Conservation Comment: Bring back this thorny native

Thorn tree: A large matagouri near Mt Cook

Which native shrub was abundant in the Whanganui district when European settlers arrived but is now extinct here? The answer: matagouri (Discaria toumatou). No other native shrub has been reduced so much in the North Island in the past 150 years or so.

Matagouri is New Zealand's only thorny native shrub. Its rigid spines, used by Māori for tattooing, can puncture tyres and soft tissues of dogs, horses and people. Farmers have often regarded it as an impediment to cultivation and stock movement.

However, like legumes, matagouri can fix atmospheric nitrogen, using micro-organisms associated with its roots. That benefits surrounding plants.

A few years ago, while surveying vegetation in the Mackenzie Country, I found a farm in the Ahuriri Valley with patches of dense matagouri scrub 3-5 m tall. The owner said he encouraged it because sheep sheltered under it, especially during heavy snow. During summer drought, the lightly shaded pasture under matagouri continues growing, benefiting from added nitrogen.

Matagouri is part of a suite of twiggy shrubs still known as "grey scrub" in the eastern South Island, as distinctive a landscape as tussockland and beech forest. Just because it has thorns is no reason to eradicate it.

Today, in pastoral lands, palatable native species of grey scrub have often disappeared, except among matagouri; it also provides protection for native animals like lizards and nesting birds.

Matagouri's seedlings grow in stony or sandy ground with few other plants, which means that matagouri eventually becomes extinct in pasture, through lack of replacements.

In about 1989, I met retired farmer Moore Blyth on dunes near Kaitoke Prison. He said matagouri scrub was so dense there when his parents started farming that it was removed to allow dogs, sheep and horses to get through.

Around 1960, one matagouri was seen nearby by local Junior Naturalists; one shrub was also reported in Waiinu in 1966.

A farm near Foxton had 80ha of matagouri in 1926, reduced to one plant by 1976. Odd shrubs were reported between Bulls and Levin in the early 1900s but, by the 1990s, only two small sites between Taranaki and Paekakariki still had matagouri.

I photographed one near Lake Alice in 1996.

Although it has related species in South America and one in Australia, matagouri is unique to New Zealand. No North Island plants are as large as some tree-like South Island ones. Maintaining genetically different populations in the wild and in different regions is important for future study.

Since we can no longer see wild groves of matagouri in the North Island, it would be wonderful to recreate the effect from near-local stock.

It is a striking shrub, especially if planted in groups with other small-leaved native shrubs or tussock.

When Dr Eric Dorfman was our museum's director, his proposal "Good Nature" (2011) advocated replacing lawn in front of the museum with local native plants.

Matagouri was part of his recommendation because of its decline, cultural uses (tattooing) and its being part of a shrub community that was once the habitat of several species of moa. Whanganui Museum has one of the largest collections of moa bones in New Zealand. Natives were planted but no matagouri — too dangerous, we were told.

Species conservation should be for more than "warm fuzzies" like panda and kakapo.
Could Dr Dorfman's proposal be revived to recreate a piece of Whanganui history with a bed of matagouri near the museum?

The new management plan for Pukemanu/Queen's Park gives us an opportunity.

Colin Ogle

■Colin Ogle is a retired ecologist.