An accuracy analysis of mangrove tree height mensuration using forestry techniques, hypsometers and UAVs

Tree height is a fundamental measurement in forest inventory studies and a critical variable for the assessment of tree biomass, carbon stock and site productivity. However, measuring tree height is often a challenging task and may generate errors. This study provides an accuracy analysis of tree heights measured through different methods ranging from traditional techniques (thumb rule and stick method) to trigonometric equipment (clinometer, laser rangefinder, altimeter), and advanced technologies (Unmanned Aerial Vehicle or UAV and distometer). Along with scientific insights for the in situ application of these methods, the factors generating errors in tree height mensuration and its impact on forest biomass estimation were determined. Our results showed that the amount of error varies from one method to another. The amount of error was highest with the thumb rule and stick method (15%) while the range of error was similar for the clinometer (7.7%), laser rangefinder (7.1%) and altimeter (7.5%). Parameters such as tree form, the status of tree (i.e. if a tree was either isolated or within a canopy) and height of tree were found to significantly affect error generation during tree height measurements. Information on the extent to which biomass estimation is influenced by tree height errors associated with the use of different methods and instruments and the direction of error impact (overestimation or underestimation of biomass) are discussed. Finally, we recommend that the choice of method for tree heights in field inventory depends on certain factors such as cost, available time and manpower, required skills, site of observation and amount of error generated by each of the methods.SCOPUS: ar.j