On mature reflection: Ozone damage can be detected in oak trees by hyperspectral reflectance

• Wytham woods has significantly higher ozone (O 3 ) than BIFoR FACE forest. • O 3 induced changes in leaf reflectance can be identified in mature Quercus robur . • O 3 affected green reflectance peak and red-edge reflectance of leaves. • Hyperspectral monitoring is a new method of detecting O 3 damage to forests. At the near-surface, ozone (O 3 ) is a toxic pollutant which has reached dangerously high concentrations across the world and is predicted to continue to rise. O 3 reduces the growth, productivity and resilience of trees but the extent of O 3 damage to forests is uncertain. To develop a high throughput method of monitoring O 3 damage to forests, we pioneer hyperspectral monitoring of O 3 damage in adult oak trees across a range of naturally occurring O 3 concentrations. Using a machine learning approach, we demonstrate accurate prediction of O 3 exposure of trees from hyperspectral leaf reflectance alone. This method could be used for forest level assessments of O 3 damage. Vegetation indices characterising green reflectance and red-edge track O 3 induced changes in leaf reflectance. Vegetation indices have the potential to scale up O 3 damage monitoring across spatial scales. As O 3 concentrations continue to rise globally, understanding the extent of O 3 damage to forests is crucial to effectively harness the carbon sequestration potential of forests. We demonstrate the exciting potential of spectral monitoring of O 3 damage in mature trees under natural conditions.