The incidence and spatial pattern of Nothofagus cunninghamii (Hook.) Oerst. attacked by Platypus subgranosus Schedl in Tasmania's cool temperate rainforest

Abstract

Abstract Data from transect surveys of 20 cool temperate rainforest sites in Tasmania were used to quantify the incidence and spatial distribution of myrtle, Nothofagus cunninghamii, attacked by the mountain pinhole borer, Platypus subgranosus. Attack by this insect is indicative of the disease ‘myrtle wilt’ caused by the pathogenic hyphomycete, Chalara australis.The proportion of myrtle trees attacked by the disease ranged from 9.4 to 53.4%, with an average incidence of 24.6%. Regression analysis indicated that attack decreased with increasing altitude and, after adjusting for altitude, callidendrous forests had a higher incidence of attack than thamnic‐implicate forests. In mixed eucalypt‐rainforest stands, the incidence of attack increased as both relative and absolute measures of myrtle density increased. However, a significant amount of variation in the incidence of attack remained unexplained by the site and stand variables measured. The incidence of attack differed significantly between diameter classes with the larger diameter trees having the highest incidence of attack. Trees with stem and crown damage had a significantly higher incidence of attack than undamaged trees. Attacked trees tended to be clumped, with the degree of clumping reasonably constant across sites, but dependent on nearest neighbour distance within sites.Dying trees occurred at an average rate of 2.4 trees ha‐1 per year or 1.6% of live trees per year across the sites.