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The Cultivation and Repatriation of Alsinidendron trinerve, a Threatened Hawai'ian Endemic

Volume 2 Number 5 - August 1995
Mike Maunder, David Orr, Martin Staniforth and Belinda Parry

Many large botanical institutions of northern countries hold diverse collections of plants. The conservation utility of those collections is partly compromised by a lack of data that can guide decision making. The Royal Botanic Gardens, Kew, is undertaking a review of its collections to assess the conservation value of those threatened species cultivated at Kew. This is only possible when good quality data on the wild status is available and that, in turn, is supported by information on in-country conservation activities. Where this information is available it is possible for such collections to contribute directly to existing conservation projects in other regions.

The project described here was made possible through the support of a number of agencies in the USA, namely the US Fish and Wildlife Service (Hawai'i'), The Center for Plant Conservation (St Louis) and the Waimea Arboretum and Botanical Garden (Hawai'i'). As a result, seed of the endangered Alsinidendron trinerve has been repatriated from RBG Kew to Hawai'i'.

Plants of Alsinidendron trinerve have been in cultivation at Kew since the early 1960s. The plants are derived from seed collected in Hawai'i' by the famous botanist and collector Joseph Rock. The seed was collected from a population on Mount Ka'ala, the highest point on Oahu. Subsequently Kew received seed (1994) from Berlin-Dahlem Botanischer Garten. The origin of this stock has yet to be traced. At Waimea the species has been in cultivation since the early 1970s, with the first accessions from Pohale Gulch in the Waianae Mountains. The accessions did not survive in cultivation and this population has subsequently become extinct. In 1987 an accession was received as seed from Waieli, this did not germinate. The two most recent accessions came from the Nature Conservancy, both from the currently extant population. Seed was also received from botanic stock grown at the Botanisk Institute of the University of Aarhus, Denmark and the botanic garden at Marburg, Germany. Both accessions grew for three years in the nursery at Waimea but were subsequently lost.

In Hawai'i', the plant has been forced to the edge of extinction. By 1989 only 20 plants survived in the wild. Predation by introduced animals and competition with invasive exotic plants, such as the introduced blackberry (Rubus) have further reduced the wild population to only 7 individuals on Mount Kalena.

The value of the plants in the collection at Kew was recognised by David Orr of the Waimea Arboretum and Botanical Garden. This garden is collaborating with the Nature Conservancy and developing cultivation protocols for this montane species in special air-conditioned facilities. Verification on the wild status of the species and appropriate contacts in Hawai'i' was received from the Center for Plant Conservation. As a result of these contacts the Royal Botanic Gardens, Kew, was able to supply seed of Alsinidendron trinerve to the US Fish and Wildlife Service (Pacific Islands Office) to contribute to a species recovery and re-introduction programme. The seed was supplied to Waimea Arboretum & Botanical Garden, Lyon Arboretum and the National Tropical Botanical Garden.

Cultivation

The plant presents few problems in cultivation. A semi-woody perennial, it flowers well at RBG Kew between October and May. After flowering it is cut down to the base and allowed to re-grow. Plants are grown in the Temperate Nursery in a mixed collection, a temperature regime with a night minimum of 12.5ºC is maintained. Plants are grown in full light. Plants grown in the Palm House at Kew are at a higher temperature (night minimum of 20ºC) and at lower light levels. At Waimea plants are grown in an air-conditioned room where the temperature is kept lower than the external ambient. Extra humidity to compensate for the drying effect of the air-conditioning is provided by regular spraying of water onto gravel filled troughs. At Kew plants are successfully grown in a loam and coir based compost (7 parts of a 50/50 fine loam and grit mix; 2 parts coir; 1 part additional grit; 5 parts fine bark; plus fertilisers).

Propagation

Alsinidendron can be propagated by vegetative means and from seed. At Kew, tip cuttings are taken in early summer and placed under mist at a minimum temperature of 21ºC. Seed is easily raised and fertility is usually high. At Waimea, the seed is sown onto a layer of finely chopped sphagnum moss on top of a 50/50 mixture of silica sand and potting compost. The seeds are sparingly sown over the moss and watered in with a very dilute solution of a metalaxyl based fungicide to prevent Pythium and Phytophthora problems. The sphagnum keeps the seed moist to encourage germination but protects the seed from excessive moisture.

Pests and Diseases

Alsinidendron trinerve in a glasshouse environment at Kew appears to be very susceptible to western flower thrip, Frankliniella occidentalis, and red spider mite, Tetranychus spp. Both pest species can disfigure the plant but do not prevent propagation at low levels of infestation. A regime of integrated pest management is practised at the Temperate Nursery with Amblyseius spp. and Orius spp. used as predators against thrips. Phytoseiulus persimilis and Therodiplosis sp. are used to control red spider mite. As a last resort, nicotine fumigation is used.

At Waimea, insects are swabbed off with dilute alcohol and periodically plants are dipped in solutions of Safer soap (a surfactant and insecticide based on potassium salts of fatty acids) and Avid (a miticide with active ingredients hexanol and avermectin B1).

Conclusion

This species is now established in cultivation in Hawai'i'. As a result, reintroductions planned can take place utilising a numerically secure cultivated stock. The genetic status of the stock is currently being investigated. It is likely that the cultivated stock from Europe is derived from a small founder stock and had subsequently been subject to a number of repeated population bottlenecks.