Remote sensing wattle rust induced defoliation across black wattle timber plantations in Southern Africa

ABSTRACT

The detection and monitoring of lethal pathogenic funguses are important for effectively deploying suppressive measures to sudden and severe outbreaks in plantation forestry. This study successfully investigated the utility of Landsat 8 multispectral satellite imagery to map Uromycladium acacia (wattle rust) induced canopy defoliation across black wattle plantations. The framework developed for the provincial assessment of rust damage proved to be effective by using data collected from field monitoring plots over the year 2015 and 2016. Using a powerful Gradient Boosting Machine (GBM) approach, rust occurrences were mapped at accuracies of 69% for March and 72% for November when using the 2015 dataset and 77% for March and 81% for November using the 2016 dataset. Individual class accuracies for varying levels of defoliation were also evaluated. When aggregating the field and image datasets, a two-year probability map revealed the likelihood of rust defoliation across the black wattle plantation region. Overall, the study showcased the robustness and cost-effectiveness of using multispectral remote sensing methodologies for repeatable forest health monitoring in key commercial forest plantations.

KEYWORDS:

• Multispectral remote sensing
• black wattle
• Uromycladium acacia

Acknowledgements

The authors would like to recognize the contribution and support of the Wattle Rust Steering Committee and the valuable assistance and advice of Mr Johan Nel from TWK. The Department of Science and Technology (DST) is acknowledged for making this project financially possible through the Sector Innovation Fund (SIF) and via Forestry South Africa (FSA). The initiative and input from the various industry partners, NCT Forestry and collaborators is also greatly appreciated. The support from the National Research Foundation (NRF) of South Africa (grant number 114898 and 127354) is also acknowledged.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The work was supported by the National Research Foundation South Africa [114898 and 127354].