. Gardeners. despite their reputation for down-to-earth honesty, include many lightfingered people who invariably have an eye for the rare and choice.

Elaborate security grilles have had to be installed in the Foweraker House, where alpines are grown, and the Garrick House, where the succulents are displayed. It was even found necessary to screen off the under-stage ventilators in the Foweraker House because people were getting plants out through them. " •