Amongst the vast lexicon of terms for geological features and rock types, ‘serpentine’ stands out as one of the best adjectives on offer. Quite apart from any linguistic appeal, the processes associated with the formation of serpentine rock are especially interesting. Distinctive plants also develop in association with the unusual soils and substrates from places where serpentine is important as a base rock, meaning that (unsurprisingly) such places are like catnip to me.
Cole and Trent also didn’t need to be asked twice to go wandering in the Red Hills after a work trip to Nelson last year. Spanning the boundary between Nelson and Marlborough, this impressive landscape is part of a discontinuous spine of ultramafic areas running from North Cape down to Southland. ‘Ultramafic’ and ‘serpentine’ environments are frequently discussed in a synonymous manner, and the simple explanation for what makes these places tick is that the soil is generally low in nutrients whilst possessing high concentrations of toxic metals.
In essence, the business of existence is particularly challenging on ultramafic substrates, and as a result, distinct species and strange vegetation patterns have evolved in response to these highly unpromising soil environments. Intriguingly, many species (such as Astelia aff. graminea, pictured above) exhibit mineral or metallic tones in their foliage – not unlike the rocks and soil surrounding them.
The reason for Red Hills’ name is self-evident when one looks at the rocks in the image above – which look like they belong more to Australia than to the upper South Island. Aside from the relative intensity of their colour, the underlying geology is unusually conspicuous (when compared with other environments) due to the sparse vegetation cover that develops on these toxic substrates.
The openness of the tussock cover at Red Hills (where a distinctive species closely related to red tussock, Chionochloa defracta, has evolved) provides a matrix in which interesting characters like the nationally endangered, endemic forget-me-not, Myosotis laeta, and a blood red, dwarf sedge, Carex uncifolia, find opportunities for growth on bare ground.
On an outcrop near the top of the hill leading to the plateau, it appeared that the nature of the substrate was markedly different over a small area – demonstrated most conspicuously by the fact that large specimens of native beech had the temerity to achieve some sense of scale on this boulder-strewn outcrop.
The low, mounding shrub pictured above, left (called Coprosma fowerakeri) was of particular interest to me, having never seen it in the wild before. On the slope below this intriguing outcrop, the Red Hills hebe (now classified as Veronica baylyi, and formerly known as Hebe carnosula) registered as attractive glaucous mounds amidst the tussockland – forming a simple matrix of greyish-green and tawny tones (as pictured above, right).
The sequence of environments through which one moves on the walk from beech forest within Wairau Valley (in which mistletoes endure), through to shrubland, ultramfic tussockland and the tarns on the plateau (one of which is shown below), make this a particularly interesting part of the country.
One final note concerns a plant that is not endemic to ultramafic habitats, but has an unusual life cycle. With its coral-like stems, Exocarpus bidwillii already stands out as an oddity within its surroundings; an impression only enhanced by the knowledge that this hemi-parasitic shrub is hitching a ride off its near-neighbours.