Estimating carbon storage in an old olive tree grove: A comparison of UAV, LiDAR, and manual surveys

The olive groves, particularly the old ones, represent a significant carbon sink and so they are important for climate change mitigation. Also, many of these olive groves represent an important component of the landscape heritage. This study focuses on estimating biomass and carbon content in old olive tree groves, with a specific application in a 69-year-old olive grove in central Italy. The research used UAV (Unmanned Aerial Vehicle) survey data to evaluate the geometric features of some selected olive trees, using LiDAR (Light Detection and Ranging) and manual survey as basis for comparison and benchmark. The aim was to determine the effectiveness of UAV method, which this study showed to be less costly, less time-consuming, and less prone to drawbacks compared to the LiDAR and manual measurements. After felling the olive trees, their epigeal biomass was weighed. A strong linear correlation was found between the geometric parameters (trunk circumference, crown area, and crown volume) and the fresh weight of the trees. The results of this study show that UAV surveying provides a viable solution for assessing the carbon content of old olive groves, representing a significant improvement in relation to the methods still proposed by the IPCC (Intergovernmental Panel on Climate Change). As with all other proposed methods, the main issue concerns the estimation of the belowground biomass, for which there are currently no methods with a low degree of uncertainty, so there is a need to develop more accurate models.