From: Nature in Eurobodalla 7 (1992); pp 65-69. [published 29 Oct. 1993]
A VEGETATION MAP OF MONTAGU ISLAND, 1990.Petrus C. Heyligers
Today, the general aspect of the vegetation on Montagu Island is determined by a small number of tough herbaceous plants. The trees and shrubs that were present when the lighthouse was built disappeared during the first few decades of lighthouse operation. Unfortunately, there are no reports on what species were present, nor on what they were used for. Grazing by rabbits and livestock, especially goats, not only prevented regeneration, but also influenced the composition of the vegetation that remained. Moreover, other species were introduced, either intentionally, for instance for lawns and gardens, or by accident, such as with fodder for the horses.
The floristic inventory of the island, published in Nature in Eurobodalla no. 2, 1989, included a short description of the vegetation. The purpose of the present article is to present a map of this vegetation, together with a descriptive legend. It records the distribution of the vegetation at the time the responsibility for the island was transferred from the Commonwealth of Australia to the State of New South Wales.
Users of this map must bear in mind that boundaries on vegetation maps are seldom sharp in nature. This is particularly well illustrated on Montagu Island, where differences in vegetational cover are often determined by a proportional change in co-dominance rather than by the juxtaposition of areas characterized by different species. The vegetation types have been named after their most common species and indicated on the map by the first letter of these names (Figure 1).
2. Mat-rush - Bracken vegetation (MB). This is a mixed vegetation of Mat-rush and Bracken, with Mat-rush often the more common of the two. The vegetation is generally dense. Apart from Milk-vine, other species present could include Scrub Nettle Urtica ncisa.
3. Bracken vegetation (B). Bracken is dominant; Mat-rush is absent or present in small numbers only. This vegetation is usually a dense tangle of bracken fronds and twiners such as Stephania Stephania japonica var. discolor.
4. Mat-rush - Tussock Grass vegetation (MT or mt). This type resembles Mat-rush vegetation, but is recognized by the scattered occurrence of Blue Tussock Grass Poa poiformis. As with Mat-rush vegetation, a denser (MT) and a more open aspect (mt) have been distinguished.
5. Tussock Grass - Mat-rush vegetation (TM). Tussock Grass, together with Mat-rush and, to a lesser extent, Knotted Club-rush Isolepis nodosa and Scrub Nettle, characterize the vegetation between bands of rock, cropping out at a shallow angle on North Island.
6. Mixed Grasses vegetation (G). This is a floristically mixed community on shallow soil, restricted to higher parts of the islands. Various grasses, for instance Kangaroo Grass Themeda triandra, Paddock Love-grass Eragrostis leptostachya, Blady Grass Imperata cylindrica, Blue Tussock Grass, and Prickly Couch Zoysia macrantha, together with Bracken, Mat-rush and Club-rush, occur in varying proportions. Creepers and twiners such as Scurvy Weed, Milk-vine and Stephania may be present, too. Generally, the vegetation is much shorter and less dense than that of the previous types.
7. Prickly Couch - Tussock Grass vegetation (PT). Prickly Couch, sometimes together with Salt Couch Sporobolus virginicus, characterize the low-lying southern end of South Island, the area where saltspray is most intense. Mixed in are patches of low Tussock Grass, some Club-rush and scattered New Zealand Spinach Tetragonia tetragonioides. Angled Lobelia Lobelia alata and Kidney Weed Dichondra repens occur among the couch vegetation; Annual Beardgrass Polypogon monspeliensis may be found in more open spots. The vegetation is low, rather carpet-like and is interspersed with many small rocky outcrops.
8. Kikuyu vegetation (K). Kikuyu Grass Pennisetum clandestinum is a dominant element in the vegetation on the western side of South Island and occurs as scattered patches elsewhere. It forms a dense, thick sward of intertwining runners which smothers other plants such as Mat-rush, Bracken, and Common Reed Phragmites australis, which originally occupied such sites. Kikuyu Grass was introduced to the Tilba district in the 1920s (N. Hoyer, pers. comm.), but the date of its arrival on Montagu Island is unknown.
Round the rock dome in the centre of South Island Buffalo Grass Stenotaphrum secundatum is often associated with Kikuyu Grass, or may even be predominant. It was introduced in 1916 as a lawn grass for the lighthouse area (M. Higgens, pers. comm.), where it still fulfils that function.
9. Rambling Dock - Ink Weed vegetation (Rl). In this type a few areas have been brought together dominated by species which take hold after severe disturbance of the existing vegetation. It has been named after two of the most prevalent of such species, viz. Rambling Dock Acetosa sagittata and Ink Weed Phytolacca octandra. Other species found in such areas include Scurvy Weed, Stinging Nettle, Blady Grass, and Black-berry Nightshade Solanum nigrum, as well as twiners, especially Stephania.
Common Reed.
The distribution of Reed presents an as yet unsolved ecological puzzle. Normally associated with swamps or at least high groundwater tables, Reed seems to defy this rule on Montagu Island as it grows round some of the rock outcrops on the highest parts of both islands. However, it never forms pure stands, but occurs mixed with other species, usually Mat-rush, Bracken, and Scrub Nettle; twiners, especially Stephania or Cape Ivy Delairea odorata, tend to be common, too. On the vegetation map the distribution of Reed has been indicated by dots.
Other Vegetation Types.
Margins of high cliffs have a characteristic band of Prickly Spear-grass Stipa stipoides, and ledges inaccessible to goats provide a refuge for shrubs such as Coast Rosemary Westringia fruticosa and White Correa Correa alba. Crevices in rocks may provide a foothold for Rock Fern Cheilanthes austrotenuifolia, Shore Spleenwort Asplenium obtusatum, or Australian Stonecrop Crassula sieberana. More eye-catching however, are the orange, yellow, grey and glaucous lichens, which on sea-facing rocks appear in a zonation reflecting the diminishing effect of salt spray.
Beaches are small and limited to somewhat protected situations. They are usually formed of small boulders or pebbles, occasionally of shell grit, and are home to New Zealand Spinach, European Sea-rocket Cakile maritima, Sea Spurge Euphorbia paralias and various species of Chenopodiaceae. Rock hollows filled with rainwater and areas influenced by groundwater seepage have different plant assemblages again. Unfortunately, interesting as these plant communities are, they are too small to be represented on a vegetation map at the scale presented here.
Acknowledgements.
Aerial photographs taken on 29 September 1988 by the NSW National Parks and Wildlife Service were kindly made available to us by the Narooma office of the Service. I also would like to express my appreciation for their permission to carry out the fieldwork for the vegetation map.
Petrus C. Heyligers, 3/2 Sexton Street, Cook, ACT 2614; 4 August 1993.
[A coloured version of the map prepared by Petrus Heyligers in 1990 representing the vegetation pattern on the island before any replanting and restoration work had occurred. Following this survey Kikuyu grass Pennisetum clandestinum continued to spread eastwards on South Island and became much more firmly established on North Island.]
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