The DeLeaves: a UAV device for efficient tree canopy sampling

Abstract

Tree canopy sampling is critical in many forestry-related applications, including ecophysiology, foliar nutrient diagnostics, remote sensing model development, genetic analysis, and biodiversity monitoring and conservation. Many of these applications require foliage samples that have been exposed to full sunlight. Unfortunately, current sampling techniques are severely limited in cases where site topography (e.g., rivers, cliffs, canyons) or tree height (i.e., branches located above 10 m) make it time-consuming, expensive, and possibly hazardous to collect samples. This paper reviews the recent developments related to UAV-based tree sampling and presents the DeLeaves tool, a new device that can be installed under a small UAV to efficiently sample small branches in the uppermost canopy (i.e.,< 25 mm stem diameter,< 500 g total weight, any orientation). Four different sampling campaigns using the DeLeaves tool are presented to illustrate its real-life use in various environments. So far, the DeLeaves tool has been able to collect more than 250 samples from over 20 different species with an average sampling time of 6 min. These results demonstrate UAV-based tree sampling’s potential to greatly enhance key tasks in forestry, botany, and ecology.

On the Spatio-Temporal Under-Representation of Isotopic Data in Ecohydrological Studies

“…If robust correlations between different test trees at a particular location are developed (potentially also including water isotope values), UAV-based upscaling is a relatively simple but powerful approach. Furthermore, UAV technologies have evolved up to a point where even branch sampling from the canopy of any given tree is feasible (Charron et al, 2020). This would tremendously support the design of water isotope studies, as the user could literally "select" trees to be sampled for isotope analysis (e.g., all trees of a certain species, height, along an elevation gradient).…”

Foliar sampling with an unmanned aerial system (UAS) reveals spectral and functional trait differences within tree crowns

“…In summary, our study highlights the importance of accurately matching leaves and spectra during spectroscopic field campaigns. Twig-sampling devices operated from a UAS provide a valuable cost-and time-effective option for sampling from the top and centre of tree crowns (Charron et al 2020), which are difficult to reach with conventional sampling methods. Opportunities for imaging spectroscopy across scales are rapidly increasing (Turner 2014).…”

“…The DeLeaves sampling device consists of a grasping mechanism, a rotating saw, a branch-holding mechanism, and a camera all installed on a carbon fibre rod, as well as a custom quick-release system. It has a total mass of 1100 g and can be operated from any UAV with a maximum payload allowance of 1500 g (for details, see Charron et al 2020).…”

“…However, the very top of a tree (i.e., the crown summit) is not always reachable with standard sampling equipment such as pole pruners or line launchers. Canopy tops might be out of reach even for professional tree climbers that can operate equipment from within the crown, and more permanent infrastructures such as canopy cranes are expensive and difficult to deploy (Charron et al 2020). In addition, the degree to which the chemical and structural composition of sunlit leaves from the top and centre of tree crowns are representative for the entire canopy is not clear.…”

Extending Our Scientific Reach in Arboreal Ecosystems for Research and Management

“…New aerial sampling tools were developed by various labs with multiple actuators and a vision system to assist the operator during sample collection (Finžgar et al, 2016;Käslin et al, 2018;Kutia, 2019;Charron et al, 2020). Among the solutions available on the market, the DeLeaves canopy sampling tool (Charron et al, 2020) has now been used by scientists in a number of field experiments (NEON, 2019;Schweiger et al, 2020;Arseneau et al, 2021). This tool allows tree canopy samples to be collected in about 6 min (i.e., from UAV takeoff to return with the sample) and has proven to be effective in a variety of environments and for more than 30 tree species.…”