Harmonisation of stem volume estimates in European National Forest Inventories

Abstract

& Key message Volume predictions of sample trees are basic inputs for essential National Forest Inventory (NFI) estimates. The predicted volumes are rarely comparable among European NFIs because of country-specific dbh-thresholds and differences regarding the inclusion of the tree parts stump, stem top, and branches. Twenty-one European NFIs implemented harmonisation measures to provide consistent stem volume predictions for comparable forest resource estimates. & Context The harmonisation of forest information has become increasingly important. International programs and interest groups from the wood industry, energy, and environmental sectors require comparable information. European NFIs as primary source of forest information are well-placed to support policies and decision-making processes with harmonised estimates. & Aims The main objectives were to present the implementation of stem volume harmonisation by European NFIs, to obtain comparable growing stocks according to five reference definitions, and to compare the different results. & Methods The applied harmonisation approach identifies the deviations between country-level and common reference definitions. The deviations are minimised through country-specific bridging functions. Growing stocks were calculated from the unharmonised, and harmonised stem volume estimates and comparisons were made. This article is part of the topical collection on Forest information for bioeconomy outlooks at European level

Seeing the Trees in the World’s Forests: An Extension of the Forest Transition Concept

“…Hence, the international definition of a forest is inclusive and assumes a minimum area of 0.5 ha, with a minimum width of 20 m, a minimum ground vegetation cover of 10%, and a vegetation potential to reach a 5 m height (FAO, 2000). The definitions for growing stock are more variable, but always refer to part of aerial volume of the living trees (timber wood in the tree stem up to a given diameter limit, e. g. of 7 cm), and beyond a minimum individual diameter threshold at conventional "breast height", e. g. 10 cm at 1.30 m (Gschwantner et al, 2019), that makes these definitions much more restrictive.…”

Catering Information Needs from Global to Local Scales—Potential and Challenges with National Forest Inventories

“…Most countries have some kind of volume models, but the models may have different explanatory variables (dbh, dbh and height, or dbh, height and upper diameter) and produce volume estimates with varying accuracy. Furthermore, the functional forms of volume models vary [72].…”

“…The tree-level volume estimates also vary in the sense that different parts of the stem are included in the estimates. The bole is included in all countries, but in some countries, the growing stock volume includes also the volume of the stump, tree top (volume from bole top diameter to the tip), and even large branches [72]. The additional challenge is introduced by different definitions for the stump height and for the bole top diameter.…”

“…The reference definition developed for the volume included the stem volume above the stump, but not the branches [67]. Therefore, it is most useful for coniferous species with a clear stem, but might be less useful for broadleaved trees [72]. This may be a problem, as the branches can be utilized in the same way as the bole, and they may be important also from the greenhouse gas reporting point of view.…”

“…Therefore, a set of reference definitions rather than just one definition, allows harmonization for different purposes while preserving the information content in the national level models (Figure 2). The bridging functions to as many as five different reference volumes have been estimated [72]. The differences between the volume models developed in each country and the reference volume defined in the harmonization process can be covered by using bridging functions or generic volume models.…”