Botany

Jarrah Trees



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The four dominant tree species of the south west of Western Australia are jarrah, karri, tingle and tuart.  These are all unique to the state and the forest regions of each species are home to a very diverse range of fauna and other flora species. Some 150 different bird varieties, 29 mammals, 45 reptiles and over 1,200 plants and wildflowers are supported by the jarrah forest ecosystem. 

The jarrah has the scientific name of Eucalyptus marginata.  ‘Marginata’ refers to the light-coloured vein bordering the leaves. The jarrah can grow up to 40 metres (130 feet) in height.  It is a long-living tree, with specimens living up to 1,000 years. The timber is beautifully grained and beautifully coloured ranging from light orange or pinkish browns to a deep, rich, reddish/burgundy brown.  The trunk is long and straight.  These attributes, as well as the fact that it is very durable, makes it perfect for a number of uses including construction, fencing, furniture making and wood-working. It is estimated that around half of the jarrah forests that covered an area of 3.9 million hectares south of the capital, Perth, have been destroyed by extensive logging and clearing. Railway sleepers were manufactured in their thousands from the jarrah forests and even today, jarrah cobblestones can still be found in London and Berlin. 

Eucalyptus marginata is one of the most common of the eucalypts to be found in the south-west of Western Australia.  ‘Jarrah’ is an aboriginal word. In the 1800s, jarrah was known as Swan River mahogany, the name coming from the Swan River which runs through Perth and because worked jarrah has a similar appearance to the Honduras mahogany tree. While it is sometimes confused with karri, jarrah forms charcoal when burnt whereas karri burns to a white ash.  Karri also has much less resistance to termites.

The trunk has a diameter of 3 metres (9.8ft). The rough, fibrous bark is vertically grooved and greyish-brown in colour. Each season, the bark is shed by splitting into long, flat strips. The leaves are 8 to 13cms long and 1.5 to 3cms broad.  The leaves are often curved and are a shiny, dark green on the upper surfaces with a paler undersurface. Stalked flower buds appear in clusters of between 7 and 11.  A narrow, conical bud cap 5 to 9 mm long covers each bud. White or cream flowers measuring 1 to 2cms in diameter appear in spring and early summer.  The fruits vary from spherical to barrel-shaped and have a length and breadth ranging from 9 to 16 mms long. When the flower is spent, the nut often falls to the floor of the forest. 

The jarrah is unusual in having lignotubers (large underground swellings) which attach to the underground root system.  The lignotubers store carbohydrates and help young trees to regenerate after a fire.  The bark has insulating qualities that help protect the tree from bushfires. The tap-root of the jarrah may be as long as 40 metres.  This gives great drought resistance allowing the tree to draw water from deep down during dry periods. The jarrah is susceptible to ‘dieback’, a disease which causes root-rot.  Various restrictions on the movement of traffic through susceptible areas have been introduced in an effort to control the spread of the disease. 

The jarrah is adaptable to a range of soil types and ecologic zones. It provides numerous habitats for birds and bees especially.  As the heartwood decays, the hollows are sought as nests by birds and tree-dwelling mammals.  Once a jarrah has fallen, the hollow trunk and branches are ideal homes for small mammals such as the chuditch and numbat. 

 Honey from bees kept in the jarrah forests is very popular. It is a rich, deep red with a rich flavour. But it is as a building source and as timber that jarrah has gained most fame.  The timber is dense, heavy and termite-resistant and is well regarded for cabinet making, flooring, hot tubs and outdoor furniture. The timber is easily worked whilst green but becomes so hard when seasoned that conventional tools are all but useless.  It is incredibly strong and durable and, being resistant to some species of marine borers and worms, has been used for bridges, wharves and ship building. Percussion instruments and guitar inlays are also fashioned from the versatile jarrah. Even the gumnuts are used for art and craft pursuits.   

During the early days of Western Australia’s timber industry, much jarrah was exported to the United Kingdom where it was cut into blocks and covered with asphalt for roads.  It was also used for cobblestones. Even recycled jarrah is in demand for furniture making and wood-working. It is an excellent wood for stoves and heating, generating more heat than most other available woods. 

The little town of Nannup is nestled in a fine area of jarrah. The Collie River valley and much of the south west are also home to good examples of jarrah forests. The Forest Heritage Centre in Dwellingup has walks through a mixed jarrah/marri forest and a very interesting Canopy Tree Top Walk.

 Sources:
www.rustrees.com
en.wikipedia.org



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