MONTAGUE ISLAND'S ENVIRONMENT, GEOLOGY & FLORA

Montague is certainly a unique environment through being a large, offshore island, rising up from the deep sea bed and surrounded by or in close proximity to the East Australian Current, and only 5 nautical miles from the continental shelf.

Montague Island is roughly rectangular, 1.4km long and 525 metres wide at its widest, and is oriented north-south. A ravine divides it into a northern section, covering approximately one third the total area, and a larger southern section on which the lighthouse and other developments are located. The two sections are commonly referred to as the north and south "islands".

The landscape rises spectacularly from the ocean, with the grey-brown south end rocks contrasting with the black rocks of the north end. A bright orange lichen covering rings the island on the rocks above the spray line, and the low vegetation highlights the white of the lightstation buildings with the tower overlooking all.

GEOLOGY

The island is part of the Cretaceous Mount Dromedary Igneous Complex. The southern section consists of banatite, an intrusive coarse grained granitic rock. The northern section is composed of an older volcanic complex consisting of andesitic lava and tuffs, similar to basalt.
The southern section of the island has many rock outcrops (tors) and reaches a height of 64 metres above sea level. The northern section is slightly lower with fewer rock outcrops.
The coastline is generally rugged with steep cliffs, especially around the northern section. A few small bays have sandy "beaches" of only a few metres width at low tide.
Much of the island is covered by remnant sand dunes up to 1m thick. The soils formed on the dunes are generally thin.
Swampy areas occur on the slopes, particularly near the southern end.
During the last ice age, when sea levels were 120 metres lower, the island would have been a hill inland about 7 kilometres from the sea. Around 8500 years ago rising seas severed the island from the mainland when the present coastline was approximately formed.

FLORA

Photographic records show that at the turn of the century much of the southern section of the island was covered by scattered small trees and shrubs, which probably included banksias, acacias and casuarinas. No native trees and few shrubs remain today. The loss of trees has probably resulted from burning for firewood by the lightkeepers and grazing by rabbits and goats.
More than 160 plant species have been recorded in various studies over the years, of which nearly half were introduced species, whether by humans or by natural occurences such as birds or winds. A number of species recorded earlier have not been seen in later studies.
The native plant species demonstrate the islands previous connection to the mainland.

The dominant vegetation is matrush (Lomandra longifolia) which thickly covers the ground over much of the island. Blady grass (Imperata cylindrica), bracken (Pteridium esculentum) and tussock grass (Poa labillardiera) commonly occur with the matrush and are sometimes locally dominant. Tussock grass is extensive on the slopes of the north island. A few shrubs including Westringia fruticosa, Pelargonium australe, Melaleuca armillaris and Correa alba occur in sheltered places and on cliff edges where they were safe from grazing by rabbits and (formerly) goats.
One species of Acacia the Coastla Wattle (Acacia Sophorae) is found in patches around the island.
Wetter areas support reed (Phragmites australis) and the rushes Juncus sp. and Scirpus nodosus. Ferns occur in some moist sheltered places below cliffs. A variety of herbs and ground covers also occur.

INTRODUCED FLORA

Open grassy areas, predominantly kikuyu (Peniosetum clandestinum) and some buffalo grass (Stenotaphrum secundatum), both introduced species, have replaced native vegetation around the buildings and along tracks, and Kikuyu has now dominated much of the western side of the island. This has caused a problem for the island's Little Penguins and rectifying this has become the focus of much of the conservation programs on the island. Download the Shorebird Habitat Improvement Program pdf Case Study for details.

The other main species of concern is rambling dock (Acetosa sagittaria) which displaces native plants. It occurs in large patches on the south island.

Other introduced species occur in small numbers, mainly along tracks and drainage lines from the residences and in the former garden area.