Plants and wildflowers of Rottnest Island
Prior to separation from the mainland, Rottnest Island would have had the same range of plants found today on the adjacent mainland, where about 1,500 native species flourish.
The sea level rose above present levels on two occasions, about 5,500 and 2,500 years ago. As a result, Rottnest was partly submerged and became 11 small islands. Exposure to salt and wind eliminated hundreds of species at that time so that today there are only about 140 indigenous species left on the Island. However, fossil remains show that tuart, marri, jarrah, banksia and she-oaks once grew there. The plants that remain are all hardy and are able to withstand the exposure of the Island and adapt to high salinity levels.
Along the coastline plants known as "sea rocket" (a widely distributed beach plant), spinifex and the aromatic wild rosemary can be found. On the grassy plain there is a dominant tussock grass interspersed with prickle lily, the mauve and yellow coloured stilt plants and the blue Rottnest daisy, also known as the blue lace flower. On the salt lake shores an array of salt-water tolerant plants such as samphires, halosarcia, the broadleaf grey salt bush, sedges and templetonia can be found.
In addition to Rottnest Island's three native woodland species (the Rottnest Island Pine, Melaleuca lanceolata and Acacia rostellifra) there are many introduced varieties such as Norfolk Island pines, Morton Bay figs, Aleppo pines, olive trees, palm trees and tuarts. Other introduced plants include two varieties of onion weeds that are primary colonisers and a Mediterranean grass (Lagurus ovatus), commonly known as hare's tail grass.
A well known flower native to Rottnest Island, the Rottnest daisy (Trachymene coerulea), is actually a member of the carrot family, although it resembles a true daisy in its form. The Rottnest daisy is only found in the wild in Western Australia, although it is now grown througout the world as an ornamental garden plant.
Early descriptions of Rottnest Island flora are inconsistent. In 1658 a Dutch sea captain, Samuel Volkersen, described the Island as "well wooded". In 1696, another Dutch sea captain, Willem De Vlamingh, who walked towards the centre of the Island, recorded "bare rocky soils and fine plains". In 1822, a few years before the Swan River colony was first established, James Cunningham, a botanist, described the Island as covered with Rottnest Island Pine trees and Melaleuca. A few years after colonisation, in 1835, Thomas Bradford Wilson, a stockman living on the Island, referred to hummocks and sandhills devoid of vegetation.
European settlers quickly changed the landscape of Rottnest. Land was cleared and tracks made. Firewood was gathered, especially for the salt works, and the Island was repeatedly burned. Aboriginal prisoners often used fires as an aid in hunting quokkas.
In the late 1920s the quokka population was protected and began to soar, grazing heavily on the palatable Acacia rostellifera. The impact of fire and quokka grazing has resulted in a tremendous reduction in the Island's forest cover. It is estimated that in 1919 about half the Island (950ha) was covered with native Acacia rostellifra. By 1941 this had shrunk to 400ha, and by 1974 only 130ha (6.8 per cent) of the Island remained naturally wooded.
The last 6,000 years have probably seen 90 per cent of the plant species on Rottnest Island eliminated by salt, wind and sand. The past 150 years have been marked by fire and wood collecting by man, and the last 50 years by heavy grazing by quokkas.
Today, the Rottnest Island Authority is actively "re-greening" the Island. Planned restoration of the Island's woodlands is occurring. Rottnest Island pine (Callitris preissii) and Rottnest Island tea tree (Melaleuca lanceolata) seedlings are being planted, as well as direct seeding to both of these and other species of plants native to Rottnest. Planted areas are protected from quokkas by fencing. Areas on the Island are selected, fenced against quokkas and then either planted or seeded in winter or allowed to regenerate naturally.