Improving aboveground biomass estimates by taking into account density variations between tree components

Antoine Billard,Frédéric Mothe,Fleur Longuetaud,Mathieu Jonard,Francis Colin,Rodolphe Bauer

doi:10.1007/s13595-020-00999-1

Abstract

• Key message Strong density differences were observed between stem wood at 1.30 m and other tree components (stem wood, stem bark, knots, branch stumps and branches). The difference, up to 40% depending on the component, should be taken into account when estimating the biomass available for industrial uses, mainly fuelwood and wood for chemistry. • Context Basic density is a major variable in the calculation of tree biomass. However, it is usually measured on stem wood only and at breast height.• Aims The objectives of this study were to compare basic density of stem wood at 1.30 m with other tree components and assess the impact of differences on biomass.• Methods Three softwood species were studied: Abies alba Mill., Picea abies (L.) H. Karst., Pseudotsuga menziesii (Mirb.) Franco. X-Ray computed tomography was used to measure density.• Results Large differences were observed between components. Basic density of components was little influenced by tree size and stand density. Overall, bark, knot and branch biomasses were highly underestimated by using basic density measured at 1.30 m.• Conclusion Using available wood density databases mainly based on breast height measurements would lead to important biases (up to more than 40%) on biomass estimates for some tree components. Further work is necessary to complete available databases.

Highlights

This work focuses on the estimation of tree aboveground woody biomass, by detailing the different tree components, on the basis of volume data that are widely available from national forest inventories
On average for all three species, the density values are in the following decreasing order: knots, branch insertions, branches without insertion, bark and knot-free stem wood (Fig. 3 and Appendix B to compare with the values reported in public databases in Appendix D)
Except for Ps. menziesii, the mean basic density (BD) of knots, branch insertions, branches without insertion and bark were all larger than the breast height BD that was of 407, 356 and 453 kg · m−3 for A. alba, P. abies and Ps. menziesii, respectively

Summary

Introduction

This work focuses on the estimation of tree aboveground woody biomass, by detailing the different tree components, on the basis of volume data that are widely available from national forest inventories. Such an approach based on volume and a conversion factor, here the density of the tree component, is referred to as an indirect approach (Somogyi et al 2007; Longuetaud et al 2013). It is important that the density values used are reliable and representative of the forest resource (Fearnside 1997; Sagang et al 2018)

Objectives

Methods

Results

Discussion

Conclusion