Sclerophyll

Sclerophyll is a type of vegetation that has hard leaves and short internodes (the distance between leaves along the stem). The word comes from the Greek sclero (hard) and phyllon (leaf). Sclerophyllous plants occur in all parts of the world but are most typical of Australia. They are also prominent in the Mediterranean forests, woodlands, and shrub biome that covers the Mediterranean Basin, Californian woodlands, Chilean Matorral, the Cape Province of South Africa, southern Western Australia, and western Southern Australia.

Australian bush

Arid, largely treeless areas aside, most Australian bushland is sclerophyll forest. Common plants include the Proteaceae (Grevilleas, Banksias and Proteas), tea-trees, Acacias, Boronias, and the Eucalypts.

The ubiquitous dry sclerophyll forests covered vast areas of the continent (and to a much lesser extent still do). They have a eucalyptus overstory (10 to 30 metres) and the understory is also hard-leaved. Often seeming drab and barren to the casual European eye, dry sclerophyll forest is highly complex and diverse, with up to twice as many different plant species per square metre as rainforest, and high animal diversity too. (If at first this seems counter-intuitive, remember that, as a broad generalisation, harsher conditions promote speciation and diversity, with every tiny variation in soil, light, or moisture offering a niche, where rich soils and ample water tend to simply favour species which can take advantage of them most rapidly.)

The less extensive wet sclerophyll forests have a taller eucalyptus overstory, 30 metres or more (typically Mountain Ash, Alpine Ash, Messmate Stringybark or Manna Gum), and a soft-leaved, fairly open understory (tree ferns are common). They require ample rainfall — at least 1000mm (40 inches).

History

Sclerophyllous plants are anything but newcomers — the Proteaceae family dates back 80 million years to the late Cretaceous—but sclerophyll forests did not start becoming a major part of the Australian landscape until around 15 million years ago. By the time of European settlement, sclerophyll forest accounted for the vast bulk of the forested areas.

Most of the wooded parts of present-day Australia have become sclerophyll forest as a result of the extreme age of the continent. Deep weathering of the crust over many millions of years leached chemicals out of the rock, leaving Australian soils deficient in nutrients, particularly phosphorus. (Small areas, mostly in the south, have benefited from relatively recent volcanic activity and have fairly rich soils as a result.)

Sclerophyllous plants generally resist dry conditions well, making them successful in areas of mediterranean climate with rainy winters but hot dry summers. In Australia, however, they evolved in response to the low level of phosphorus in the soil — indeed, many Australian native plants cannot tolerate higher levels of phosphorus and will die if fertilised incorrectly. The leaves are hard due to lignin, which prevents wilting and allows plants to grow even when there isn't enough phosphorus for substantial new cell growth (Major, 2003).

References

• R. Major (2003). "Sclerophyll forests". Australian Museum. Retrieved 2005-02-14.