The jarrah (Eucalyptus marginata Donn. ex Smith) forest in Western Australia is a tall dry sclerophyll forest with a uniform overstorey dominated by jarrah. The forest extends over most of the south-western corner of Australia, with a Mediterranean climate, covering approximately 64 000 km2 (Shearer and Tippett, 1989). Jarrah ranges in height from 15-50 m and 3 m in diameter across most of its range. Jarrah has the ability to dominate a wide range of sites, especially lateritic catenas. The jarrah forest has a high level of endemism in plants. There are approximately 1200 species found over its range, including many species in the Myrtaceae, Fabaceae and Proteaceae (Shearer and Tippett, 1989). Jarrah has, and will, continue to be an important timber species because of its durability and suitability for furniture, shipbuilding, wharves, telegraph poles and structural timber in house building. Jarrah is an important ‘keystone’ species of the jarrah forest and any threats to its health and viability will have important economic, environmental and ecological consequences. The most signifi cant threat to jarrah is the introduced soilborne plant pathogen Phytophthora cinnamomi Rands.