Assessment of bud flush and damage in young Norway Spruce trees through airborne high-resolution multispectral images

Scandinavia is facing climate changes with a predicted increase in mean temperature of 2-4°C. For Swedish forests to be adapted to this challenge, the Swedish tree breeding program aims to select trees that are adapted to different biotic and abiotic conditions. Information on spring phenology, damage and vitality are important variables in the Norway spruce selection process. Traditionally, the data is gathered through manual assessment of each tree, which requires significant resources and limits the number and frequency of variables that can be measured. As an alternative, Remote Sensing is a promising technology to evaluate bud flush and vitality in conifers, offering the advantage of scoring more trees in a shorter time with fewer resources while obtaining data for several time points during the vegetation season, and its use of algorithms to measure variables reduces the risk of human error.

This project aims to develop methods that can be used within the breeding program by collecting information on spring phenology, damage and vitality using high-resolution multispectral drone images of young Norway spruce trees. Data were collected during spring 2023 and 2024. Bud flush is estimated from the spectral values of the tree crowns using manual assessment of the flush in a subset of the trees as training data. The high-resolution multispectral images will also be used to assess the damage and vitality of the new shoots. To ensure capturing the bud flush at a high temporal resolution, images were taken before the vegetation season and up to twice weekly during the period with the most rapid flush. In the final step, the spatial pattern within the study sites will be analyzed and connected to damage and vitality of the young Norway Spruce trees.