A Study Tour of the Hawaiian Islands
By Nick Biddle
During the summer of 1996 I spent a month on a study tour of the Hawaiian Islands. I visited four of the eight main islands; Oahu, The Big Island, Maui and Kauai. I visited 13 botanic gardens, National and State Parks and nature preserves as well as hiking in natural vegetation with local people and attending the two day Hawaii Conservation Conference. I was treated royally throughout and had the time of my life; not only because of the amazing and unique flora of the islands, but also thanks to the wonderful people I met there. The following is an extract from my Travel Scholarship Report.
Haleakala National Park
My principal motivation for visiting the island of Maui was to see the Haleakala Silverswords (Argyroxiphium sandwicense subsp. macrocephalum). This is a celebrity species which acts as a symbol of Hawaiian conservation. Their striking appearance and spectacular flowering is set off to perfection by the strange landscape they inhabit. When I first saw a postcard of the Haleakala Crater I was sure the photographer had been a little over enthusiastic with the filters, but it is in fact largely made up of black, dark green and orange-red cinders.
One problem these plants do not currently suffer from is competition from other plant species. They are adapted to a most extreme climate, endemic to the Haleakala Crater at elevations between 6,500 and 10,000 foot. Concave hairs reflect the searing sunlight and an intercellular gelatinous substance stores water and helps to prevent freezing. By 1920, however, they were believed to be near extinction, due to the combined effects of browsing by goats and cattle, and the habit of visitors removing whole plants as trophies to signify that they had reached the summit. Under legal protection since then, population numbers have risen from an estimated 4,000 in 1935 to a current figure in excess of 64,000.
The biggest threats at present are the possible invasion of non-native mullein (Verbascum thapsus) and fountain grass (Pennisetum setaceum) from neighbouring islands where they occupy similar habitats. More pressing than that however is the Argentine Ant (Linepithema humile) which has colonised the area, threatening the endemic arthropod fauna, including pollinators which evolved in the absence of ant predation. Research has shown that the Silverswords require cross-pollination for successful seed set and are therefore reliant on their pollinators. A marked expansion in the ants’ range was noted in 1993. If not controlled, this species could have potentially catastrophic effects on locally endemic biota, including Silverswords.
Silverswords are monocarpic; they flower once only and then die. The flower-spike appears as if it has erupted from the globe-shaped spiky silver rosette. Each one typically bears hundreds of capitula; daisy-like heads with maroon disc florets and yellow ray florets. The proportion of the population which flowers each year is quite variable. The environmental stimuli for flowering or non-flowering are still unknown. It is believed that root disturbance stimulates flowers (Loope pers. comm.), perhaps as an association with volcanic eruptions. An apparent relationship of the 1991 mass flowering event to stratospheric alteration by the eruption of Pinatubo Volcano in the Philippines is intriguing.
To see flowering Silverswords for the first time is a fantastic experience, but the real treat was that the last night of my scheduled stay on Maui was the night of the full moon, and I was able to join a Ranger guided hike into the Crater to see wild populations by moonlight.
The quality of the restoration work at lower altitudes is also remarkable. What was once over-grazed and impoverished has been returned to native scrub. The method of goat control is simple but ingenious. Six Judas Goats with radio collars, all male, are kept within the Park Goats are naturally gregarious, so when other goats do penetrate the encing they will socialise with the Judas Goats. Whenever the herd exceeds six, the interlopers are dealt with.
The many miles of trails are interpreted by excellent signage and guide leaflets. Camping is free and well serviced. The quality of the Ranger guided hikes is superb.
(`Travel Scholarship Report: A Study Tour of the Hawaiian Islands, Summer 1996′ by Nick Biddle is available at the School of Horticulture, R.B.G. Kew and the R.H.S. Lindley Library, Vincent Square.)