The endemic and endangered plants of limestone outcrops in the Waitaki Valley
Neglected by a lack of resources, public interest and advocacy for their protection, limestone outcrops in the Waitaki Valley and across South Canterbury are home to a suite of endemic plants, including some of New Zealand’s most endangered species.
THE IMPORTANCE OF LIMESTONE AREAS FOR
their remarkable fossil records and Māori rock drawings has long being known in the Waitaki Valley and parts of
South Canterbury. Until recently, the fate of its equally unique vegetation had been left in the hands of the gods and that of a few passionate people who have spent hours removing nasty weeds, manually, around threatened plants and building relationships with landowners. But the tide looks to be turning with a new team from the Department of Conservation (DOC) and fresh department investment aiding the fight.
More than 23 million years ago, when warm shallow oceans covered most of New Zealand, these limestone areas were part of the ocean floor. Formed by shells and skeletons of billions of small organisms being pressed into the soft rock over a long period of time, they contain the richest known marine fossil recorded from the Oligocene period, a pivotal time in the evolution of many of today’s whales and dolphins.
With the changing land and sea levels the limestone was raised into open air. It formed distinctive flat-topped and steep-faced landforms that were constantly eroded by wind and rain, leaving these incredible pavlova-coloured limestone outcrops.
Each limestone area varies in the type of limestone present, the climate they experience and the plants that cover them. Its old age coupled with unique physical and chemical properties makes limestone a challenging environment for species to survive in. Separated like islands, over time, each area has evolved its own unique set of limestone-inhabiting species.
Limestone’s wealth as a building material is undeniable; it is seen in almost every town and city across New Zealand. It is also used in the creation of cement and extensively in farming as fertiliser. Quarrying of limestone sites has undoubtedly played its part.
Although the earliest cetacean fossil was discovered in the area by naturalist Walter Mantell in a creek bed near Ōamaru in 1848, it wasn’t until the 1990s that the uniqueness of the plants inhabiting the limestone castles near Kurow were first recognised by botanist Brian Molloy. He revisited Awahokomo several times, noting a total of 16 species of endangered plants. Due to its significance a Queen Elizabeth II (QEII) Covenant was established in 2000. He also visited many other limestone sites.
Since those early days, DOC negotiated with private landowners to purchase two significant limestone sites in the Waitaki Valley, establishing Wai O Toura (Gards Road) and Waipata (Earthquakes) reserves in a bid to protect threatened habitats and the rare and endangered species they’re home to.
Both Wai O Toura and Waipata contain a handful of threatened species including the perennial herb, Earthquakes gentian Gentianella calcis, an Earthquakes subspecies, endangered native broom Carmichaelia hollowayi, and the tiny fern-like native cress Lepidium sisymbrioides.
Awahokomo remains home to six rare species including
the only population of the critically endangered Awahokomo cress Pachycladon exile. Recognised as the sixth most endangered species in New Zealand, the population is estimated at between 11 and 130 plants.
South Canterbury also hosts many important limestone sites, but most are on private land. South Canterbury has at least six endemic calcicolous plants (plants that only live on limestone), only occurring on limestone within the region, and the majority are at serious risk of extinction. These include gentians Gentianella calcis subspecies manahune and subspecies taiko, limestone bittercress species Cardamine caesiella and Cardamine integra, the recently described Geranium socolateum (which also has a small population in North Otago) and the Manahune buttercup Ranunculus callianthus.
Under the Significant Natural Areas (SNA) Project completed in 2016, about 90 per cent of the limestone areas in the Timaru District have been surveyed. But though the SNA reports contain species lists and give some information on the particular ecosystem, threatened plants, other values and issues such as weed infestation, they provide little data about particular taxa, says local naturalist, researcher and photographer Hermann Frank. ‘We need better data about the exact distribution, state of populations and particular threats.’
Hermann has worked tirelessly promoting awareness of the importance of the limestone ecosystems for more than a decade. Much of the work has largely been undertaken by volunteers and local iwi, though QEII, DOC and the Timaru District Council have also contributed funds and manpower to weed control projects and erecting enclosures.
‘Generally, the limestone areas and habitats haven’t received much recognition. People weren’t aware of what was there. Landowners particularly, didn’t realise what they had on their properties. Some landowners are very excited about what they have, whereas others have different priorities. But once
South Canterbury has at least six endemic calcicolous plants, only occurring on limestone within the region, and the majority are at serious risk of extinction.
they are aware of them, they are generally happy to protect them.’ Most are now on board with protecting those areas and the plants.
To date though it’s been hampered by a lack of knowledge and funding. ‘Unfortunately they [limestone plants] are not something that jumps out at you,’ says Hermann. ‘They are pretty inconspicuous when they are not flowering and even then it’s much more difficult to show or tell someone what they should do for a particular plant compared to a bird.’ But he’s not giving up.
It’s hoped new work being done at Wai O Toura (Gards Road) and Waipata (Earthquakes) reserves could provide the blueprint on how best to protect and manage these rare ecosystems across wider Canterbury going forward.
Both areas were fenced off from stock to protect them from further grazing after they were purchased. Gards Road has been managed quite intensively since purchase and before with removal of the majority of boxthorn and monitoring of threatened plants. Earthquakes meanwhile, has had little to no weed control to date, but some small-scale monitoring and management of the threatened species.
DOC science advisor Clément Lagrue says pressures on the ecosystem and their impacts reflect on the threat status of these plants. While intensive grazing may have had detrimental effect, competition from introduced weeds
and grasses like red fescue, cocksfoot grass, mouse-ear hawkweed, viper’s bugloss and stonecrop remain the single biggest problem facing limestone plants, Clément explains.
There are still so many unanswered questions when it comes to calcicolous plants, and it’s his job to design research to find the answers. ‘It still means that we could lose them before we know anything about them really, which is part of the problem. We know so little, that protecting them is even more challenging when you don’t know their autoecology or what insects pollinate them, for example. Which means that these sites almost certainly hold other underestimated ecological and biological values such as native invertebrates (native bees, reptiles, high diversity of native snails).
‘Most of the sites are in an ocean of farmland, whereas they were once surrounded by forest,’ he says. ‘At the moment we are just babysitting what we have got, but that’s not a solution long-term as it’s unsustainable. If we can turn the tide on the ecosystem as a whole in a more holistic way, then the plants should follow. We are past the manage and protect for the very large, if not all, of them and more into a recovery and restore approach now. In a way, my work is to lay out and test the blueprint to the road for recovery. Even if it’s a long and winding road.’
‘ Most of the sites are in an ocean of farmland, whereas they were once surrounded by forest.’