in tree hollows will not do so until trees are big enough and old enough to have sufficient hollows. Jarrah is a slow growing species and 130 years can be considered the minimum age for the development of appropriate hollows in jarrah and marri. The loss of forest for agriculture and timber has resulted in diminishing population numbers of many fauna species. Nine mammal and seventeen bird species are obligate users of tree hollows. Species that use large hollows usually have a relatively small home range and depend on their hollows for breeding. These species are most likely to be negatively impacted by logging. Roost sites (hollows) are critical for the persistence of insectivorous bats living in Jarrah Forest. Spending a large portion of their lives in roosts, they are used as diurnal shelters, shelter during maternity, and shelter for bachelors, migrating and hibernation sites. Facilitating complex social interactions including information transfer, roost sites also act as breeding sites, they provide protection from bad weather and predators, they minimise parasite load and promote energy conservation. Disease Prevalent in the northern areas of Jarrah Forest, dieback disease, caused by the introduced soil-borne pathogen Phytophthora cinnamomi, is a serious threat to many plant species. The disease involves the formation of lesions (decaying tissue) starting in the roots and moving up the stem of a plant, and, in the case of many species, killing them. It negatively affects more than 22% of the plant species in the forest. P. cinnamomi has been found in suberized and partially suberized roots that are perennial and it is these roots that form the specialised feeder root system of the jarrah. The spread of dieback is exacerbated by altered drainage caused by mining and timber harvesting. The soil population of P. cinnamomi is generally highest during spring, the time of year when soil temperature and moisture levels are high. An increase in summer rainfall is likely to increase the harm that this pathogen causes in the northern and southern jarrah forests, with high mortality rates of jarrah expected. Management FORESTCHECK is a Department of Parks and Wildlife initiative that is responsible for monitoring biodiversity in the jarrah forests of south-west Western Australia. Monitoring total species richness, abundance and composition FORESTCHECK is designed to provide forest managers with accurate accounts of changes and trends in biodiversity associated with management activities. FORESTCHECK use four Jarrah Forest ecosystems that reflect