This is the third survey carried out by Auckland Council on the Waitakere Ranges Regional Park for kauri dieback disease.
Remote sensing was used to detect kauri trees >15m tall within the forest canopy of Te Wao Nui Tiriwa/ the Waitakere Ranges parkland. . It is unknown how many kauri shorter than 15 m are within the Waitakere Ranges as they were not easily detectable with remote sensing technologies available in 2020/21. The research surveyed a representative sample of 2140 trees, out of 68,420 identified within the forest. The soil beneath 761 of these trees were tested for P. agathidicida presence.
The baseline pathogen prevalence of P. agathidicida detection was 76/761 (10%) in soil samples, and kauri dieback symptoms in 16.5% of surveyed trees. The spatial distribution of P. agathidicida from the 761 soil sampled trees showed a greater density of P. agathidicida detections in the northern, central-western and southern borders of the study area. There was no detection of P. agathidicida in the central interior areas of the Park.
An interesting finding was that kauri seedlings and saplings were surviving in soils where P. agathidicida was confirmed. This study provides a consistent cohort of monitored trees that can be remeasured to understand change in disease and pathogen prevalence over time.
The results supported the precautionary approach taken since 2018 and continued measures to stop the spread of Phytophthora agathidicida.