The effectiveness of a method that uses stabilized cameras and photogrammetry to survey the size and distribution of individual trees in a mangrove forest

Abstract

ABSTRACT For the conservation of mangrove forests, management plans should be prepared after evaluating the decreases of mangrove forests explicitly. Although information regarding stand development in mangrove forests is indispensable, there is a lack of it. We reasoned that gathering three-dimensional point cloud data using stabilized cameras and photogrammetry (developed together with unmanned aerial vehicles) could be used to conduct a survey of the sizes and spatial distribution of individual trees in mangrove forests. We surveyed two mangrove forests growing at the mouth of the Okukubi and Ōura rivers on Okinawa Island. The forest floor was photographed using a GoPro Hero 4 attached to a camera stabilizer on about 2- m- long extension pole. The resulting images were processed with a photogrammetry software to create an orthomosaic image. The trunks of trees and seedlings in all plots were visually interpreted. The total number of the seedlings and trees in each plot was counted, and the density in each plot was calculated. The diameter at breast height (DBH) of the trees was calculated from the area of the polygons drawn around the trunks manually. There was a strong correlation between the interpreted and measured DBH. We confirmed the effectiveness of a method that uses stabilized cameras and photogrammetry to survey the size and distribution of individual trees in a mangrove forest. The information obtained by present study is considered to be an essential forest inventory of mangrove forests.