Helen McKerralNZ’s geothermal vegetation

During our recent holiday on New Zealand’s North Island, we saw ecosystems that were so different to South Australia’s landscapes that they seemed positively alien. The apparent darkness of a glow worm cave gradually brightening to become a miniature replica of the Milky Way was memorable… but nothing was more eerie than the geothermal areas we visited.

Rugged up against the rain

Craters of the Moon

In part, this was because it bucketed with rain the entire time, so the surrounding landscape was shrouded, with the steam contrasting strangely against the mist and cold. At both Craters of the Moon and Wairakei Thermal Valley, the four of us were the only ones crazy enough to brave the weather, but this meant there was no distraction or noise from other visitors. It would have been no surprise to see a dinosaur lumbering out of the fog, or some strange sci-fi creature swooping overhead, as if we were on another planet.

Alkaline pool

Here’s a great introduction to NZ’s geothermal fields. Systems may be alkaline (alkaline chloride systems), characterised by very clear water that’s risen slowly from deep in the ground; and we saw such a pool in the forest above Rotorua. Acid sulphate features, such as Craters of the Moon, occur when the water is trapped for a time below ground so that additional gases dissolve into the water.

Mineralisation and associated mosses and algae

Temperatures can range from tepid to 97°C within a few centimetres of the soil surface, and there can be toxic levels of minerals concentrated and deposited around outlets. These extremes of heat, pH and concentrated minerals, caused the evolution of “extremophile” microorganisms that thrive around geothermal areas, offering intriguing insights to the potential for life on other planets, and for use in mining, chemical spill recovery, medicines, and more.

Clubmoss

The plants are similarly amazing. Though no vegetation survives steamy ground reaching 97ºC, mosses, algae and lichens can manage ground temperatures of 70ºC. Hence, in the frost-free, constantly warm microclimate, it’s possible to find tropical species such as clubmoss (Lycopodium cernuum), and ferns such as Nephrolepis flexuosa and Dicranopteris linearis var linearis. For species occurring elsewhere in the world, the geothermal areas of New Zealand’s north isle comprise the southernmost extent of their distribution.

Geysers at Rotorua

Just as with the caves, New Zealand’s geothermal springs come in a range of tourist options, from the large-scale packaged conveyor-belt tours to the smaller, quirkier options. We viewed the famous geysers at Rotorua from the adjacent forest and had no inclination for a closer look, but the Wairakei Thermal Valley was perfectly to our taste, despite disparaging online reviews.

The campground was up a dirt road and populated with just a couple other guests… as well as ducks, chickens (and chicks), guinea fowl, a llama, peafowl, a cat and a miniature piglet. Unsurprisingly, the owner was pleasantly eccentric!

Fruiting lichen

Like many geothermal sites, Wairakei has been severely degraded by the introduction of geothermal electricity turbines just downstream: the site lost all seventy of its geysers and at least another 170 alkaline springs. Sadly, even tiny changes in water quantity, quality or temperature can have devastating effects on the local ecosystems, and the extraction of geothermal energy has caused numerous geothermal surface features throughout New Zealand to vanish completely ; as recently as 2005 there was no explicit protection for even sites as famous as Rotorua. At Wairakei, old black-and-white-images on the kiosk walls showed towering plumes of steam and water billowing skywards but that was long ago and, after being handed an electronic temperature gauge, we headed off in the pouring rain, wondering whether we’d see anything at all.

Yes, the place was run down – wear waterproof boots and be ready for mud if you head out in the wet – but it was also wonderful in that there were no barrier fences, no guides telling us what not to do, and no crowds. We respected the vegetation, of course, and didn’t recklessly trample across delicate plants, but the freedom was refreshing.

Some kind of strange moss

Within every geothermal field, the range of temperature, moisture and soil mineralisation creates a range of different vegetation communities, which is fascinating for anyone interested in plants because the changes are so many and varied, and occur over such small –often tiny – distances (see NZ Geothermal Vegetation Dynamics). At Wairakei, we walked along ferny creeks, saw strange microorganisms growing on the mineral deposits beside fumeroles, mosses beside bubbling mud pools and just too many other plants to list.

Craters of the Moon

Craters of the Moon is aptly named, and better maintained (by volunteers) than Wairakei, with extensive, wide boardwalks suitable for wheelchairs. Once again we were the only crazy visitors in that weather, and we set off with the surrounding pine forest hidden by mist and rain. Clearly, there was little point in climbing to the lookouts on the higher land around the circumference, so we completed a full circuit of the low-lying plain instead.

Prostrate kanuka at Craters of the Moon

The most obvious vegetation at Craters of the Moon is a fascinating endemic plant: prostrate kānuka (Kunzea ericoides var. microflorum), which grows only in geothermal areas. The hotter the ground temperature (up to 55ºC!), the more prostrate the plant. As well, we saw numerous lichens and liverworts of almost every size and colour – utterly fascinating, and my companions left me behind as I crouched with my jacket over my happy snappy camera to photograph yet another tiny strange plant form.

Ferns around a fumerole

Even though these particular plants are not ones any of us Aussies will ever grow in our gardens, their sheer adaptability took my breath away – sometimes literally near the more sulphurous fumeroles! – and I guarantee that anyone who is interested in plants will be utterly captivated by the geothermal fields of New Zealand’s north isle.

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Helen McKerral

About Helen McKerral

Horticultural journalist, photographer, contributor to many garden magazines, and author of 'Gardening on a Shoestring'. Adelaide Hills, South Australia

3 thoughts on “NZ’s geothermal vegetation

  1. anne latreille on said:

    Fascinating Helen! I’ll be printing it out so that I can see it when next we go to NZ. A good reason to do the North Island instead of the South.

  2. helen mckerral on said:

    Anne, you’ll love it. Don’t miss the Taranaki district for gardens (see my other NZ posts). THe coromandel Peninsula is stunning too. Re north Island vs south, lots of people have told me it’s best to see the north isle first because “the North island is pretty, but the south island is spectacular”.

  3. James Beattie on said:

    Helen, what a wonderful post! The ecology of plants that are able to grow in marginal and challenging ecosystems always grab my attention. Your pictures are just the ticket.
    Talking about the Taranaki region, I have been a big fan of Abbie Jury’s blog for a few years now. Her and her partner’s garden is in Waitara, which is in the same area if I’m not mistaken, looks beautiful and chock-full of a wonderfully eclectic range of plants. I’d love to visit their garden in the near future.

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