Detailed mapping of below canopy surface temperatures in forests reveals new perspectives on microclimatic processes

Abstract

The microclimate within forest stands might change rapidly in space and time due to the complex three-dimensional structure of forests. We are nowadays able to map the structure of forest stands in high detail, due to advances in Light Detection and Ranging (LiDAR) technologies such as terrestrial laser scanning (TLS). But measurements of microclimatic properties are often still bound to sensors which are only able to provide point measurements. Therefore, we propose a novel method to map the surface temperatures of a mature forest stand based on sensor fusion of TLS and thermal imaging as a time series. We provide insights into small scale temperature changes like sun flecks, or different bark structures. The results were also indicative of a cooling effect on tree trunks due to the uptake of cooler soil water, which is directly linked to the sap flux within the tree. While being only a first proof of concept of this method, our study provides a successful characterisation of spatio-temporal dynamics in trunk temperatures and indicates a potential promising correlation with ecohydrological processes. Our results suggest this novel technology to open various opportunities for future research and ecosystem monitoring.