Researchers demonstrated that advanced sensors carried on UAVs (Unmanned Aerial Vehicles) can be used to help scientists monitor the impact of myrtle rust on susceptible species. They showed that the technology could be used to assess disease impacts in the upper parts of the forest canopy that would otherwise be inaccessible.
There is potential for this technology to capture valuable structural and health-related data that can assist in monitoring the long-term impacts of myrtle rust on our forests at multiple scales.
Researchers also successfully tested new methods to rapidly map susceptible host species using AI-powered computer vision algorithms trained to detect key species over large areas.
These techniques will give scientists and conservationists new tools to detect and monitor the impacts of myrtle rust so that we can better manage the disease and protect our vulnerable myrtle species.
Download the report: Developing improved methods for mapping Metrosideros species in New Zealand
New Zealand has 27 recognised native species of myrtles that may be susceptible to myrtle rust, but little work had been done to understand the distribution of these species at a national scale.
This study set out to develop national-scale species distribution models for native myrtle species using a consistent, standardised approach to predict the likelihood of finding an individual myrtle species at a particular location, and to understand what environmental variables drive their national distribution.
Models were developed for 22 myrtle species that occur on New Zealand’s three main islands, surrounding inshore islands, and a limited number of offshore islands. From these models, researchers predicted each species’ distribution.
Climate variables were the most informative predictors for most species, but landscape and soil variables also contributed.
The predicted distributions superficially followed the known distributions for most species, including depicting the northern populations of southern rātā (i.e. on the Coromandel Peninsula), which previous modelling approaches have found challenging to replicate.
The predicted distributions for all species are presented in the report as separately supplied spatial data files, and through an online visualisation interface.
Download the report: Species distribution models of the native New Zealand Myrtaceae
There are over 200 myrtle species in New Zealand, of which approximately 30 are native. The distribution and density of myrtles in urban, rural and native environments varies across the country.
This report outlines potential species of myrtles that could be used as indicator species for surveillance for rapid assessment of the spread and impact of myrtle rust across New Zealand.
The researchers found that ramarama is a good candidate for an indicator species for myrtle rust. As well as having high susceptibility, the species is found across New Zealand in urban and native environments. The key limitation is the size of the plants. As a shrub it might not be a suitable choice for remote sensing techniques and further research should examine if this is the case.
The second selection for an indicator species for surveillance is pōhutukawa, although its distribution predominantly in the northern part of the North Island make it an unsuitable indicator species for the entire country. Researchers found that a further two species, rata and lilly pilly, could also potentially be used as indicator species.
Download the report: Selection of indicator species for surveillance
A new on-line surveillance form will enable trained observers to undertake monitoring of myrtle rust to track its impact on trees and eco-systems over time. Ongoing long-term surveillance across New Zealand is critical to understand where the disease has spread to and how severe it is. The new form will make sure that the right kind of information is consistently being collected, and importantly, will allow for future data merging between different user groups such as the Department of Conservation, councils and botanical gardens.
Researchers co-designed the form in a series of hui with scientists, mana whenua, councils, industry groups and government organisations that have a long-term interest in fighting myrtle rust. This report includes a global host list.
Localised extinction possible
Researchers used the form to monitor the rust in a naturally occurring stand of myrtle plants. They say the results are concerning and warn localised extinction of some myrtle species is possible.
Download the report: Improved myrtle rust surveillance
(the surveillance form is Appendix A)
Download: Global host list