Colloquium

Exploring the Relationship Between Tree Stem Spatial Distribution and Water Stress Levels Using UAV Remote Sensing Indices

Organised by Laboratory of Geo-information Science and Remote Sensing
Date

Wed 15 January 2025 10:45 to 11:15

Venue Gaia, building number 101
Droevendaalsesteeg 3
101
6708 PB Wageningen
+31 (0) 317 - 48 17 00
Room 2

By Wouter Lammes

Abstract
Climate models forecast a rise in the frequency, intensity and duration of droughts, which will lead to more water stress at trees. Understanding the interplay between trees in the context of water stress can provide valuable insights for making informed forest management decisions. This study aims to discover how the spatial arrangement of tree stems influences tree water stress levels. This is done by using Unoccupied Aerial Vehicles (UAV)) derived imagery and Terrestrial Laser Scanning derived data for a Douglas fir dominated plot in the Zwolse Bos, The Netherlands. A Voronoi diagram is created using stem locations, and its cells are filled with corresponding Photochemical Reflectance Index (PRI) and Normalized Difference Vegetation Index (NDVI) values of the canopy. A negative Pearson correlation has been found between the cell size and PRI/NDVI with an average R of -0.273 for the PRI and -0.473 for the NDVI. Showing that in general less competition of trees lead to more water stress. A clear diurnal pattern hasn’t been found in this study. The data shows a right-skewed distribution, with 14 outliers among 150 cells. When the outliers are excluded, the Pearson correlation becomes considerably weaker but consistently remains negative. Recommendations for further research include comparing clumped and non-clumped trees to take the effect of shadow into account.