Biodiversity of canopy arthropods in Jarrah forest of south-west Western Australia: review of ecological theory and conservation management

Abstract

A theory proposed in 1996 by Recher, Majer and Ganesh linking biodiversity of forest canopy arthropods to site productivity is analysed. Available evidence from Jarrah Eucalyptus marginata forest is inconsistent with this model. We instead propose that increased habitat variety and temperature and rainfall clines are the major environmental factors that determine canopy arthropod species richness. Biodiversity gradients for mammal, landbird and reptile species across south-west Western Australia appear to provide an appropriate model for forest insect faunas. These gradients predict that the most diverse canopy fauna should occur in the eastern Jarrah and Wandoo forests. Precautionary forest management policies and procedures currently in place to conserve the poorly collected and inadequately known arthropod fauna of tree crowns in Jarrah forest are summarized and discussed. In essence, these maximize habitat diversity at landscape scales. Major conservation threats are considered to be factors that reduce leaf area at large spatial (Phytophthora infection) and temporal scales (summer wildfire and defoliating insect outbreaks). Logging is not considered significant because it is constrained to small spatial scales (10 ha for the most extreme treatment) and long return times (2-3 decades).