remote sensing of european spruce (ips typographus, L.) bark beetle green attack
Haidi Abdullah is a PhD student in the Department Natural Resources. Her supervisor is prof.dr. A.K. Skidmore from the faculty of Geo-information Science and Earth Observation.
Forest disturbance in Europe, induced by the European spruce bark beetle Ips typographus, L., results in regional-scale dieback and causes major economic loss to the forest industry, particularly in Norway Spruce (Picea abies) forest stands. Early stress detection induced by bark beetle infestation (the so-called ‘green-attack’ stage — when trees are yet to show distinct symptoms observable by the human eye) is crucial and can lead to effective forest management and reduce economic losses. In this respect, remote sensing is a cost-effective and repetitive technique which offers an optimal approach for monitoring and assessing forest stress in comparison to the more traditional (field survey) approach, which is not practical and is inefficient in large areas because it is significantly laborious and costly.
The current thesis presents research regarding the potential of different types of remote sensing data obtained from a variety of sensors, including ASD FieldSpec3 and multispectral satellites (RapidEye, SPOT-5, Sentinel-2 and Landsat-8) for early detection of bark beetle infestation at both leaf and canopy levels. Moreover, the research provided an important opportunity to advance understanding regarding the impact of early bark beetle infestation on the biochemical properties of infested trees (chlorophyll, nitrogen, chlorophyll fluoresces, leaf water content, dry matter content and stomatal conductance).
The leaf-level spectrometry demonstrated that a significant difference (p < 0.05) exists in the mean reflectance spectra between healthy and infested needle samples at the green-attack stage, with the most pronounced differences being observed in the NIR and SWIR regions. The results of our analysis demonstrated that infestation at the green-attack stage reduced the foliar biochemical concentrations (chlorophyll and nitrogen) and weakened their correlations with reflectance. The findings confirmed the importance of hyperspectral measurement as well as foliar biochemical properties (i.e. chlorophyll and nitrogen) for the detection of Ips typographus, L. at the green-attack stage.
Furthermore, research has moved on to the spaceborne level to evaluate the potential of different types of multispectral satellite data (RapidEye, SPOT-5, Sentinel-2 and Landsat-8) in parallel with the collection of field data (leaf traits) for early bark beetle detection. The results from analysis of different spectral vegetation indices at both leaf and canopy levels under bark beetle infestation during the green-attack stage revealed that red-edge and SWIR in the optical domain were the most important spectral regions at both leaf and canopy levels for detecting subtle changes in Norway spruce trees due to bark beetle infestation. Furthermore, from the results of temporal analysis using a time series of seven RapidEye scenes and six SPOT-5 scenes in parallel with field measurements, we identified for the first time in a European situation (in contrast to earlier works in the US) that mid-June to the beginning of July is an appropriate time frame for detection of early stress induced by bark beetle infestation.
Our study furtherhighlighted the importance and potential of thermal infrared data from Landsat-8 for the early detection of bark beetle infestations and the production of reliable infestation maps at the green-attack stage.
In general, this study contributes to applied research in the field of remote sensing of bark beetle green attack. The findings and methods applied in this work can potentially be used to produce valuable information regarding bark beetle infestation at an early stage of the attack. Our findings can improve bark beetle management activities by providing useful information regarding how, when and which remote-sensing data could be applied to such survey practice, and therefore administrative bodies of forested areas may benefit from this information as an guidance for landscape-wide detection of bark beetle green attack.
