title: Tree component biomass expansion factors and root-to-shoot ratio of Lebombo ironwood: measurement uncertainty.
abstract: BACKGROUND
  National and regional aboveground biomass (AGB) estimates are generally computed based on standing stem volume estimates from forest inventories and default biomass expansion factors (BEFs). AGB estimates are converted to estimates of belowground biomass (BGB) using default root-to-shoot ratios (R/S). Thus, BEFs and R/S are not estimated in ordinary forest inventories, which results in uncertainty in estimates of AGB and BGB. Here, we measured BEF and R/S values (including uncertainty) for different components of Lebombo ironwood (Androstachys johnsoniiPrain) trees and assessed their dependence on tree size.
  
  
  RESULTS
  The BEF values of tree components were unrelated or weakly related to tree size, and R/S was independent of tree size. BEF values varied from 0.02 for foliage to 1.31 Mg m-3for whole tree; measurement uncertainty (SE) varied from 2.9% for stem BEF to 10.6% for whole-tree BEF. The belowground, aboveground, and whole-tree BEF-based biomass densities were 30 ± 2.3 (SE = 3.89%), 121 ± 7.84 (SE = 3.23%), and 151 ± 9.87 Mg ha-1(SE = 3.27%), respectively. R/S was 0.24 with an uncertainty of 3.4%.
  
  
  CONCLUSIONS
  Based on the finding of independence or weak dependence of BEF on tree size, we concluded that, forA. johnsonii, constant component BEF values can be accurately used within the interval of harvested tree sizes.
authors: Departamento de Engenharia Florestal, Universidade Eduardo Mondlane, Campus Universitário Principal, Edifício no 1, Maputo, Mozambique ; Department of Forest and Wood Science, University of Stellenbosch, Private Bag X1 Matieland, 7602 Stellenbosch, South Africa.
authors: Tarquinio Mateus
authors: TM
authors: Magalhães
authors: Department of Forest and Wood Science, University of Stellenbosch, Private Bag X1 Matieland, 7602 Stellenbosch, South Africa.
authors: Thomas
authors: T
authors: Seifert
keywords: Additivity; Androstachys johnsonii Prain; Belowground biomass; Forest inventory; Mecrusse