The arid alpine garden of Inland Marlborough

Forest and Bird, Volume 17, Issue 1, 1 February 1986, Page 22

The arid alpine garden of Inland Marlborough

by

Botany Division Regional Station DSIR, Nelson.

Peter Williams,

Hii between Christchurch and Wellington the plane passes directly over the highest point in New Zealand outside of the Southern Alps, the 2885 m Mt Tapuaenuku, on the Inland Kaikoura Range. To the east, in the valley of the Clarence, you can clearly see a geological fault line separating these mountains of shattered greywacke from the lower limestone hills forming the Chalk Range. As the land was uplifted during the Kaikoura Orogeny, the streams cut downwards forming chasms and gorges on the flanks of the main range. Many cut right through the limestone, polishing the hard layers of the walls to a pearly lustre. Calcareous rocks are a special feature of this area, for they are generally rare in the mountains of New Zealand. Before the limestone was deposited though, volcanic magma had extruded into the older greywacke as it accumulated. The highest peaks of the range are now criss-crossed with dykes of solid igneous rock, which weather to talus of a pinkish colour studded with large semipervious crystals.

Hottest and driest

These mountains thrust up into one of the hottest and driest regions of New Zealand. Blenheim, 60 km away, is the sunniest place in New Zealand, yet it receives only about 660 mm of rain per year, half that of Wellington for example. No wonder then a visitor would bake in the mountain gorges, but for the funneling of valley wind, the afternoon shade and the continual seepage of moisture from crannies in the rock walls. Yet in winter the gorges freeze solid for weeks. The low rainfall has an important effect during the winter too. Insufficient snow falls to build ice glaciers, despite the altitude, and the high slopes have only a relatively short period when they are blanketed with snow against the daily cycle of rock-shattering freeze and thaw. These conditions generate vast amounts of rock talus, with some chunks as big as houses, to accumulate as moving tongues of debris. These resemble the moraines of true glaciers, similar to those which must have formed these high basins during the Ice Ages.

A landscape transformed

The early colonial explorers of this land remarked on the absence of trees and we can probably attribute this in large measure to Polynesian burning. We know from breaking open surface rocks and measuring the thickness of the outside weathered layer or rind — just as on a mature cheese — that many lower slopes have been unvegetated for several hundred years.

However, one striking erosion feature of the inland Clarence has a more recent origin. Late last century Marlborough was smitten by a rabbit plague, aggravated by burning and overgrazing of the native tussock grasses. In the area now called ‘‘The Desert’, run-off stripped the bared topsoil completely and carved into the deeply weathered mudstone below. Kanuka has only slowly re-colonised, to form a sparse woodland. These are the most inland stands of tall trees in the Clarence valley. The only extensive areas of forest are in the north-east. Mountain beech is the main species, but there may be broadleaf, putaputaweta, lancewoods, coprosmas and other shrubs. Nearby, on limestone screes of the Chalk Range and as far south as the Branch river, are woodlands of Hall’s totara, which evoke thoughts of North American mountains. At higher altitudes, Hall's totara grows in gullies with mountain lacebark which produces masses of large white blossoms in the spring. Alas, the fires and introduced animals of the Europeans have pushed this beautiful mountain tree back into small relict pockets. Scattered individuals and dead trunks amongst the montane scrub, hint at a more glorious past. Perched on ledges and shady faces in the gorges, are more diverse forests of broadleaf, akiraho (Olearia paniculata), small-leaved kowhai, three finger, lancewood, and the rarer fierce lancewood. In these sites, and riverbeds where sheep and cattle are excluded, large bushes of pink broom (Notospartium carmichaeliae)

grow. In the Jordan valley at the northern end of the range there are groves of weeping broom (Chordospartium stevensonii) which has pendant sprays of pinkish, lavender flowers. These two are endemic to north-eastern South Island; but they are in the same family as the more familiar, introduced, yellow-flowered broom. Until recently these brooms all grew together along stream banks and bluffs over quite a wide area. However farm development and the scorched earth practice of weed spraying from helicopters has now forced the native brooms to back into these mountain strongholds.

Pride of Marlborough

The daisy family holds pride of place for species confined to north-eastern South Island. Most of them are seen in summer, spotting the bony landscape with yellow blooms. On the coast, or walking up a rocky gorge, you would first meet the shrubby Marlborough rock daisy (species of Pachystegia), with thick leathery leaves and large globular flowers of typical daisy form. On nearby stable bluffs or gravels you would come across masses of the low shrub Brachyglottis monroi with wavymargined leaves and covered in bright yellow flowers. Amongst the riverbed boulders could be low cryptic plants of Helichrysum depressum, looking deceptively like bits of stranded driftwood. Several other species of woody Helichrysum similarly have small leaves with glossy outer surfaces and hairy undersurfaces

pressed closely to the stem. The most widespread one is H. intermedium which appears as blackish patches on the bare cliff faces. H. coralloides is confined to Marlborough and resembles coral as the name suggests. Its grey-green branches are as thick as a little finger, and their very tips support bright yellow flower clusters, not unlike tiny sea anemones. Many other daisies are herbaceous. Ewartia sinclairii has a restricted geographical distribution, but its small, soft, grey-green leaves and masses of white flowers often festoon moist, shady banks. Raoulia cinerea is another plant endemic to the north-east, that has only recently been divested of its rare and endangered status because it was found to be more common than previously thought. One has to look in precisely the right sort of site to find it; creeping amongst sharp, angular gravel on flat ridges and spurs at high altitude. More widespread at high altitudes are cushions of Haastia pulvinaris, literally Haast’s cushion, but more commonly known as vegetable sheep. Their roots squeeze into nooks and crannies on the most inhospitable looking terrain, almost to the summit of Mt Tapuaenuku.

Climbing plants

Despite the great range of forms and habitats occupied by members of the daisy

family on the Inland Kaikoura Range, none of them are scramblers or climbers. This life form is nevertheless important in montane regions, perhaps because there are extensive areas of open ground or low shrublands dominated by matagouri (Discaria toumatou), coprosmas, cassinias and hebes, and snow totara (Podocarpus nivalis) at high altitudes. These provide the weak stemmed planted with a diversity of ‘climbing frames’. A few, however, seem less dependent on having support, and either form distinct mats or simply loll about on the landscape. Creeping poheuhue (Muehlenbeckia axillaris) binds almost any stony ground, but M. ephedroides is more choosey. This strange plant produces masses of fine, whippy, leafless, dark blue-green branches. that protrude vertically from coarse talus. Equally leafless at first glance, Clematis afoliata forms entanglements like springy balls of string. These hang from ledges or cliff faces quite unsupported other than by the mysterious, internal logic of the

clutching tendrils. These entanglements are yellow-green, and the whole mass can be covered with starshaped flowers of similar colour in early summer. Another species of leafy clematis also has similar coloured flowers, while a third has flowers of pale purple. The flowers of Parsonsia capsularis are particularly colourful in these inland regions. They soften the spiny matagouri with a loose net of lilac hue. The three species of lawyer (Rubus spp.) may also be colourful, both in flower and in their barbs, but these are a horror to the traveller off the beaten track.

Complex scree plants

When you do climb out of the gorges onto the open scree slopes, the effort will be rewarded with sights of some remarkable plants. Screes are habitats of temperature extremes, but they have one less obvious feature that makes plant life possible; beneath the coarse rocks of the scree surface are finer gravels and sands through which cool water percolates. Thus moisture does not limit plant growth, and neither do temperature or light on the frequent sunny days. Photosynthesis and transpiration can therefore proceed at near optimal rates. To ensure they absorb enough carbon dioxide from the atmosphere, many scree plants have thin-skinned and finely divided succulent leaves. Their resilience and trailing rhizomes and roots enables them almost to move with the mobile screes. Many are annuals or biennials, so that even as they are destroyed over winter, seeds cast in the autumn lie poised to renew the populations come summer's warmth. Many scree plants are found throughout eastern South Island, but several are special to the Kaikoura region. The handsome Epilobium forbesii, for example, sprinkles the fine grained screes with low rosettes of downwardly curved glandular leaves. These glistening clumps support pink flower buds that turn white as they open out to a full 1 cm diameter. Large flowers, up to 2 cm diameter, are sported by one of our two native species of convolvulus (C. fracto-saxosa), literally the one that grows in broken rocks. The flowers are a small version of the "‘granny pops-out-of-bed" we played with on the way home from school. But there the similarity ends. Rather than bright green the leaves of the rock convolvulus, covered in soft, greyish hairs, match their surroundings. The cryptic colour of these plants makes them difficult for us to see, but it does not deter the large alpine grass-hoppers, that leap and tumble about the screes, from feasting on the succulent leaves.

Large reserves needed

These fascinating natural features and biota can all be found within the Tapuaenuku Ecological District, of which the Inland Kaikoura Range forms the high core. This land is nearly all Crown Lease and only one Scenic Reserve exists within this district, or indeed within the whole catchment of the Clarence River (Timmins and King 1984). This strangely irregular shaped reserve was gazetted in 1962 in recognition of the landscape values of the high

peaks. The biota are just as important to conserve, but reserves will have to be large, and cover a full altitudinal sequence. Ideally, they should link features such as the Hodder Gorge and Winterton Basin in the west with the Hall’s totara forests and kanuka stands in the east. Then there should be corridors across the Clarence to similar large reserves on the western slopes of the Seaward Kaikoura Range — an area yet to be botanically surveyed.

It takes some effort to fully appreciate these landscapes and their inhabitants. Firstly, you have to make your way from the coastal State Highway | up the long dusty inter-montane valleys, to the lower reaches of the tributaries. Here you will have to take to the riverbed on foot, and be prepared for many crossings. But when you've experienced this remote, wild country, you will be able to share the sentiments of the early geologist McKay, when he reported on the Inland Clarence as: "... impressing the explorer with the massive solidity and giant proportions of the great cliffs rising from the deepest part of the gorge. Yet high above in the sky these terminate in clear-cut pyramidal peaks, gables and roofs, massive below, light and airy above. Architectural in aspect, these vertical walls and steep slopes, bearing just a due proportion of flowering plants and gorgeous shrubs, may be seen and admired, but are not easily described; and when a peep of sky dropping west from the zenith is seen, filled by the glistening snows and jagged summits of Tapuaenuku, art may strive in vain to copy the beauty, the grandeur, and the majesty of the picture." g& This article first appeared in the NZ Alpine Club Journal (1985)