VIDEO: Years-long research suggests alpine plants are about to struggle – and not just because of warming. David Williams reports
The morning rises to meet us.
As we pick our way carefully below Tukino Lodge, our footsteps kicking up dust in the loose volcanic soils and rocks, clouds blanketing the Rangipo Desert and State Highway 1 drift up the eastern flanks of Mt Ruapehu, negotiating rugged valleys carved by lahars.
The stillness gives the rising cloud a ghost-like majesty.
Waterfalls are the dominant sound. Powered by hidden springs, they flow beneath Te Heuheu Peak and the shock-white of the Mangatoetoenui Glacier. These waters are the source of the Waikato River.
At a glance, the surroundings seem bare but beautiful – a moon-like landscape of boulders, rocks and stones atop earth of reds, yellows and greys.
But look more closely. Dotted among the rocks are clumps of ground-hugging vegetation. Needle-like protrusions of tussock, silvery-white flowers adorning cushions of vegetable sheep, and aromatic herbs giving off the scent of fennel.
It is here, in this wind-swept bowl about 20 minutes’ walk from the lodge, that Victoria University of Wellington field ecologist and senior lecturer Dr Julie Deslippe and PhD student Indira Vanessa Garcia Leon are using vegetation plots as windows into the future.
Unfortunately, the news isn’t good.
Internationally, it’s thought plants at this elevation – about 1600 metres above sea level, roughly the same height as Coronet Peak, near Queenstown – are “temperature limited”, meaning they grow at the very limits of life because it’s so cold.
Warmer temperatures would promote growth, it was thought.
“That’s not what we found in Tongariro National Park,” says Deslippe, whose name is said “De lip”.
“We found that, actually, our native plants are really happy at the temperatures they’re growing at, and pretty quickly they are showing signs of decline.
“So that doesn’t bode well for our species. It means that invasive species that are also in the park might be better adapted to the warmer temperatures that are coming in the future.”
The “subduction” of the Pacific Plate, where it slides under the Indian-Australian Plate, has created a line of volcanoes stretching from Ruapehu, at the southern end of the Taupō Volcanic Zone, to Tonga, part of the wider Pacific Ring of Fire.
At 2797m, Ruapehu marks the North Island’s highest point, near which there’s a deep crater containing a hot, acidic lake. The mountain has eight named glaciers – the only glaciers in Te Ika-a-Maui.
The mountain is of huge cultural and spiritual significance. Ruapehu, or Matua te Mana, is central to iwi Ngāti Rangi’s cultural and spiritual identity – he is referred to by uri, or descendants, as Koro Ruapehu, the tribal grandfather.
While volcanic activity started in the Taupō zone about two million years ago, Ruapehu has been active for about 250,000 years. (Its last eruption was in 2007.)
That’s a long time for these slow-growing plants to adapt to an area battered by wind, and challenged by searing summer heat and winter chill.
Deslippe says the Rangipo Desert, adjacent to the Desert Rd, which sits about 1070m above sea level, is a desert ecosystem not because of a lack of rain but because of the quick-draining volcanic and sandy soils.
The area has been dominated by tussock grassland for hundreds if not thousands of years.
“Climatically it should be a beech forest,” she says. “But because of the disturbance history, the volcanism, the fires, and the shifting, eroding sands, it’s been tussock grasslands.”
Higher up the mountain, on a spur away from the usual path of lahars and ash, beech forest is visible.
If that clump of forest is an island in a sea of pressure then so is Tongariro – established in 1894 as New Zealand’s first national park and the world’s fourth. It is bordered by farmland and the Waiouru Military Training Area.
There’s also an introduced plant invader: heather.
In 1912, one of the park’s early wardens, John Cullen, decided, unwisely, the western side of Ruapehu was an ideal place to recreate the Scottish grouse moors. For about a decade, sacks of Scotch heather (Calluna vulgaris) seed were scattered on the central plateau in the hope of turning it into a gamebird shooting area.
The introduction of pheasants and grouse to the park was stopped by public outrage. But heather proliferated, eventually spreading across almost 60,000 hectares by the 1990s.
Heather is hard to control. Spraying it kills other species, including natives, and digging up the plants releases seeds into the loosened soil.
Something had to be done, as heather outcompetes slower growing natives.
In 1996, the Department of Conservation introduced the heather beetle (Lochmaea suturalis) from Scotland as a “biocontrol agent”.
They took years to establish and then spread slowly. Over the last four years, however, the population exploded.
Ecologist Paul Peterson, a senior technician in biocontrol and molecular ecology with Manaaki Whenua/Landcare Research, estimated last year that in the previous three years alone the beetles had killed or severely damaged 35,000ha of heather.
That might sound impressive but Deslippe, casting her eye over the Rangipo Desert, says it’s still dominant: “There’s more heather here than anything else.”
When she talks about invasive species outcompeting natives, she’s talking about heather.
To add another layer of trouble there are climatic changes.
Deslippe says the lee side of Tongariro National Park, to the east of Ruapehu, receives about 15mm less rain than it did 50 years ago, and it’s about 1degC warmer. “That doesn’t sound like a lot but that means a lot less water for plants.”
It took these plants thousands of years to adapt. Now its warmer and drier, and heather has moved in. That’s a lot of change in a relatively short time.
Since the summer of 2014-15, Deslippe and her team have been researching how changes in plant community composition and warming have altered biodiversity, and how this alters the ecosystem functions.
They do that through vegetation plots, about 1.5m square – some clustered on the Rangipo Desert, and others below Tukino Lodge. (On the wetter side of the mountain, Calluna vulgaris can be dense and stand more than six feet tall, which is not ideal for experiments but very good for heather-eating beetles.)
Some simulate warming – using makeshift greenhouses with open tops to still the wind and trap the heat. It simulates a world in which soil and air temperatures are about 2degC warmer, but still get the rain. (It’s predicted Tongariro National Park will be 2degC warmer in 2070.)
There are four treatments: warming with heather, warming with heather removal, heather removal without warming, and a control.
(One plot, almost entirely covered with heather, was known as the “plot of death”. Deslippe says: “It took us a whole day, three people, to cut out all the heather the first time.” After seven years, a smattering of new plants are evident. “That’s all new regrowth,” she says, noting “it’s not fast”.)
It’s an experiment in plant composition. Which will thrive? Will they all survive?
In the warming plots, data loggers track temperature and humidity every 15 minutes. Regular manual measurements show which species are present, the area they cover, and the balance of their photosynthesis (using sun, water and carbon dioxide to create oxygen and energy) against their respiration or “breathing” (burning food molecules for energy), which determines plant productivity.
“We found that plants have species-specific responses to warming,” Deslippe says. “Most of our alpine plants actually don’t like it very much.”
The warming of plants on the Rangipo Desert increases evapotranspiration, and increasing plant stress. “They actually dry out more.”
PhD student Garcia Leon’s is gathering data to prove – assuming this is the case – natives seem more stressed with warming, while invasive species perform better.
“More data is definitely needed,” Deslippe says.
Garcia Leon, who’s from Colombia, started her PhD in March.
She says the world is warming, in general, but climate change can also lead to more extremes, including lower temperatures in alpine areas. So a plant’s thermal tolerance, at both ends of the spectrum, is important.
“The species that are here will have to acclimate or adapt to that as well. And if the invasive species is better at doing that then [it will] become more dominant and surpass the dominant natives.”
Data compiled over seven years maps the species in each plot, how many there are, how many are rare, how dominant the most dominant plant actually is, and how that has changed, including under warming conditions and with the dominant species removed.
“We found low resilience to warming of the [native] species in general, at high elevation and low as well.”
Unfortunately, invasive species are known for their high “plasticity”, or ability to adapt to and cope with changes. What seems to be happening on the Rangipo Desert is heather has a higher tolerance to stress. (Heather hasn’t reached the higher elevation area near Tukino Lodge.)
That’s a double whammy, squeezing native plants from habitable space.
Garcia Leon: “With more warming we will have higher potential of the invasive species to take over the plant cover.”
The natural consequence, according to Deslippe, is native plant species will decline in abundance and it will be harder, in the future, to conserve native biodiversity.
But Aotearoa’s biological diversity is already in trouble, which is a big problem for a country in which about 80 percent of plants are endemic, meaning they’re found nowhere else in the world.
If we don’t look after them no one else will.
Yet our wetlands, where many native plants live, continue to be drained and pressured by exotic invaders. On our coast, the decline of seabird and marine mammal colonies has caused ecological changes and degradation of dunelands.
Inland, in rocky habitats, areas of scrub, in tussocks and herbfields, and lowland forests, higher vascular plants, like trees, grasses and flowering plants, are becoming fragmented, not least because the birds and animals that usually carry out pollination and seed dispersal are no longer there.
The country’s biodiversity strategy, released in 2020, says around 4000 species are threatened or at risk of extinction. “We need to act urgently to ensure that nature is healthy and thriving for its own sake and for current and future generations,” the then minister, Eugenie Sage, said in the strategy’s foreword.
Globally, a million animal and plant species are “perilously close to extinction”, says an editorial in The Guardian. Yet, as the newspaper rightly points out, “our human fate is ulimately bound up with nature”.
At the opening of the United Nations’ biodiversity conference in Montreal, Canada, earlier this month, UN secretary general António Guterres described humanity as a weapon of mass extinction, and called government to end the “orgy of destruction”.
How many species is it “acceptable” to lose?
This isn’t some abstract issue. Biodiversity is crucial for nature’s life-giving services: clean drinking water, clean air to breathe, food to eat, fibres to make our clothes, and to burn to keep us warm. Natural capital, if you like, sustains human society.
Yet the rate of biodiversity decline is the highest since the last great extinction, when dinosaurs were wiped from the face of the earth. A major factor is warming – and alpine areas, like the North Island’s central plateau, are warming much faster than the global average.
Species will have to evolve or adapt where they are now, or move to cooler climes upslope. That’s easier said than done.
Deslippe says in a perfect world plants would grow deeper roots to access more moisture – but only if there’s enough rainfall. Perhaps it could spread laterally and get lower to the ground, so the wind doesn’t dry it out so quickly.
“But if the ground is covered with an invasive weed that out-competes it, it can’t do that. So what we’re seeing is these multiple drivers, species invasions, disease outbreaks, new insect pests, warming, and drought are major drivers of decline, often not singly, but in combination.”
The Department of Conservation has a legal duty to manage land for conservation purposes.
In a statement, Jenny Hayward, DoC’s Tongariro biodiversity supervisor, says it has not specifically changed its programme because of Deslippe’s research.
“Biocontrol beetles are making a significant impact on invasive heather and we manage incursions of other invasive plants as they occur.
“While this mitigates short-term risks to threatened plants, climate change is a longer term problem for which we are still considering strategies.”
Deslippe says if changes are quickening over time the country will have fewer options to deal with it, to raise money, to create strategies for plants that are slow-moving.
There are many uncertainties, and the requirements of iwi Ngāti Rangi for their taonga species will be crucial. What’s clear, though, is as the twin crises of climate change and biodiversity intensify, is under-performing native species will need all the help they can get.
Collecting seeds from threatened plants might become important, Deslippe says, so species can be re-planted upslope if needed.
“With the rate of warming and the rate of climate change in the park, we really have to take drastic measures to ensure our species will persist.
“That means potentially planting them in places where they currently don’t occur because by the time they’re seedlings and established plants, the climates will be about right for them, up-high.”
The situation evokes memories of John Cullen’s Tongariro, and spreading sacks of heather seed. This time, however, it’s native plant species being given the leg up to avoid areas where, for them, heather will have made their existence a living hell.