Peninsula, these two taxa are freely hybridized, and their taxonomy is somewhat confused, with each possessing a number of different nomenclatural identities (Castroviejo et al. 1990). Of the two taxa, Betula pubescens is the more oceanic, westerly distributed taxon while Betula pendula

The taper functions of Kozak (1988), Bi (2000) and Fang et al. (2000) were comparatively analyzed in the present paper to develop a system for calculating the merchantable volume of oaks in the northwestern region of the state of Chihuahua (Mexico). Taper data corresponding to 298 trees were collected in mixed and uneven-aged pine-oak stands located throughout the study area, and covering the existing range of ages, stand densities and sites. Results show that the compatible segmented model developed by Fang et al. (2000) best described the experimental data and is therefore recommended for estimating tree diameter at a specific height, height to a specific diameter, merchantable volume, and total volume for oaks. The equation developed in this study is a fundamental tool for use in forest surveys in the study region and is simple enough to ensure its operational implementation. The results of the statistical analysis show that the equation can be recommended for other regions, although some local adaptations may be needed.

In this paper we present a review of forest models developed in Spain in recent years for both timber and non timber production and forest dynamics (regeneration, mortality). Models developed are whole stand, size (diameter) class and individual-tree. The models developed to date have been developed using data from permanent plots, experimental sites and the National Forest Inventory. In this paper we show the different sub-models developed so far and the friendly use software. Main perspectives of forest modeling in Spain are presented.Key words: timber production; non-wood production; recruitment; modeling; forest. Resumen Modelos de crecimiento y producción en España: historia, ejemplos contemporáneos y perspectivasEn el presente trabajo se presenta una revisión sobre los modelos forestales desarrollados en España durante los úl-timos años, tanto para la producción maderable como no maderable y, para la dinámica de los bosques (regeneración, mortalidad). Se presentan modelos tanto de rodal completo como de clases diamétricas y de árbol individual. Los modelos desarrollados hasta la fecha se han desarrollado a partir de datos procedentes de parcelas permanentes, ensayos y el Inventario Forestal Nacional. En el trabajo se muestran los diferentes submodelos desarrollados hasta la fecha,

-A stand basal area growth system for radiata pine (Pinus radiata D. Don) plantations in Galicia (Northwestern Spain) was developed from data corresponding to 247 plots measured between one and five times. Six dynamic equations were considered for analysis and both numerical and graphical methods were used to compare alternative models. The equation that best described the data was a dynamic equation derived from the Korf growth function by the generalized algebraic difference approach (GADA) and by considering two parameters as site-specific. This equation was fitted in one stage by the base-age-invariant dummy variables method. The system also incorporated an equation for predicting initial stand basal area, expressed as a function of stand age, site index, and the number of trees per hectare. This information can be used to establish the starting point for the projection equation when no inventory data are available. The effect of thinning on stand basal area growth was also analyzed and the results showed that the same projection equation can be used to obtain reliable predictions of unit-area basal area development in thinned and unthinned stands. stand basal area projection / stand basal area initialization / dummy variables method / generalized algebraic difference approach / thinning effect Résumé -Modélisation de la croissance en surface terrière de plantations de Pinus radiata dans le Nord-ouest de l'Espagne. Un système d'équations modélisant la croissance en surface terrière a été développé pour des plantations de Pinus radiata D. Don en Galice (Nord-ouest de l'Espagne) à partir des données recueillies dans 247 placettes mesurées entre une et cinq fois. Six équations dynamiques ont été analysées et des méthodes graphiques et numériques ont été employées pour comparer des modèles alternatifs. Une équation dynamique dérivée de la fonction de croissance de Korf, dont les deux paramètres spécifiques à la station sont estimés par l'approche de la différence algébrique généralisée (GADA), décrit le mieux les données. L'équation a été ajustée en une seule étape en utilisant la méthode des variables indicatives indépendantes de l'âge. En outre, pour prédire la surface terrière initiale, le système incorpore aussi une fonction de l'âge du peuplement, de l'indice de fertilité de station et du nombre d'arbres à l'hectare. Cette information peut être utilisée pour fixer l'état initial de l'équation de projection quand les données d'inventaire ne sont pas disponibles. L'effet de l'éclaircie sur la croissance en surface terrière a également été analysé et les résultats montrent que la même équation de projection peut être utilisée pour prédire de façon fiable l'évolution de la surface terrière dans les peuplements non éclaircis et les peuplements éclaircis. projection de la surface terrière / initialisation de la surface terrière / méthode des variables indicatives / approche généralisée de la différence algébrique / effet de l'éclaircie

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Background: Crown fires are often intense and fast spreading and hence can have serious impacts on soil, vegetation, and wildlife habitats. Fire managers try to prevent the initiation and spread of crown fires in forested landscapes through fuel management. The minimum fuel conditions necessary to initiate and propagate crown fires are known to be strongly influenced by four stand structural variables: surface fuel load (SFL), fuel strata gap (FSG), canopy base height (CBH), and canopy bulk density (CBD). However, there is often a lack of quantitative data about these variables, especially at the landscape scale. Methods: In this study, data from 123 sample plots established in pure, even-aged, Pinus radiata and Pinus pinaster stands in northwest Spain were analyzed. In each plot, an intensive field inventory was used to characterize surface and canopy fuels load and structure, and to estimate SFL, FSG, CBH, and CBD. Equations relating these variables to Sentinel-2A (S-2A) bands and vegetation indices were obtained using two non-parametric techniques: Random Forest (RF) and Multivariate Adaptive Regression Splines (MARS). Results: According to the goodness-of-fit statistics, RF models provided the most accurate estimates, explaining more than 12%, 37%, 47%, and 31% of the observed variability in SFL, FSG, CBH, and CBD, respectively. To evaluate the performance of the four equations considered, the observed and estimated values of the four fuel variables were used separately to predict the potential type of wildfire (surface fire, passive crown fire, or active crown fire) for each plot, considering three different burning conditions (low, moderate, and extreme). The results of the confusion matrix indicated that 79.8% of the surface fires and 93.1% of the active crown fires were correctly classified; meanwhile, the highest rate of misclassification was observed for passive crown fire, with 75.6% of the samples correctly classified. Conclusions: The results highlight that the combination of medium resolution imagery and machine learning techniques may add valuable information about surface and canopy fuel variables at large scales, whereby crown fire potential and the potential type of wildfire can be classified.

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