Abstract
Biophysical and biochemical traits of foliage and twigs at the top of tree canopies provide essential information on trees’ ecophysiology. Conventional methods used for canopy sampling are typically time consuming and costly, while the very canopy tops are still out of reach unless a canopy crane is used. Thus, we developed a novel twig sampling method using a device attached to a drone that allows to grasp and cut small twigs and bring them to the ground for immediate analysis. This ``Flying Tree Top Sampler'' (FTTS) complements existing methods used in tree canopy research. This paper describes the method to make it openly available to interested users, provides the necessary technical details, and reports on a proof-of-concept application by probing a single tree during senescence. In this demonstration example we show that the ability to investigate the top part of the tree leads to the clear finding that chlorophyll content of the top leaves is significantly lower than that of leaves in the lower canopy. Without the samples collected by the FTTS, the decrease of chlorophyll content with height would not have been of statistical significance using a p = 0.05 significance threshold. Besides its advantages, the existing limitations of the FTTS are discussed, and suggestions for future developments are provided.
Highlights
Forest canopies play an important role globally in terms of biodiversity, biospheric–atmospheric gas exchange, and ecosystem services (Brockerhoff et al, 2017)
The drone is controlled by a remote control (Turnigy, TGY-i10, 2.4 GHz, 10 channel, Hong Kong, China) equipped with a First Person View (FPV) system (camera: Aomway, 1200 TVL; lens: 2.8 mm; field of view: 120◦, charge-coupled device (CCD) sensor: 1/3′′ Sony HD, 22 g, Shenzen, China; transmitter: Fatshark, FSV2462, Shenzen, China; receiver: Boscam, FP632, 5.8 GHz, 40 channel, Shenzen, China) to ease the flying and sampling process for the two operators
We present a case study in which we sampled a tree growing in an allée (Norway maple, Acer platanoides L.) near the CH-CHA Swiss FluxNet site, Switzerland (47◦12′36.8′′ N, 8◦24′37.6′′ E, 393 m a.s.l.) in October 2016 during early senescence and determined leaf chlorophyll contents from a subsample of leaves from each twig collected (Figure 2)
Summary
Forest canopies play an important role globally in terms of biodiversity, biospheric–atmospheric gas exchange, and ecosystem services (Brockerhoff et al, 2017). We report on a novel, cost efficient device attached to a drone, the Flying Tree Top Sampler (FTTS). It grasps and cuts twigs (and small branches) from the very canopy top and safely carries them back to the operators. Smaller trees have been sampled with ladders, extendable tree pruners, or hydraulic forklifts, to name just a few These methods have disadvantages in both applicability to tall tree canopies, tree accessibility and difficult terrain, in particular for reaching top canopy twigs of trees within dense stands. This paper describes the method to make it openly available to interested users, provides the necessary technical details, and reports on a proof-of-concept application by probing a single tree during senescence
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