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In Iceland, mountain birch dominates indigenous woodlands and scrub communities. For use in inventories of the natural birch population, we derived single parameter aboveground biomass functions from a stratified random sample encompassing the entire native birch population. We evaluated the accuracy of these models on independent data from the same population and used regressions of log-transformed predicted versus observed values and compared slope and intercept parameters against the 1:1 line. We propose that the level of accuracy of allometric models might be quantified by the size of Theil’s random error component (Ue) and the normality of residual variances might be a decisive test of acceptable functions. The commonly used allometric power function without intercept proved highly accurate for diameters at ground level but was biased for diameters measured at 0.5 m up the stem. We compared both non-linear regressions and log-transformed linear regression techniques. The latter produced more accurate models especially for applications to small diameter trees. Power functions with intercept and diameters measured 0.5 m above ground produced accurate estimates, except for trees with diameters less than 50 mm. We suggest allometric models for general use in Iceland for inventories of native birch woodlands and scrub, Á Íslandi er birki ríkjandi trjátegund í náttúrulegu skóg- og kjarrlendi. Við settum fram lífmassaföll fyrir birki sem byggja á lagskiptu slembiúrtaki úr öllum birkiskógum landsins. Við mátum áreiðanleika fallanna með öðru gagnasafni úr skógunum. Tekin var náttúrulegur lógarytmi af raungildum og spágildum og síðan fundið línulegt fall milli þeirra. Skurðpunktur og halli línunnar var borinn saman við línu úr upphafspunkti með hallatölu einn. Við mátum skekkju í föllunum út frá hlutdeild tilviljanakenndra frávika af óskýrðum breytileika (Theil’s Ue) og normaldreifingu frávika. Einfalt veldisfall reyndist mjög áreiðanlegt þegar þvermál er mælt við jörðu en föll fyrir þvermál 0.5 m frá jörðu reyndust gefa skekkt gildi. Við bárum saman aðferðir með ólínulegu aðhvarfi lífmassa að þvermáli og línulegu aðhvarfi náttúrulegs lógaritma að þvermáli. Seinni aðferðin reyndist gefa betri spálíkön einkum fyrir grennri tré. Veldisföll með upphafsfasta sem felld eru að þvermáli 0,5 m yfir jörðu reyndust óskekkt fyrir tré með sverari en 50 mm stofn í 0,5 m hæð. Að lokum bentum við á bestu föllin til að áætla lífmassa ofanjarðar í úttektum á Íslenskum birkiskógum.

Key message This analysis of the tools and methods currently in use for reporting woody biomass availability in 21 European countries has shown that most countries use, or are developing, National Forest Inventory-oriented models whereas the others use standwise forest inventory--oriented methods. Context Knowledge of realistic and sustainable wood availability in Europe is highly relevant to define climate change mitigation strategies at national and European level, to support the development of realistic targets for increased use of renewable energy sources and of industry wood. Future scenarios at European level highlight a deficit of domestic wood supply compared to wood consumption, and some European countries state they are harvesting above the increment. Aims Several country-level studies on wood availability have been performed for international reporting. However, it remains essential to improve the knowledge on the projection methods used across Europe to better evaluate forecasts. Methods Analysis was based on descriptions supplied by the national correspondentsinvolved in USEWOOD COST Action (FP1001), and further enriched with additionaldata from international reports that allowedcharacterisation of the forests in these countries for the same base year. Results Methods currently used for projecting wood availability were described for 21 European countries. Projection systems based on National Forest Inventory (NFI) data prevail over methods based on forest management plans. Only a few countries lack nationwide projection tools, still using tools developed for specific areas. Conclusions A wide range of NFI-based systems for projecting wood availability exists, being under permanent improvement. The validation of projection forecasts and the inclusion of climate sensitive growth models into these tools are common aims for most countries. Cooperation among countries would result in higher efficiency when developing and improving projection tools and better comparability among them. © 2016, INRA and Springer-Verlag France.

The supply of wood in Europe on a sustainable basis is highly relevant for forestry and related policies, particularly in relation to (i) analysing global change mitigation strategies and carbon accounting (ii) establishing realistic forecasts and targets for wood resources, biomass and renewable energy and (iii) assessing and supporting strategies for an increased use of wood. Therefore, it is relevant to have robust information of the availability for wood supply. The main aim of this paper is to harmonize the concept of ‘forest available for wood supply’ (FAWS) at European level. The data employed in this study was acquired through two questionnaires. The first questionnaire, conducted under the framework of COST Action FP1001 and a second questionnaire was completed by national correspondents and members of the UNECE/FAO. The analysis showed that reasons for the exclusion of forest from FAWS are diverse. Legal restrictions and specifically ´Protected areas´ are considered by 79% of the countries while very few countries consider economic restrictions. A new FAWS reference definition is provided and the consequences of using this new definition in eight European countries were analysed. Application of the proposed definition will increase consistency and comparability of data on FAWS and will result in decreasing the area of FAWS at a European level.