While much is known about the plight of New Zealand’s endangered birds, it’s fair to say our plants don’t always receive the same degree of attention. There tends to be a focus on the cute and cuddly, not just in New Zealand, but internationally. In reality though, 14 per cent of our more than 2700 native plants are threatened in the wild. Many have already disappeared, but thanks to the work of a dedicated bunch of individuals since the early 1940s, the tiny, inconspicuous Castle Hill buttercup (Ranunculus paucifolius) still clings to existence.
The curious Castle Hill buttercup, also affectionately known as ‘Little Frog’, is confined to a six-hectare gently sloping amphitheatre of limestone debris surrounded by limestone cliffs, tors and boulders at an altitude of 760 m. Nestled west of the Castle Hill homestead, it’s located in the Southern Alps between the Craigieburn and Torlesse ranges, where temperatures range from -15 degrees in winter to 36 degrees plus in summer. Once covered by tōtara and tall shrubs, the area was cleared by fire 600 years ago, replaced by tussock and pasture.
Rarely more than 10 cm tall, for the most part the buttercup is characterised by its little fleshy greyish-green to ashen-purple coloured deciduous leaves. In winter it hunkers down, hiding underground from the extreme cold, only to re-emerge in spring. Between late October and November, it bursts into colour with a dense mass of round-tipped golden flowers, each with between five and eight petals 2.5–5 cm in diameter.
Castle Hill’s early owner and amateur botanist, John Enys, was the first to notice the buttercup was unlike anything else he’d seen. Years later, Dr Lance McCaskill, a university lecturer in Christchurch, was integral in establishing New Zealand’s first reserve, formed specifically to protect a plant – the Castle Hill buttercup. Gazetted as a ‘Reserve for the Protection of Flora and Fauna’ in 1954, it was renamed the Lance McCaskill Nature Reserve in 1987 in recognition of his work.
Even before it was gazetted, McCaskill took carloads of students up to the area to help him erect a predator-proof fence in a bid to create a safe ecosystem for this bio-diverse hotspot. Monitoring of the buttercups started in 1949, making it New Zealand’s longest running monitoring project, staking, numbering and fencing clumps of plants.
Following the seasons, he and other buttercup enthusiasts would painstakingly weed the limestone slope, collect seeds and sow them in situ, and once the seedlings had set, they transplanted them to new plots at Castle Hill. Prior to the fence being erected, numbers may have been as low as 32 plants; by the late 1970s numbers had risen to possibly 300 individual plants.
McCaskill also sent rare buttercup seeds to botanical gardens in New Zealand, and overseas to Kew in London and the Royal Botanic Garden Edinburgh in Scotland, but it proved a fickle exercise with researchers reporting the seeds were hard to strike, and domesticated plants did not live as long as they do in the wild. Despite McCaskill’s meritorious efforts, the numbers continued to plummet. He commented that ‘This strange plant is passing slowly [and] unreluctantly away before our eyes in an age-long euthanasia.’
Today, only 63 plants remain. With the Castle Hill buttercup’s future teetering perilously on the edge of extinction, Department of Conservation’s threatened plant ranger, Daniel Kimber (Danny), has picked up the mantle and is continuing McCaskill’s work.
Danny joined DOC as a trainee ranger in 2004, falling into the role as threatened plant specialist. ‘I studied birds at university, but I am colour-blind, so I couldn’t do the bands. I am not a botanist. I’m a ranger that does plants,’ he explains. While it wasn’t his first choice, it hasn’t diminished his passion for what he does.
‘I have 17 separate plants [species] that I look after. These are the worst of the worst; they are very, very rare in a global sense. I have others that are just as dire. In reality, I could be doing 60–70, but there’s just me. If we had more rangers and more capacity, we could do a lot more, but what drops off? It’s a big juggling act. What we need is for the public to recognise that while you do have your lovely, cuddly kākāpō, there are plants out there that are in even more trouble.’
The Castle Hill buttercup is one of 11 of those 17 threatened plant species which are found in the Waimakariri Basin. Despite decades of work though, Danny says there remains many unknowns surrounding the buttercup.
‘We know that a lot of the plants are over 100 years old. It’s a long-lived species, but the fact that they are not reproducing naturally is of massive concern,’ he says. ‘There hasn’t been a plant pop up naturally in the past 30 years. Of those 63 left, there’s only 43 that are contributing to the population because the others don’t flower. No flower equals no seed. And we don’t know why. After two years of trying we do know that they can’t pollinate themselves though.’
DOC’s been actively trying to breed the Castle Hill buttercup to help boost the numbers with limited success. ‘Each year we take a percentage of seed from them to the native plant nursery at Motukarara where they do their best to propagate them, but it’s fraught with difficulty. We might get two or seven or more. Our best year was nine, seven of which we still have now. Since 2000 we’ve grown 16 (total) of which we have 13 left. Of those seven plants grown in 2017, only two flowered this year.’
Seed viability remains a big issue. In 2015 every seed was lost to mice, and with such a short flowering window, you have to time it perfectly, says Danny. Competition from invasive weeds is currently the single biggest threat to the buttercup, but in the past, hares have also proved deadly – so much so, that DOC has installed a $100,000 custom-designed 6-ft high hare-proof deer fence to keep them out. This year it has also done $50,000 worth of dedicated hand-weeding and upped the rodent control.
Although the reserve was ultimately established for the buttercup, Danny says the upshot has been huge for a whole range of flora and fauna. At least 12 other plant species are benefitting including the nationally threatened Castle Hill forget-me-not (Myosotis colensoi). Native skinks and geckos are also thriving in the area, and it goes on from there. They’ve also discovered a rare snail, and grasshoppers within the reserve.
While the odds are stacked against the buttercup’s long-term survival, Danny has vowed it won’t happen on his watch. ‘We know it’s a plant on the way out, so the pressure is on. We can’t walk away.’ He’s confident that with more research, they’ll find the answers, averting possible extinction – for now at least.
[ WORDS + IMAGES Annie Studholme ]