Abstract
Biomass structure is an important feature of terrestrial vegetation. The parameters of forest biomass structure are important for forest monitoring, biomass modelling and the optimal utilization and management of forests. In this paper, we used the most comprehensive database of sample plots available to build a set of multi-dimensional regression models that describe the proportion of different live biomass fractions (i.e., the stem, branches, foliage, roots) of forest stands as a function of average stand age, density (relative stocking) and site quality for forests of the major tree species of northern Eurasia. Bootstrapping was used to determine the accuracy of the estimates and also provides the associated uncertainties in these estimates. The species-specific mean percentage errors were then calculated between the sample plot data and the model estimates, resulting in overall relative errors in the regression model of −0.6%, −1.0% and 11.6% for biomass conversion and expansion factor (BCEF), biomass expansion factor (BEF), and root-to-shoot ratio respectively. The equations were then applied to data obtained from the Russian State Forest Register (SFR) and a map of forest cover to produce spatially distributed estimators of biomass conversion and expansion factors and root-to-shoot ratios for Russian forests. The equations and the resulting maps can be used to convert growing stock volume to the components of both above-ground and below-ground live biomass. The new live biomass conversion factors can be used in different applications, in particular to substitute those that are currently used by Russia in national reporting to the UNFCCC (United Nations Framework Convention on Climate Change) and the FAO FRA (Food and Agriculture Organization’s Forest Resource Assessment), among others.
Highlights
Forest biomass is an important input to the monitoring and implementation of the United NationsSustainable Development Goals [1], providing humans with materials and renewable energy, securing carbon stocks, providing links to biodiversity and recreation, and supporting agricultural production.Biomass structure is represented by biomass expansion factors and the root-to-shoot ratio (R:S), which are important characteristics that are used to estimate biomass components based on growing stock volumes (GSV), and to quantify the inter-tree allocation of biomass
This study offers a system of equations for estimating forest stand biomass structure and biomass expansion factors for Northern Eurasia, which are more systematic and have lower uncertainties compared to the currently used values for official reporting
The results are presented in the form of spatially distributed multidimensional equations, which use as much relevant information from the forest inventory as possible and are flexible enough that they can be used for different applications
Summary
Forest biomass is an important input to the monitoring and implementation of the United Nations. Biomass structure is represented by biomass expansion factors and the root-to-shoot ratio (R:S), which are important characteristics that are used to estimate biomass components based on growing stock volumes (GSV), and to quantify the inter-tree allocation of biomass. The assessment is limited to only the aboveground live biomass of trees, e.g., in applications of remote sensing [2]. Biomass structure and its indicators are different for different tree species depending on climate and soil conditions, and they vary substantially by forest type, age, levels of productivity, and stand stocking [3,4,5]. The limited amount of relevant measurements may lead to substantial biases in the estimates of biomass structure. Substantial underestimation of root biomass by Earth system models has been reported previously by Song et al [6]
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