Estimating crown biomass of Oak trees using terrestrial photogrammetry in Zagros forests

Abstract

Accurate methods for biomass estimation is necessary for numerous topics related to global warming. Amongst different component of trees, crown biomass is the most difficult to measure. In this study, we tested a simple approach using a hand-held consumer grade camera to estimate the biomass of different components of crown including large and small branches and leaves. Two perpendicular images were taken from 36 Oak trees and the trees were cut down and fresh weight of components was measured in the field. Biomass was calculated for each component by multiplying fresh weight and density of each component. For the estimation of biomass using terrestrial photogrammetric method, pixels of each component were separated and used as predictor in regression equations. Biomass of each component were estimated and bias and RMSE were calculated. Based on the result, this approach provided the most accurate results for medium size trees. In general, the bias and RMSE of total crown biomass estimation were 1.45 and 4.64, respectively. Also, the accuracy of biomass estimation of large branches was the highest while that of leaves biomass was the lowest. However, the density of the stands and the size of trees are two important factors that limit the applicability of this approach.