Department of Electrical and Computer Engineering Seminar Series

Why are our Pine Trees going red? Analysis using a preferred systems modelling approach.


Prof Graeme Wake


School of Natural and Computational Sciences, Senior Research Fellow and Emeritus Professor of Industrial Mathematics, Massey University in Auckland & Hamilton

Time & Place

Fri, 12 Jul 2019 14:00:00 NZST in Link 309 Lecture Theatre


Red needle cast was first detected in New Zealand in 2008 but it was probably present in forests for a few years before that. It is caused by a strain of phytohthora that results in pine needles turning red and being shed prematurely. A tree without needles does not grow very much and can die. The disease can cause up to forty percent growth loss in a year. The origin of red needle cast in New Zealand has been traced to Oregon in the United States. It was transported here in plant material and on forestry machinery. A simple systems model has been proposed to understand and quantify the onset and epidemiology of red needle cast in radiata pine. This is proving to be a more useful than a “normal” empirical approach. Some explanation of this will be given in the context of this example. The disease is impacting much of the New Zealand forestry estate being driven through the production of
self-replicating spores which are dispersed with water. The first model is deterministic, not spatially or agestructured, and initially not including seasonal or environmental effects. This model showed the clear existence of calculable thresholds for disease proliferation and elimination. It is to be used to identify thresholds for infection to spread or to disappear. In this paper the established model which previously had neglected the crucial effects of the environment, is generalised to include seasonal effects. The weather cycle drives the solution to produce in some cases quite different long-term outcomes, depending on the external parameters. The system is now non-autonomous, with weather imposed, with yearly periodicity. Coexisting stable longterm solutions are also then driven to exhibit this periodicity. Some relevant theory will be given. This will be used to underpin the schedule for optimal spraying.

Supported by MBIE contract No. C04X1305 Healthy Trees, Healthy Future Enabling Technologies
programme. Co-authors: Rebecca Turner & Nari Williams (Scion), Penelope Bilton (Proteus), and Tony
Pleasants (Massey University)


Graeme Wake

  • is currently a Senior Research Fellow and Emeritus Professor of Industrial Mathematics at Massey University in Auckland & Hamilton
  • was a Postdoctoral Scholar at University of Oxford
  • has published about 250 publications and supervised 60 PhD students
  • specialises in Industrial Mathematics and applications in Agriculture, Ecology, Medicine, and Spontaneous Combustion, and is involved in commercial research consultancy.