Dieback of stringybark eucalypt forests in the Mount Lofty Ranges

Abstract

ABSTRACT Canopy dieback and tree mortality are occurring in forests of the Mount Lofty Ranges (MLR), South Australia, dominated by Eucalyptus baxteri (Brown Stringybark) and E. obliqua (Messmate Stringybark). The extent and causes of decline are not fully understood, prohibiting evidence-based management. We explored the geographic and climatic distributions of MLR stringybark populations relative to eastern populations. We conducted field assessments of dieback aetiology, and analysed existing monitoring data. The MLR stringybarks are disjunct from eastern populations and occupy a more summer-arid niche. The species are susceptible to water stress and Phytophthora. Droughts during 2006–2009 and 2018–2019 may have contributed to dieback. However, field assessments suggest a complex landscape syndrome involving borer infestations and fire impacts among other factors, rather than solely hydraulic failure. Messmate Stringybark has suffered widespread, patchy stand collapse with no obvious common pattern with respect to topography or water availability, although northern range-edge sites are heavily affected. Brown Stringybark is less affected but has notable collapse sites. Further investigations should include regional surveys to record spatial and temporal patterns of tree mortality combined with remote sensing. Our findings confirm the susceptibility of stringybark forests to ecosystem collapse and highlight the need to better understand underlying causes.