Interpretive panels introduce the alpine vegetation around a tarn.
0.5km over Lewis Pass summit (907m) on the Hanmer side is the St James Carpark. The start of the track is clearly signposted.
From the carpark follow signs past the tarn to a well-formed loop. The boardwalk sections are there to protect the fragile alpine vegetation.
The plants brave enough to venture into the alpine world are rewarded with a stunning home, but have to cope with an environment that is harsh in the extreme. Avalanches are common, wind bombs, floods, landslips, droughts and tumbling boulders create a desolation to the landscape. But plants still survive. Other areas above the tree line have high winds, extreme cold and submersion in snow, searing summer heat, torrential rain and periodic disturbance of the soil to contend with. To survive in their niches, they have developed cunning and ingenious ploys.
Snow tussocks thwart the wind by weaving a dense mat of interlaced stems, trapping a warm layer of air near the ground. They hibernate in winter, conserving moisture and nutrients.
To withstand the environmental extremes, other plants have a hairy leaf and stem known as a tomentum, a fine hair like peach fur which insulates them from the desiccating effect of wind. Some alpine plants also have chemicals and salts in their held moisture, which act as a type of anti-freeze, inhibiting the expansion of freezing internal water, which would result in tissue damage. To keep grounded in moving scree slopes, many plants send out snaking underground stems, with tap roots penetrating deep into the soil like an anchor. During winter these perennials also die off, only to re-emerge the following spring and spread like a mat. This has the effect of binding the unconsolidated rocks allowing a seed bed for tussocks and other plants, thus stabilising the slopes for colonisation.
A feature of note displayed by New Zealand’s alpine plants is that 93% of them are endemic to the New Zealand landmass, compared to 80% of the vascular plants in general. This high degree of endemism is usually associated with a long history of evolution, but it is generally agreed alpine conditions have only been in existence in New Zealand for 2 million years. The most likely explanation is that a rapid evolution has occurred.
Another curious feature of the alpine flora is its split in distribution, for example some plants are only found in Nelson and Fiordland and absent from the intervening regions. The best guess here is that during the last ice ages an extensive ice sheet covered the entire central region, splitting the island with an uninhabitable nival zone. The plants have not yet re-invaded the gap.
Unlike other counterparts in Europe, many New Zealand alpine flowers are lacking in colour, white and yellow being the preferred palettes. The lack of specialised pollinating insects probably contributes to this, with long-tongued bees and butterflies being the most attracted to colour, and both being scarce in our insect inventory.
As you walk up from the treeline, the alpine vegetation traverses differing zones, from mixed snow-tussock scrub with a variety of tall snow tussocks, shrubs and large herbs. The herbfields are characterised by taller Celmisia, Ranunculus and Aciphylla species. On flatter ground, bogs are common in hollows and depressions, matted in a soft turf and mottled with small tarns and lakelets.
In the higher alpine zones are fellfields and scree communities, where plants occupy scant soils or exploit moisture in crevices. Cushion plants such as rock sheep (Raoulia) lie low to the ground and take advantage of the warmer layers with greater shelter from the wind.
Identification of individual alpine species takes decades of meticulous study, however learning the main families can be accomplished relatively easily with a curious mind and a little research. The main genera are as follows:
Ranunculus or buttercups – include Ranunculus lyallii, the largest buttercup in the world.
Anisotome – a relative of the carrot family and with similar leaf forms.
Aciphylla – forty alpine species distinguished by their sharp leaves (a direct translation of their botanical name). Also known as speargrass or Spaniard.
Dracophyllum – Prone to hybridise, the most commonly encountered are D. menziesii, with its pineapple-like leaf head, D. uniflorum and D. longifolium.
Celmisia – One of the most important alpine geneera with over 50 representatives. Often called mountain daisies, look for C. ramulosa, C. bonplandii, C. petriei and C traversii.
Raoulia – cushion and mat plants sometimes with a spongy texture and a mosaic-like appearance.
Gentianella – the southern hemisphere version of the much loved European gentians, with similar delicate flowers.
Ourisia – only found in South America, Tasmania and New Zealand. Often found with white 5-lobed leaves.
Interestingly this is one of only a handful of locations where all five species of southern beeches co-habit.
South Island ▷ Canterbury ▷ Hanmer Springs
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