Species-specific combination and calibration between area-based and tree-based diameter distributions using airborne laser scanning

The planning of wood procurement requires reliable information about the species-specific timber assortments on which the economic value of a production forest depends. The timber assortments refer to the stem volumes of the sawlog and pulpwood fractions, specified in terms of both timber quality and allowable log dimensions, e.g., the stem diameter at breast height (dbh). We propose here an airborne laser scanning based calibration framework for generating species-specific dbh distributions that combines the area-based approach (ABA) and individual-tree detection (ITD), two established and independent approaches for retrieving forest attributes from airborne laser scanning data. Both ABA- and ITD-derived dbh distributions were generated nonparametrically for pine, spruce, coniferous, deciduous, and all species and assessed with respect to the plot-level species-specific total stem volume ([m.sup.3] x [ha.sup.-1]) and approximations of volume of timber assortments. Although after calibration, the total volume of all species and the volume approximations of coniferous sawlog and spruce pulpwood decreased in accuracy by 4%-7%, the calibration improved the accuracy of the other 12 species-specific estimates by 2%-17%, testifying to the general effectiveness of the proposed calibration framework. Key words: species specific, forest inventory, timber assortments, diameter distribution, airborne laser scanning. La planification de l'approvisionnement en bois exige des donnees fiables au sujet des assortiments de bois specifiques a l'espece dont depend la valeur economique de la production de la foret. Les assortiments de bois referent aux fractions du volume des tiges destinees au sciage et a la pate, definies tant en termes de qualite du bois que de dimension des grumes admissible, telle que le diametre de la tige a hauteur de poitrine (dhp). Nous proposons ici une approche de calibration fondee sur le balayage laser aeroporte pour generer des distributions de dhp specifiques a l'espece qui combinent une approche par zones (APZ) et la detection d'arbres individuels (DAI), deux approches eprouvees et independantes pour obtenir des attributs forestiers a partir de donnees de balayage laser aeroporte. Les deux distributions de dhp derivees de l'APZ et de la DAI ont ete generees de facon non parametrique pour le pin, l'epicea, les coniferes, les feuillus et toutes les especes et elles ont ete evaluees quant au volume total de la tige ([m.sup.3] x [ha.sup.-1]) de chaque espece a l'echelle de la place echantillon et aux approximations du volume des assortiments de bois. Bien qu'apres calibration le volume total de toutes les especes et les approximations du volume des billes de sciage des coniferes et du bois a pate d'epicea aient diminue de 4-7 %, la calibration a ameliore la precision des douze autres estimations specifiques a l'espece de 2-17 %, temoignant de l'efficacite generale de l'approche de calibration qui est proposee. [Traduit par la Redaction] Mots-cles: specifique a l'espece, inventaire forestier, assortiment de bois, distribution des diametres, balayage laser aeroporte.
1. Introduction The planning of wood procurement counts on obtaining reliable information on stand characteristics, especially the total stem volume and the timber assortments and tree species available, which markedly [...]