Life on the rocks

Granite rock formations are often prominent in Australian landscapes, for example in Girraween National Park in Queensland, Wilsons Promontory in Victoria and Mt Franklin in Western Australia. In arid areas waterholes in granite outcrops were significant in summer for Aboriginals (Plate 23.1).

There are considerable similarities between granite outcrops across a wide range of climates. All have poor soils of restricted volume, severe fluctuations between wet and dry conditions, low levels of soil nutrients, high insolation (light intensity) and exposure to strong winds. However, as in any harsh environment, species with specialist adaptations survive and even thrive.

Algae and lichens colonise the rock surface and may be overgrown by mosses. These plant forms and some ferns and flowering plants (such as the pincushion (Borya spp.) and the feather flower (Verticordia staminosa)) can desiccate completely in the dry season, but revitalise and function again hours after rewetting. More commonly, plants die down to seed or rootstock in the dry period. The insectivorous sundew (Drosera spp.), which catches and digests insects for extra nutrients, particularly nitrogen, survives summer as an underground tuber. Other plants such as the elbow orchid (Spiculea ciliata) are succulents, storing water to persist for some time into the summer. Shrubs and trees on granite outcrops use water conservatively most of the year and need access to rock cracks for water over the dry season.