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Nation-wide Sentinel-2 mosaics were used with National Forest Inventory (NFI) plot data for modelling and subsequent mapping of spruce-, pine-, and deciduous-dominated forest in Norway at a 16 m * 16 m resolution. The accuracies of the best model ranged between 74% for spruce and 87% for deciduous forest. An overall accuracy of 90% was found on stand level using independent data from more than 42 000 stands. Errors mostly resulting from a forest mask reduced the model accuracies by ~10%. The produced map was subsequently used to generate model-assisted (MA) and post stratified (PS) estimates of species-specific forest area. At the national level, efficiencies of the estimates increased by 20% to 50% for MA and up to 90% for PS. Greater minimum numbers of observations constrained the use of PS. For MA estimates of municipalities, efficiencies improved by up to a factor of 8 but were sometimes also less than 1. PS estimates were always equally as or more precise than direct and MA estimates but were applicable in fewer municipalities. The tree species prediction map is part of the Norwegian forest resource map and is used, among others, to improve maps of other variables of interest such as timber volume and biomass. Key words: National Forest Inventory, model-assisted estimation, poststratification, machine learning, small area estimation., Resume : Des mosaiques Sentinel-2 a l'echelle nationale ont ete utilisees avec des donnees de parcelles de l'inventaire forestier national (IFN) pour la modelisation et, par la suite, pour la [...]

Forest structure reflects the forest disturbance regime and can provide important information about the rate of human impact. A better understanding of the structural variability and large-scale dynamics of natural forests is crucial for 'close to nature' forest management planning. In this study, we developed a partly automated approach to assess the structure of potential primeval and managed beech forests in the Ukrainian Carpathians using WorldView-2 imagery. We analyzed the local (50 m x 50 m scale) canopy closure of these forests by extracting the canopy gaps and determined four forest structure types ranging from very closed to low density. The occurrence and frequencies of these structure types were significantly different in the primeval and managed beech forests. The four forest structure types were predicted and mapped using multinomial logistic regression based on the textural features derived from the original image bands and two vegetation indices. A 10-fold crossvalidation resulted in an overall accuracy of 83% and a kappa coefficient of 75%, with the highest agreement for the very closed structure type (87%) and the lowest agreement for the medium density and low density structure types (79%). The forest structure type maps can be helpful for planning management activities in beech forests. Key words: beech forests, structure types, canopy gap fraction, WorldView-2, Carpathian region. La structure forestiere reflete le regime de perturbation de la foret et peut fournir d'importantes informations au sujet du taux d'impact humain. Il est crucial d'avoir une meilleure comprehension de la variabilite structurale et de la dynamique a grande echelle des forets naturelles pour planifier une sylviculture dite ecologique. Dans cette etude, nous avons developpe une approche partiellement automatisee pour evaluer la structure des hetraies possiblement vierges ou amenagees dans les Carpates ukrainiennes a l'aide d'images du satellite WorldView-2. Nous avons analyse la fermeture du couvert forestier localement (echelle de 50 m x 50 m) en faisant abstraction des trouees dans le couvert et en determinant quatre types de structures forestieres allant de tres fermee a faible densite. L'occurrence et la frequence de ces types de structures etaient significativement differentes dans les hetraies vierges et amenagees. Les quatre types de structures forestieres ont ete predits et cartographies a l'aide de la regression logistique multinomiale sur la base des caracteristiques texturales derivees des bandes d'images originales et de deux indices de vegetation. Une validation croisee repetee a 10 fois a donne une precision globale de 83 % et un coefficient kappa de 75 %; la structure la plus fermee avait le taux de concordance le plus eleve (87 %) et les structures de densites moyenne et faible avait le taux de concordance le plus faible (79 %). Les cartes illustrant les types de structures forestieres peuvent etre utiles pour planifier les travaux sylvicoles dans les hetraies. [Traduit par la Redaction] Mots-cles: hetraies, types de structures, fraction de trouee, WorldView-2, region des Carpates., 1. Introduction Beech forests are a potentially natural vegetation type in European temperate forests and one of the dominant forest ecosystems in the Carpathian mountain region. In the Ukrainian Carpathians, [...]

Current technical advances in the field of digital photogrammetry demonstrate the great potential of automatic image matching for deriving dense surface measurements of the forest canopy. In contrast to airborne laser scanning (ALS), aerial stereo images are updated more regularly by national or regional mapping agencies in several countries. Frequently, ALS-based terrain models (DTMs) are available, and thus photogrammetric canopy heights can be derived. However, currently, there is little knowledge as to how accurately forest attributes can be modeled using the aerial stereo images acquired by these official, regular aerial surveys, especially for mixed forests in central Europe. Thus, a photogrammetric point cloud derived from UltraCamX stereo images in combination with an ALS-DTM and a classification of coniferous and deciduous tree regions (based on ortho-images) was used to create a stratified estimation of timber volume and basal area in a mixed forest in Germany. Suitable models were derived at the plot level using explanatory variables from the photogrammetric point cloud (which was normalized using an ALS-DTM). The prior stratification of conifer- and deciduous-dominated field plots slightly improved the estimation accuracy. The results verify that stereo images can be an alternative to ALS data for modeling key forest attributes, even in mixed central European forests with complex structure. Resume: Les avancees technologiques actuelles dans le domaine de la photogrammetrie numerique demontrent le fort potentiel du recalage automatique d'images pour deriver des mesures de la surface dense du couvert forestier. Contrairement au balayage laser aeroporte (BLA), les images stereoscopiques aeriennes sont mises a jour plus regulierement par des organismes nationaux ou regionaux de cartographie dans plusieurs pays. Les modeles numeriques de terrain fondes sur le BLA (MNT-BLA) sont souvent disponibles et les hauteurs photogrammetriques du couvert forestier peuvent etre ainsi derivees. Toutefois, il existe actuellement peu de connaissances quant a la precision des attributs forestiers pouvant etre modelises a l'aide d'images stereoscopiques aeriennes acquises regulierement par ces releves aeriens officiels, en particulier pour les forets melangees de l'Europe centrale. Ainsi, un nuage photogrammetrique de points (derive d'images stereoscopiques UltraCamX), combine a un MNT-BLA et une classification des regions occupees par des coniferes ou des feuillus etablie a l'aide d'orthoimages, a ete utilise pour obtenir une estimation stratifiee du volume de bois et de la surface terriere dans une foret melangee en Allemagne. Des modeles appropries ont ete obtenus a l'echelle de la placette a l'aide de variables explicatives tirees du nuage photogramme-trique de points qui avait ete normalise a l'aide du MNT-BLA. La stratification a priori des placettes dominees par des coniferes ou par des feuillus a legerement ameliore la precision de l'estimation. Les resultats confirment que les images stereoscopiques peuvent remplacer les donnees obtenues par BLA pour modeliser les attributs cles de la foret, meme dans les forets melangees a structure complexe de l'Europe centrale. [Traduit par la Redaction], Introduction The requirements for national and regional forest inventories have changed in recent decades, along with the methods of data acquisition involved. Timber volume and basal area are forest attributes [...]