Defying a `death wish'

Nelson

It's on the verge of extinction with an uphill battle for its survival, but a new push is being made to rescue a little plant native to Tasman Bay, as Vanessa Phillips reports.

Motueka herb grower Yoka De Houwer admits to being a tad scared when she was handed the precious seeds of a critically threatened native peppercress and tasked with trying to help keep alive this kakapo of the plant world.

The coastal peppercress Lepidium banksii seems to have a death wish, say Department of Conservation staff who have been involved in an epic struggle during the past 20 years to ensure the survival of the plant, which is now found naturally only on the Tasman Bay coastline.

"It's the most time-consuming plant that I have dealt with," says Motueka-based biodiversity ranger Roger Gaskell, who works on the plant with colleagues Shannel Courtney and Simon Walls. "I spend hundreds of hours monitoring it, fertilising, propagating, weeding and report-writing."

The peppercress is an unassuming member of the cabbage family but has an interesting history, and is even thought to have been used medicinally by Captain James Cook in 1770.

After two decades of concentrated efforts, successes and frustrations by conservation rangers, Tasman Bay Herbs and chief herb grower Yoka have joined the fight to keep the peppercress alive, and things look promising.

Lepidium banksii is one of 15 species of native lepidium. It is one of 28 nationally critically threatened plant species in the Nelson-Marlborough conservancy.

The peppercress is endemic to Tasman Bay and the inner Marlborough Sounds, although it is believed to be naturally extinct in Marlborough.

Roger says it's highly likely that Captain Cook, with botanist Joseph Banks (whom the cress is named after) on board, collected "boatloads" of Lepidium banksii and a closely related cress, Lepidium oleraceum, known as Cook's "scurvy grass", in the Marlborough Sounds. Cook, probably with the help of Banks, recognised peppercress as part of the cabbage family (Brassicaceae), and was well aware of the plant's vitamin C benefits to prevent scurvy.

With its pungent peppery taste, Lepidium banksii wouldn't have been the most popular dish on the onboard menu.

"By all accounts, the crew didn't like to eat it at all, but the officers ate it, and (the crew) decided `If it's good enough for the officers, we have to have some too'," Roger says.

"That was one of Cook's great achievements - being able to spend three years at sea and prevent death by scurvy. Undoubtedly (peppercress) would have been part of the success of his health regime while he was in this part of the world."

The peppercress was then collected in 1827 from the Tasman Bay coast by French explorer Dumont d'Urville and his naturalist Rene Lesson. It was these records that the species was formally described from in 1899.

However, when Harry Allan wrote about it in the botanical bible Flora of New Zealand in the 1950s, he couldn't locate a living plant.

"It was found by Cook and d'Urville, but then disappeared from view, and it wasn't seen again until 1961, in Totaranui," Roger says.

Botanist Alan Esler collected it then but mistakenly thought it was Lepidium oleraceum. It wasn't until many years later, in 1988, when his specimen's true identity was realised.

That sparked a survey by DOC around Totaranui, during which 11 plants were found. A year later, several plants were found in the Waimea Inlet, which brought the known total to about 20 plants.

"The alarm bells were ringing, and there was quite a bit of concern about how to save this plant from tipping over the edge," Roger says.

It wasn't going to be an easy battle, but rangers were delighted when, in 1994, 500 plants were found growing in the granite sand above the high tide mark at Mutton Cove, at the northern end of Abel Tasman National Park.

The plant is "full of mysteries", Roger says. The find was made following a large drought, which is thought to stimulate the peppercress to produce a copious amount of seed.

The joy was short-lived, though, because the 500 plants were soon wiped out by feasting wild pigs - one of numerous threats to the peppercress, along with possums, deer, diamondback moths, aphids, cabbage white butterflies, viral and fungal diseases, drought, and saltwater flooding.

During the 1990s, hundreds of plants were grown from seed from the few wild plants that were known, and planted out mainly along the Abel Tasman coast. Most died within one season, and some didn't even make it through summer.

"In 20 years of management and survey of this plant, we only ever got to 350 plants (growing in the wild). Now there's about 150," Roger says.

A slightly woody plant with a rambling habit, the peppercress doesn't like shade and has only ever been found within metres of the high tide mark.

Thought to have evolved as part of the seabird ecosystem, it needs plenty of open space and has a high nutrient requirement, which it gets from guano, or seabird excrement.

The plants can live for 10 years and can grow quite rapidly in late winter and spring. They produce a mass of tiny white flowers from late spring to midsummer.

In late summer, the plant loses its leaves, dries out and dies away to a root stock, reemerging in the winter.

DOC staff have found that healthy peppercress plants raised in their nursery and planted out in the wild often fail due to drought, pests or diseases, or "burnout" by the plant itself. Smaller plants have lasted longer.

"This plant has been described as a basket case or a plant with a death wish," says Roger, who adds that the work to save it involves a real mix of "exasperation and TLC (tender loving care)".

Cyclone Dreena in 1997 caused slips and landslides that smothered some good peppercress sites around Totaranui, while habitat loss, with virtually extinct mainland bird populations, has also contributed to the diminishing numbers.

Tonga, Adele and Fisherman islands in the park, from which rodents have been removed, still have good penguin populations, so rangers are pinning their hopes on finding suitable places for peppercress on those islands.

However, like everything else involving this plant, it's not quite that simple.

"We've been planting it for quite a few years on Tonga Island and there's quite a big population of seals, and they occupy every square inch of flat ground on Tonga Island. A lot of the plants are crushed, so it's a matter of finding a tiny little spot where they might have the right space and the right nutrients," Roger says.

"Even though we've been managing it for 20 years, we still don't know what the secret is to this plant, and we're still experimenting with a mixture of soil types, habitat, shade, rocky coast, sandy islands or pebbly islands."

The peppercress is managed at seven sites in the Motueka area and at a few sites north of Totaranui, and a planting done by DOC on Maud Island in the Marlborough Sounds in 2006 and is thought to still be alive.

Although keeping the peppercress alive in the wild has been challenging, based on some success, DOC's new strategy is to collect a lot of seed and sow it into the landscape and let nature take its course.

This is where Tasman Bay Herbs comes in. It has taken on the challenge of growing the peppercress for seed production, and now has more than 600 plants growing at its site near Motueka.

The best plants, only a few months old, are thriving in the greenhouse under hydroponic conditions, although Yoka is also experimenting with growing them outside and in an outdoor covered area, to compare growth.

Yoka co-owns Tasman Bay Herbs with Don Grant, and both are interested in conservation. They learned about the bid to save the peppercress two years ago and offered to help. Late last year DOC accepted their offer, to try to boost seed production.

"They turned up before Christmas with 50 plants and a whole lot of seeds. We were all too scared to touch them," Yoka laughs.

However, she soon got stuck into sowing seeds, which she has found are easy to grow in the company's controlled environment.

Genetic sampling of the known plants has been done to try to establish the genetic diversity, to help the fight for their survival, and community groups are being encouraged to become involved in the hands-on work to maintain habitats for the plant.

Roger doubts that there will ever be masses of the peppercress growing in the wild, but says it would be good just to get small, stable populations in the region.

There's no doubt that the peppercress would be extinct by now without the management during the past 20 years, but it has to be asked - if this plant has a death wish, why bother with all the effort trying to save it?

"The same answer could be applied to the kakapo or the kiwi," Roger says.

"It's part of the botanical diversity and the botanical jigsaw of the region and of the flora of New Zealand."