Aerial surveillance to detect kauri dieback in New Zealand

Abstract

The causal agent of kauri dieback, Phytophthora 'taxon Agathis' (PTA), poses a significant threat to kauri (Agathis australis) in northern New Zealand. Ground-based field surveys have previously confirmed PTA presence at several locations across Auckland and Northland. However, ground surveys are limited to areas adjacent to tracks because of difficulty and cost associated with off-track access in steep terrain, along with concern about furthering spread of PTA. A methodology for aerial photographic surveillance of kauri dieback was developed and implemented in Waita¯kere Ranges, Hunua Ranges and adjacent forest areas. Using recently developed GPS technology, photographs were embedded with position data so unhealthy trees were easily located later for ground-truthing. Aerial survey was found to be a time- and cost-effective method for surveying large, inaccessible areas of forest for kauri dieback. The methodology would also be applicable for detection of visible disease or damage symptoms in other canopy tree species.