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 around 1,500 native species flourish. It is believed that Rottnest Island was separated from the mainland approximately 7,000 years ago.
The sea-level rose, cutting the island off from the land mass. 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 native plants that remain are well adapted to the predominantly nutrient poor soils, along with the salty and often windy conditions.
The vegetation of Rottnest Island is dominated by the prickle lily (Acanthocarpus preissii) and feather speargrass (Austrostipa flavescens) heath community, which occurs in areas previously dominated by woodland. Over 60% of the Island is covered by this heath assemblage, with the summer-scented wattle (Acacia rostellifera) forming a closed scrub in association with the heath.
The woodland community on Rottnest comprises Rottnest Island Pine (Callitris preissii) and Rottnest Island Tea Tree (Melaleuca lanceolata). Prior to European settlement in 1831, over half of Rottnest Island was covered in large areas of woodland. 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. At present, approximately 4% of the Island is covered by scattered relic stands of woodland.
Along the coastline plants such as beach spinifex (Spinifex longifolius), the aromatic coastal rosemary (Westringia dampieri), coastal sword-sedge (Lepidosperma gladiatum), seaberry saltbush (Rhagodia baccata), and thick-leaved fan-flower (Scaevola crassifolia) can be found. On the salt lake shores an array of salt-water tolerant plants such as samphires, grey salt bush, and sedges can be found.
A well-known flower native to Rottnest Island, the Rottnest Island daisy (Trachymene coerulea subsp. coerulea), is actually a member of the carrot family, although it resembles a true daisy in its form. Fields of these bright purple flowers appear in spring and areas of Rottnest are transformed into carpets of purple. Although the daisy can be seen in most areas of the island, the dune areas behind Henrietta Rocks and Parker Point are especially attractive.
In addition to Rottnest Island's native woodland species there are many introduced varieties such as Norfolk Island pines, Moreton Bay figs, Aleppo pines, olive trees, palm trees and tuarts. Other introduced plants include two varieties of onion weeds that are primary colonisers, and hare’s tail grass (Lagurus ovatus).
The Rottnest Island Authority has been undertaking woodland restoration on Rottnest since 1963. Woodland restoration activities include seed collection, propagation, planting and weed control. In earlier years, tree species not naturally occurring on Rottnest such as tuart (Eucalyptus gomphocephala) and coastal moort (Eucalyptus utilis) were planted in large stands. Apart from these stands not being representative of the natural habitat, many of these non-native species are not suited to the Island’s harsh conditions. Species such as tuart have high water demands and as a result put additional pressures on Rottnest’s limited groundwater supply.
Since 1995, only the two tree species native to the Island, Rottnest Island Pine and Rottnest Island Tea Tree, have been planted. Woodland restoration on Rottnest to date has predominantly involved planting within fenced restoration areas in order to exclude quokkas from grazing on the seedlings.