RA3 REPORT: Kauri dieback impact on beetles

The effect of kauri dieback on a diverse beetle community

March 2024

Wardhaugh C, Black H. 2024. The effect of kauri dieback on a diverse beetle community. A report for New Zealand’s Biological Heritage National Science Challenge: Ngā Rākau Taketake. 38 p.

NOTE:

This report is embargoed until 31/01/2025 or until a paper is published. For further information please contact Carl Wardhaugh at Scion Research

EXECUTIVE SUMMARY

The problem

Kauri dieback, caused by the soil-borne fungal pathogen Phytophthora agathidicida, has spread through much of New Zealand’s kauri forests, killing thousands of trees. The impact of the loss of numerous canopy trees on the wider biological communities in kauri forests is largely unknown. Here we undertake an initial survey of the beetle fauna in symptomatic forest with widespread dieback of kauri trees, and asymptomatic forest with little or no dieback, to ascertain whether the loss of kauri trees is having any noticeable impact on this diverse community.

Key results

Overall, we collected 1,696 individual beetles from 228 species. Diversity did not differ between asymptomatic and symptomatic sites, but beetle abundance was much higher in asymptomatic areas. This pattern was driven by higher abundances of fungivorous, predatory, and herbivorous species in asymptomatic sites. Conversely, the abundances and diversity of species we expected to benefit from the widespread deaths of kauri trees (e.g., xylophages) did not differ among sites. The broad range of species with lower abundances in areas with kauri dieback that are not directly reliant on kauri trees suggests that abundance patterns are being influenced by changes to abiotic conditions caused by the loss of dominant canopy trees, rather than the loss of kauri per se.

Implications of results for the client

While these communities may recover somewhat with the replacement of kauri by other tree species as the dominant canopy species at these sites, beetle communities will likely be forever changed by the loss of kauri trees.

Further work

Continued monitoring of insect communities, either continuously or at regular intervals, is recommended to track how these ecologically vital assemblages change as the forest changes due to kauri dieback disease.