AN UNUSUAL PLANT COMMUNITY ON SOME SOUTH WESTLAND PIEDMONT MORAINES. by G. Rennison* and J.L. Brockf

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1 223 AN UNUSUAL PLANT COMMUNITY ON SOME SOUTH WESTLAND PIEDMONT MORAINES by G. Rennison* and J.L. Brockf In South Westland there is an extensive area of piedmont moraines lying between the sea and the western scarp of the Southern Alps, and bounded by the Waiho River to the north and the Cook River to the south (Fig. 1). In the main the existing vegetation is podocarp-broadleaf forest, but with small pockets of a plant community which has definite alpine affinities. From the air these show up as light-coloured areas against the dark forest, and occupy areas of infertile terrace. For an explanation of their occurrence an outline of the recent geological history is pertinent. Late Pleistocene History of the Moraines Approximately two thirds of the moraines are mapped as Okarito Formation and the rest as Moana Formation (Warren, 1967; Fig. 2). Both were formed during the advance of the Otira Glaciation, the Okarito Formation being correlated with the Kumara-2 and early Kumara-3 advance, and the Moana Formation with the later Kumara-3 advance (Suggate, 1965). The Okarito Formation may also include remnants of moraines formed by the earlier Waimea Glaciation. From radio-carbon dating, Suggate suggests that the early Kumara-3 advance commenced approximately 16,000 years before present (BP). The late Kumara-3 advance commenced approximately 1,500 years later (14,500 BP) and resulted in the Fox and Franz Josef Glaciers being extended beyond the present coastline, with an extensive lateral moraine complex being formed along the periphery of the Okarito Formation. Vegetation Development on the Moraines The following is an outline of the possible mode of vegetation development on these piedmont moraines: 1. Following the retreat of the ice after the early Kumara-3 advance (16,000 BP), vegetation invaded the moraines and the soils were quickly impoverished on poorly drained sites. Leaching may have taken place under colder climates than at present, or during interglacial periods which precluded full development of forest (Wardle, pers. comm.). 2. The later Kumara-3 advance caused the Fox Glacier to overwhelm areas of the older moraines with ice, and the prevailing Ice Age climate maintained the current vegetation on undisturbed surfaces. 3. Following the Kumara-3 advance, a warming climate (14,000 BP) caused a rapid glacial retreat and forests similar to present day forests invaded both the newly formed moraine deposits and the older areas. However, the forests were unable to occupy areas where the greatest impoverishment of the soil had occurred, and the cold-climate community survived and persists to the present day. *(Senior Ranger), Westland National Park, P.O. Box 38, Fox Glacier. t(scientist), Grasslands Division, DSIR, Private Bag, Palmerston North.

2 224 Present-Day Vegetation (a) Skiffington Swamp/Lake Gault Area (Figs. 3,5,6). The most accessible area of this community is on an Okarito surface located on the isthmus between Lake Gault and Skiffington Swamp, north-east of Lake Matheson, and near the Fox Glacier township. Unfortunately part of this community has undergone recent modification by man. Firstly, in the early 1930's, fire burnt part of the shrubland, which has been replaced by red tussock-dominated grassland. Secondly, Skiffington Swamp was raised by the construction of an earth dam across the natural outlet to Lake Gault in 1958, to increase its water storage capacity for a hydro-electric generator providing power for the Fox Glacier township. Several gorse plants have established themselves on the dam but as only one was seeding (it has since been eradicated) control will be easy. This plant must have been brought in as seed on the bulldozer used to construct the dam. At the same time the bulldozer (for reasons known only to the driver) bladed out swathes of topsoil at random over part of the area. Plant recovery and growth is so slow on these impoverished soils that the cleat marks of the bulldozer tracks are still visible, and the bladed areas are now rectangular tarns.

3 225 Fig. 2: Geological map of the area between Waiho River and Cook River, South Westland. The area consists of gently sloping to flat grasslands or low Calarophus Gleichenia swards separated from each other by low shrub stands along water courses and on low ridges. Small natural tarns and pools (1.5 x 0.5 m av) are common over the flatter areas. The community was analysed and classified using the point-intersect method developed by Atkinson (1962). The vegetation can be divided into three types: 1. Chionochloa rubra - Calarophus sedge tussock-land with silver pine: found around the outflow from Skiffington Swamp towards the lake (Fig. 3). 2. Gleichenia - Calarophus sedge fernland with pygmy pine: found on the only ridge from which the original shrub layer had been burnt off. 3. Calarophus Gleichenia fern-sedge-land with red tussock: covers the rest of the area fairly uniformly. Of the 34 species comprising the community (Table 1), 4 are found on piedmont moraine only, 17 in piedmont moraine, sub-alpine and alpine communities; 8 in both lowland and alpine communities; and 5 restricted entirely to the lowlands. From this the strong affinities of this community with alpine and sub-alpine communities is apparent, and the inability of lowland forest species to invade is demonstrated. Wardle, in a report to the Westland National Park Board (1965), suggests that this type of community represents the ultimate development of vegetation on Ice Age gravels.

4 Fig. 3: Vegetation of the Skiffington Sawmp/Lake Gault area. Four soil pits were dug and their profiles examined (Fig 4); in each case there was a dense, spongy, peaty root mat, overlying a gleyed heavy clay. It is not known whether the gley-podzols on these old moraines were produced under an earlier forest canopy or whether, as Wardle (pers. comm.) suggests, they were produced at a time of colder climate when conditions for forest growth were unfavourable. (b) Gillespies Road Area A similar though wetter site in the middle of the Moana moraine area to the south, which is readily accessible from the road to Gillespies Beach, was also investigated.

5 227 Topographically the area is a shallow, saucer-like depression which appears to have been an ephemeral lake or an old kettle-hole (Wardle, pers. comm.). Differing types of vegetation arranged in concentric rings surround an open central area, and can be described as follows (Table 2): (1) Rimu miro forest with a poorly developed, sparse shrub layer. (2) Rimu toatoa forest with totara, mountain cedar and a heavy shrub layer. (3) Manuka/silver pine forest with a lower layer of toatoa, Myrsine divaricata, mountain cedar, silver pine, totara and manuka. (4) Manuka/silver pine scrub with some bog pine and Gahnia rigida; (5) An open central area of Cladium-Leptospermum-Calarophus sedgeland with Carex coriacea (Atkinson, 1962). Drainage of this area is poor but not entirely lacking, as a sluggish stream carries a continuous flow of water away into the forest. PROFILE (J) Under Calaronhus-Glelchania sward.(5-6* slops) 1-1-5" Dense peaty root mat. Cj.. Light gray gleyed silty clay with soma Iron deposition along lower boundary. sharp contact) disuse contact) 12*" 8" 6»" Light green-grey silty clay. No root channels. l-1o Brown root mat. g Brown highly or game clayey mud. Much root penetration and water movement through layer. 6" Grey -brown silty clay. Grey-green silty clay. Few root channels Yellow-brown clay with much iron. Gleyed silt.

6 228 A comparison of the two areas (Table 3) Although several species are shared between the two communities the proportions are substantially different; physiognomically and structurally they are unrelated. Their future development also appears to be different, as the Skiffington Swamp/Lake Gault area seems to be stable on a slowly deteriorating gley-podzol, while the Gillespies Road area seems to be moving in the classic Westland swamp sequence through manuka/silver pine shrubland to rimu forest, on steadily deepening peat. ACKNOWLEDGEMENTS Dr P. Wardle, Botany Division, D.S.I.R., Lincoln, for information and discussion concerning the area, and Mr B. Maunder, Botany Department, Canterbury University, Christchurch for soil profile descriptions. REFERENCES Atkinson, I.A.E. 1962: Semi-quantitative measurements of canopy composition as a basis for mapping vegetation. Proc, N.Z. Ecol. Soc. 9. Stevens, P. 1962: Soils of the Waiho Valley. Ph.D. Thesis held at Westland National Park H.Q. Suggate, P. 1965: Late Pleistocene Geology of the northern part of the South Island, New Zealand. N.Z. Geol. Survey Bulletin 77. Wardle, P. 1965: Unpublished report to the Westland National Park Board. Wardle, P. 1972: Unpublished provisional list of vascular plants from Westland National Park and neighbouring lowland and coastal areas. Warren G. 1967: Sheet 17 Hokitika (1st. Ed.) "Geological map of New Zealand 1:250,000" D.S.I.R., Wellington, N.Z.

7 Fig. 6: Calorophus - Gleichenea fern sedge land. (Area 3, Fig. 3.)

8 230 Table 1: Species of vascular plants found (a) on the Skiffington Swamp/Lake Gult Isthmus, and (b) from the peripheral shrubland. Species Distribution * (a) Lycopodium fastigiatum L A Lycopodium ramulosum P A Gleichenia microphylla L Dacrydium bidwillii L A Dacrydium biforme P A Dacrydium colensoi 1 A Dacrydium laxifolium P A Dacrydium laxifolium x intermedium P Libocedrus bidwillii L A Celmisia graminifolia P A Coprosma colensoi P A Coprosma brunnea L A Cyathodes empetrifolia P Dracophyllum longifolium P A Dracophyllum palustre P Dracophyllum traversii P A Donatio novae-zelandiae P A Drosera spathulata L A Gaultheria depressa P A Gentiana patula P A Haloragis (pakihi species) 1 Nertera scapanoides 1. Olearia lacunosa P A Pittosporum crassicaule P A Calarophus minor P A Carpha alpina P A Chionocloa conspicua P A Chionocloa rubra P Cladium glomeratum L Gahnia rigida L Gaimardia ciliata P A Notodanthonia setifolia L A Oreobolus strict us P A Thelymitra venosa P A (b) Dacrydium bidwilli Dacrydium biforme Dacrydium colensoi Dacrydium intermedium Dacrydium laxifolium Dacrydium laxifolium x Libocedrus bidwillii Phyllocladus alpinus *L = Lowland, P = Piedmont, A distribution only. intermedium Alpine, all based on local Podocarpus acutifolius Coprosma parviflora Dracophyllum longifolium Eleocarpus hookerianus Leptospermum scoparium Pittosporum crassicaule Pseudopanax crassifolium Pseudopanax simplex

9 231 Table 2: Species of vascular plants found in Gillespies Road community - species of (a) open sedgeland, and (b) peripheral shrubland. (a) Dacrydium bidwillii Dacrydium laxifolium Celmisia graminifolia Leptospermum scoparium Dracophyllum palustre Calarophus minor Carex coriacea Cladium glomeratum Gahnia rigida Oreobolus strictus (b) Dacrydium bidwillii Dacrydium biforme Dacrydium colensoi Libocedrus bidwillii Phyllocladus alpinus Podocarpus acutifolius Coprosma parviflora Leptospermum scoparium Myrsine divaricata Pseudopanax crassifolium Table 3: Abundance of species shared between the Skiffington Swamp/Lake Gault Isthmus and Gillespies Rd. communities as a percentage of canopy cover. Species Isthmus Gillespies Rd. Leptospermum scoparium 1 14 Calarophus minor Cladium glomeratum 1 16 Dracophyllum palustre 8 4 Dacrydium colensoi 4 1 Dacrydium laxifolium 1 1 Celmisia graminifolia I Oreobolus strictus \ <1 <1 Gahnia rigida

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