As Chemical Thinning becomes increasingly popular amongst New Zealand forest managers, the Precision Silviculture Programme in partnership with BSI | Scion Group and Matariki Forests commissioned a study on detecting early herbicide-induced stress in radiata pine using hyperspectral and multispectral sensors on unmanned aerial vehicles (UAVs). Chemical thinning can be particularly useful in steep or inaccessible terrain and assessing its effectiveness remotely is a good way to reduce risk whilst monitoring operations. Getting early data on the success of the operation is important operationally so contractors can be paid as early as possible and strategically to ensure an accurate revised final crop stocking can be generated.
This study establishes a foundational contribution to advancing early, pre-visual, detection of stress responses in trees, offering valuable potential for forest health monitoring and herbicide management. Stress was detected using the advanced hyperspectral camera at 13 days post treatment, while the multispectral camera picked it up 18 days post treatment. Key indicators are changes in leaf pigments, which signal stress before visible canopy symptoms appear. This 13-to-18-day window is crucial for early detection and future monitoring. It was important to include multispectral imagery as this is more readily deployed in forestry operations today where hyperspectral cameras are still largely only used in the research domain. The research led by Dr Russell Main from BSI Scion Group has been published in the peer review journal ‘Forests’.
Dr Michael Watt of BSI Scion Group notes that “this was the first study internationally to use hyperspectral imagery to detect herbicide induced stress within a commercial forest, illustrating the groundbreaking nature of the research”.
Remote sensing technologies are continually improving and are a lower cost, easy to deploy technique for monitoring tree stress. This study was focussed on ‘whether UAV-based spectral imaging could be used to detect early signs of herbicide-induced stress in a chemically thinned radiata pine stand’.
The FGR Report details the study methodology, including the experiment design and implementation. Visit the FGR website to read the full report.
