MADCA Eucalyptus marginata Donn ex Smith family Myrtaceae
Eucalyptus marginata is one of the most important hardwoods of Australia. In Western Australia it represents about two-thirds of the annual production of sawn timber. Under optimum conditions it is a tall tree attaining 30—40 m in height with dbh up to 2 m. The commercial bole length rarely exceeds one-half of the total height. On poor sites the species is reduced to a Mallee form.
Jarrah grows in the southwest of the State and the production area (about 1—2 million hectares) coincides closely with that for Western Australian blackbutt (E. patens). The prime Jarrah area is a belt 30—50 km wide, which extends along the Darling Range from Chidlows Well some 50 km east of Perth, southwards to the vicinity of Albany. This belt is bounded by the Darling escarpment on the western side and approximately by the 630 mm isohyet on the eastern. Most of this area is now State forest. There are a few eastern outliers such as Tutanning Reserve southeast of Pingelly and Jilakin Rock east of Kulin. The latitudinal range is 30—35°S and the altitude for the best forests is from 100 to about 300 m at the far north of its distribution. The climate is warm humid to
warm sub-humid, with mean maximum temperatures for the hottest month around 25-31°C and mean minimum temperatures for the coldest month around 5—9°C. Up to 12 frosts a year may be experienced in some areas away from the coast. Mean annual rainfall is about 700—1250 mm with a winter maximum.
Jarrah has its best development and greatest size on red loams of deeply dissected river valleys between the Murray and Warren Rivers. Clay forms the subsoil and where this is exposed by erosion the species gives way to other eucalypts. Abundant but poorer quality Jarrah, producing smaller logs of easy extraction, occurs on the Donnybrook Sunkland, a low plateau south of Busselton. On the better soils of the south it is replaced by Karri (Eucalyptus diversicolor) or Marri (E. calophylla) while on limestone ridges it is replaced by tuart (E. gomphocephala). On poor, deep sands height is reduced and it is only of Mallee form near Mt Lesueur.
A feature of Jarrah is its occurrence in pure or almost pure stands and the Jarrah forests of the northern Darling Range provide invaluable watershed protection. On the drier, eastern side of the occurrence where Jarrah becomes progressively smaller, there is limited association with wandoo (E. wandoo), powder bark wandoo (E. accedens) and York gum (E. loxophleba) before it is entirely replaced by them.
The species has suffered badly from Jarrah dieback caused by the fungus Phytophthora cinnamomi and forest quarantine measures have had to be implemented to restrict the spread of