This story was first published in Open Space issue 107 in November 2024. You can read the full issue, as well as previous issues of Open Space, on our website.

Our thanks for the research, contribution and words of Aalbert Rebergen, Dave Craw, Cathy Rufaut, Dhana Pillai, Steve Read, Rob Wardle, landowners Charlie Hore and Belinda Colling and previous landowner John Beattie.

At a distance, the Patearoa inland saline site protected by a QEII covenant looks like many of the other landscapes in Central Otago – dry, rugged hills and wide expanses of light ochre grasslands.

But up close, and below the surface, a very unique ecosystem is at play, all dependant on the specific salinity (salt levels) of the ground beneath.

“When people think of environments protected by QEII covenants, they might first think of wetlands and forest remnants,” says Rob Wardle, QEII regional representative for Central Otago. “But the Patearoa covenant is something a little bit different from what usually comes to mind.”

At only 4.5 hectares, the small covenant at Patearoa protects what is called an ‘inland saline’ environment or ‘salt pan’, which is home to some extremely unique flora and fauna.

Jobs for Nature funding via the Department of Conservation has opened up exciting research at the Patearoa as part of QEII’s Eastern South Island Rare and Threatened Species programme, overseen by Aalbert Rebergen. This funding has enabled researchers to survey covenants that have especially rare biodiversity values and paved the way for improving management of the sites.

Professor Dave Craw from the Geology Department at the University of Otago has been involved in research centred on the Patearoa site.

Dave explains that salt pans like the ones at Patearoa are formed from small amounts of dissolved sea-salt delivered to the inland environment in rain and wind from the coast. Salts are left behind when rain and shallow water runoff evaporate during Central Otago’s well-known high summer temperatures.

The salt pan forms because of a combination of factors. The presence of clay underground, the bare soil-free surface that is constantly eroding via wind and water, and the dry, highly evaporative climate all contribute to the buildup of salt on top of the bare ground and in shallow ground waters.

“The most common salt mineral [at the site] is sodium chloride, the same as table salt,” says Dave. “In addition, some of the rainwater interacts with the schist bedrock, and dissolves even more chemicals, especially more sodium. This excess sodium combines with carbon dioxide from the atmosphere to make sodium carbonate minerals, similar to washing soda used in some laundry powders. This can make the surfaces highly alkaline, with pH as high as 11 (that is 10,000 times more alkaline than drinking water).”

There are other salt pan areas in the general Maniototo area, but they are geologically different and are affected more strongly by surrounding agriculture, especially irrigation. It is possible that the Patearoa site may be the last example in the Maniototo of this type of landscape and its flora, with associated invertebrates. Native bees seem to love the bare ground of the pans, seemingly not put off by a salty interior to their burrows.

Most plants would dislike living in such a harshly saline-alkali environment, but there are several species endemic to New Zealand that have adapted to grow and thrive in saline environments, called halophytes (halo meaning “salt” and phyte meaning “a plant growing in a specific way or place”).

These salt-tolerant species can also grow along the coastline, but their habitats have been decreasing and many of these halophytes are now classified as rare or endangered. The salt grass species Puccinellia raroflorens – a tiny, often sand-covered grass – may now be limited to only inland sites such as at Patearoa.

Some exotic weed species such as buck’s horn plantain (Plantago coronopus) are also salt and drought tolerant, and can displace the endemic plants, encroaching on their habitat and changing the chemistry of the earth beneath. As the weed grows it creates an organic layer of ‘soil’ on the surface of the clay salt pan, which has a lower salinity. Over time this surface layer builds a foothold for exotic pasture grasses to become established, creating even more low-salt surface ‘soil’. As a result, the salt pans are shrinking steadily.

Protecting something a bit different

John Beattie, who first protected the Patearoa site with a QEII covenant, has a longstanding interest and fondness for the salt pans. John’s grandfather bought Patearoa Station in 1910 and the property remained in the family for over a hundred years. As a child, he remembers Otago University students camping near the salt pans during Labour Weekend to study the flora and fauna of the site.

“We were told lots of different stories from the experts, including that it had been an inland sea, but then that idea was quashed, and it turned out the salt was from the soil,” says John. “There was always interest from the scientists.”

In the mid-nineties, Brian Molloy, the QEII regional representative at the time, approached John about protecting the Patearoa site with a QEII open space covenant.

“[Brian] was quite a well-known scientist in the region, in the high-country scene,” says John. “He was the first person who came to talk to me about where the [covenant] site was planned to be.”

Fast-forward to the present day, and QEII rep Rob Wardle works with current owners Charlie Hore and Belinda Colling to continue the management of the area. Cattle have been excluded and a low level of sheep grazing retained to achieve some control of exotic grasses and herbs, which outcompete natives.

Scratching the surface

During their study of the site, researchers found a ‘salt line’ at Patearoa – a separation between the plant species due to the geology underneath. Above the salt line, the environment is more favourable for non-saline species, such as Maniototo peppercress (Lepidium solandri) and some native broom (Carmichaelia spp). The endemic salt-tolerant plants or halophytes are only found below the salt line, like Buchanan’s orache (Atriplex buchananii).

“The salt line arises because of the underlying geological structure, with impermeable clay-rich rock below the salt line and rubbly permeable debris above the salt line,” says Dave Craw. Researchers documented the plant species above and below the salt line revealing that there is very little overlap between the salt-tolerant and non-saline plant species.

Below the salt line, Dave Craw and the research team noticed that shallow excavation or ‘scraping’ of weedy areas revealed that saline rock remained below the surface, underneath the primitive soil created by the weeds. They decided to do a pilot study of this scraping method to see if the endemic salt-tolerant species would grow back on the bare salt pan surface once the weedy soil had been scraped away.

“We removed the ‘soil’ from the area in late 2022, to re-expose the soil-free bare ground again,” says Dave. “At the same site in April 2024, we saw rampant colonisation by one of the endemic salt-tolerant species, Buchanan’s orache (A. buchananii). Encouragingly, the weeds have not yet returned to any significance in the scraped trial areas.”

This pilot study gives a small glimpse of what can be achieved with future management of this site. “One of our new scraped areas was developed where the spring-annual Myosurus minimus was last seen at the site 20 years ago,” says Dave. “We are hoping for return of that from a seedbank below the Buck’s horn plantain (P. coronopus) weed cover.”

The harsh, saline environment at Patearoa might not seem like an obvious safe haven, but for some of our most rare and endangered salt-tolerant plant species, Patearoa could be the lifeline they need to stave off extinction. Perhaps one day the unassuming shoots of the New Zealand mousetail (Myosurus minimus) will emerge for the Central Otago spring.

Some like it salty

Some of the flora and fauna found at the Patearoa inland saline site.