Tree component biomass expansion factors and root-to-shoot ratio of Lebombo ironwood: measurement uncertainty

Abstract

BackgroundNational 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 johnsonii Prain) trees and assessed their dependence on tree size.ResultsThe 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−3 for 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%.ConclusionsBased on the finding of independence or weak dependence of BEF on tree size, we concluded that, for A. johnsonii, constant component BEF values can be accurately used within the interval of harvested tree sizes.

Live above- and belowground biomass of a Mozambican evergreen forest: a comparison of estimates based on regression equations and biomass expansion factors

“…The easternmost Mecrusse forest patches, located in Mabote, Funhalouro, Panda, Mandlakaze, and Chibuto districts, were defined as the study area and encompassed 4,502,828 ha (Dinageca 1997), of which 226,013 ha (5 %) were Mecrusse woodlands. Maps showing the area of natural occurrence of mecrusse in Inhnambane and Gaza provinces and the study area, along with detailed description of the species and the forest type can be found in Magalhães and Seifert (2015c) and Magalhães (2015).…”

“…where v hk , D hk and H hk represent stem volume, DBH and tree height of the k th tree in the h th plot, ff and BEF c represent the average Hohenadl form factor (0.4460) and tree component BEFs of A. johnsonii estimated by Magalhães and Seifert (2015c).…”

“…Nonetheless, national and regional biomass estimates are generally calculated based on BEFs (Magalhães and Seifert 2015c), especially when using national forest inventory data (Schroeder et al 1997;Tobin and Nieuwenhuis 2007). Jalkanen et al (2005) compared regression equations based and BEF-based biomass estimates for pine-, spruceand birch-dominated forests and mixed forests and concluded that BEF-based biomass estimates were lower and associated with larger error than regression equations based biomass estimates.…”

Site-specific height-diameter and stem volume equations for Lebombo-ironwood

“…This assumption is met, as this species occurs in a narrow climatic, altitudinal (Table 1) and soil conditions (Magalhães & Seifert 2015a,b, Magalhães 2015a.…”

“…The volume of the major segment was determined using Hohenadl's formula (Magalhães & Seifert 2015a), and that of the stem was computed by summing the volume of the major segment and that of the stump, computed using either Huber's or Smalian's formula, depending on the number of diameter measurements taken.…”