“…With the recent development of drone technologies and their application in ecological studies, this might change. Drones equipped with optical detectors such as cameras capturing specific light wave lengths or laser-based approaches offer new opportunities for crown and canopy assessments (Barnes et al, 2017;Díaz-Varela, de la Rosa, León, & Zarco-Tejada, 2015;Thiel & Schmullius, 2016). Crown variables such as crown length (Kallimani, 2016), crown diameter (Lim et al, 2015;Panagiotidis, Abdollahnejad, Surový, & Chiteculo, 2016), or crown volume (Torres-Sánchez, López-Granados, Serrano, Arquero, & Peña, 2015) were calculated using photogrammetric techniques.…”