Anton Kunneke, Jan van Aardt, Wesley Roberts, and Thomas Seifert

2.1 Introduction

The aim of this chapter is to provide an overview of methods of estimating woody biomass from inventory information.

In understanding any resource, the extent (spatial localisation) as well as the amount of resource should be estimated. Inventory is the term used in forestry practice for assessing the timber resource. The result of an inventory should establish at least three values. The first is the estimated mass or volume of resource per unit area, for a given time period, the second value is the total area of the resource, and the third is an error value (accuracy and precision) associated with the estimate. In a heterogeneous resource a subdivision of the resource in classes is also necessary. Common subclasses could be vegetation types (e. g., 0-30 % tree cover, 30-50 % tree cover, broadleaved forest and savannah, etc.) or qualitative age classes (e. g., young, semi mature, mature). For instance, naturally regenerated forests, as opposed to commercial plantations, contain all age classes in a single stand at the same time. An inventory in those forests will therefore provide a range of diameter classes, and should rather concentrate on size than age.

Conventional forest inventory typically attempts to establish the volume of utilisable wood or bio-energy in the forest stand. The minimum information necessary for bio-energy use is a map with the available biomass and a value in

A. Kunneke (H) • T. Seifert

Department of Forest and Wood Science, Stellenbosch University, Stellenbosch, South Africa e-mail: ak3@sun. ac. za

J. van Aardt

Centre for Imaging Science, Digital Imaging and Remote Sensing Group,

Rochester Institute of Technology, Rochester, NY, USA

W. Roberts

BioCarbon Partners, Cape Town, South Africa

T. Seifert (ed.), Bioenergy from Wood: Sustainable Production in the Tropics, Managing Forest Ecosystems 26, DOI 10.1007/978-94-007-7448-3__2,

© Springer Science+Business Media Dordrecht 2014 kg m“2 for each section (stand or subdivision) on the map, since the localisation of the biomass will guide all further steps of harvesting (Chap. 6). Biofuel can be described by characteristics such as energy content (MJ kg_1) and heating value (MWh kg_1). Furthermore, it might be desirable to know the percentage of components of biomass, e. g., leaves, twigs, branches, bark and stem wood, since the comprehensive biomass composition determines the ash content, a critical factor in bio-energy conversion (Chaps. 7 and 9) and is a major determinant for the export of nutrients and thus stand sustainability (Chap. 10). Models that estimate biomass composition, based on inventory data, are thus relevant additions to the typical inventory information (Chap. 3). Biomass resource assessment or inventory is in essence then no different from conventional inventory in that the quantity and quality of biomass needs to be estimated. It differs in that the mass and not the volume has to be estimated and that the quality parameters differ. This chapter will concentrate on procedures to estimate the mass and quality parameters needed, while briefly hinting at the associated errors associated with these.

Three main approaches could be followed to provide biomass assessments:

• Sample plot-based methods using terrestrial light detection and ranging (LiDAR) scans (TLS) or standard methods, as with conventional timber inventory, related to diameter and height measurements in sample plots. The sample plots are assumed to be representative of the area in the inventory and models are used to predict the component fractions of the stand in the inventory.

• Aerial surveys based on LiDAR and photogrammetry estimates of tree param­eters (number, height, crown size, etc.) at the stand level, applied to models to predict total biomass and biomass components of the stand.

• Space or aerial survey methods of estimating total aboveground biomass directly. This is possible with SAR and LiDAR methods, as well as optical infrared sensing in combination with models. The total aboveground mass is a single value, which requires additional modelling to predict a breakdown of component fractions for the stand.

This chapter will describe the methods used in measuring parameters, while the upscaling and modelling of component fractions will be dealt with in Chap. 3.