Marcos Barrio-Anta

Effects of foliar nutrients and environmental factors on site productivity in Pinus pinaster Ait. stands in Asturias (NW Spain)

Abstract• BackgroundThe effects of foliar nutrients and environmental variables on site productivity in Maritime pine (Pinus pinaster Ait.) stands in Asturias (NW Spain) were studied.• MethodsSite productivity was evaluated by means of site index. The environmental characteristics considered included physiographic, edaphic and climatic variables. Two different statistical analyses were carried out to determine the key factors affecting site productivity: the CHAID procedure and parametric regression techniques.• ResultsThe regression trees obtained by applying the CHAID algorithm separately to each type of variable revealed the order of importance of the environmental factors. In addition, the variables corresponding to the first level of branches of the CHAID regression trees were consistent with those identified by parametric regression. According to the parametric regression model, a physical soil characteristic (soil depth) and a climatic characteristic (mean summer temperature) were the most important variables for explaining site productivity in the region. Foliar concentrations of phosphorus and elevation were not significant factors in the parametric regression analysis (although considered key factors when foliar nutrients and physiographic variables were analyzed separately).• ConclusionAlthough the percentage variability in SI explained by the best parametric model was not very high (45%), the model is parsimonious and provides robust estimates of the spatial distribution of this variable. The results obtained provide further information about the ecology of this species in Asturias, and represent an important tool in forest management, especially for afforested areas.

Aboveground stand-level biomass estimation: a comparison of two methods for major forest species in northwest Spain

ContextThe scaling-up approach (which requires the use of individual tree biomass equations and data) is one of the most commonly used methods for estimating stand biomass at a local scale. However, biomass prediction over large management areas requires more efficient methods.AimsTwo methods of estimating aboveground stand biomass were developed and compared: stand biomass equations (SBE) including observed stand variables, and SBE including biomass expansion factors (BEF) and stand volume.MethodsTwo types of systems of additive equations were fitted simultaneously for components and total aboveground stand biomass, to ensure additivity. Inherent correlations among biomass components were also taken into account in the fitting process.ResultsThe systems explained a high percentage of the observed variability. The SBE systems that included observed stand variables provided more accurate estimates than those that included BEF and stand volume. However, the latter were found to be more precise for stem wood and total aboveground biomass prediction.ConclusionsBoth approaches provide a direct link between forest inventory data, outputs from whole-stand growth models, and biomass estimates at stand level. Taking into account that the inventory effort is similar for both alternatives, the choice of which to use will depend on the data available and on the relative importance of the biomass components for the end-users.

Modelling stand basal area growth for radiata pine plantations in Northwestern Spain using the GADA

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.RésuméUn 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.

Using density management diagrams to assess crown fire potential in Pinus pinaster Ait. stands

ContextDensity management diagrams (DMDs) are useful for designing, displaying and evaluating alternative density management regimes for a given stand-level management objective. The inclusion of variables related to crown fire potential within DMDs has not previously been considered.AimsThe aim of this study was to include isolines of variables related to crown fire initiation and spread in DMDs to enable identification of stand structures associated with different types of wildfire.MethodsBiometric and fuel data from maritime pine (Pinus pinaster Ait.) stands in NW Spain were used to construct DMDs. Different surface and crown fire behaviour models were used together to estimate crown fire potential.ResultsThe crown fire potential varied greatly throughout development of the maritime pine stands. Low stands were more prone to crowning. The type of crown fire was mainly determined by stand density.ConclusionThe DMDs developed can be used to identify relationships between stand structure and crown fire potential, thus enabling the design of thinning schedules aimed at reducing the likelihood of crowning.

Developing a dynamic growth model for maritime pine in Asturias (NW Spain): comparison with nearby regions

Abstract∙ Key messageA dynamic growth model was developed for maritime pine in Asturias. During the evaluation process, a stand volume ratio function proved the best of two alternative methods for estimating merchantable volume. Comparison of the developed model with existing models for nearby regions showed that a single model may suffice for the whole of the NW Iberian Peninsula.∙ ContextMaritime pine is one of the most important tree species in NW Spain. There was no existing dynamic growth model for this species in Asturias.∙ AimsTo develop a dynamic growth model for maritime pine in Asturias, by evaluating two different methods of estimating volume (a disaggregation system and a stand volume ratio function), and to compare the developed model with existing models for Galicia and northern Portugal are the goals of this study.∙ MethodsThe dynamic model is based on the state-space approach, in which three state variables characterize the stand at any point in time: dominant height, number of stems per hectare and stand basal area. The transition function for the first variable was developed on the basis of stem analysis data in a previous study, while the corresponding functions for the last two variables were simultaneously fitted with data obtained from successive measurements of permanent plots. An appendix outlining the implementation of a stand growth simulator in the R environment is included to facilitate model use and evaluation.∙ ResultsWhen the whole model was used to project the stand conditions, the stand volume ratio function performed best, yielding a root mean square error of 22.4 m3 ha−1 and a critical error of 18.4 %. Comparison with models developed for other regions revealed both similarities and differences, some of which may be attributed to an unequal distribution of the available data in age and site quality classes.∙ ConclusionThe proposed dynamic growth model provided accurate results, and comparison with other region-specific models showed that a single dynamic model may suffice for the whole of the NW Iberian Peninsula.

Evaluation of age-independent methods of estimating site index and predicting height growth: a case study for maritime pine in Asturias (NW Spain)

Site index is the most common measure of forest site productivity used worldwide, serving as an important baseline for forest-level planning and helping to formulate silviculture strategies. Site index is usually obtained through measurement of dominant height and stand age. However, age is not available in many cases, such as in most national forest inventories or when it is not a main determinant of growth. Age-independent methods have been developed to overcome this problem, allowing modelling of the dominant height growth and estimation of site index in the absence of age data. The purpose of this study was to compare the most widely used age-dependent method and several age-independent alternatives, namely the growth intercept method, the age-independent difference equation method and an iterative method proposed in this study. We used stem analysis and permanent sample plot data from Pinus pinaster Ait. stands in Asturias, Spain, to test the alternative methods. It was found that for site index estimation, a 7-year growth intercept was the most accurate method. However, for prediction of dominant height growth, an age-independent equation that depends on climatic factors performed best, even better than the traditional age-dependent site quality curves. The iterative method proposed in this study proved to be the least accurate alternative, although it performed well in predicting height growth for long intervals starting from low heights. Finally, we provide recommendations regarding when the different methods should be used.

Potential Above Ground Biomass Production and Total Tree Carbon Sequestration in the Major Forest Species in NW Spain

SUMMARY Potential biomass production and carbon sequestration were studied in relation to different site index conditions, stand densities and silvicultural treatments for the main forest species in northwest Spain. Site quality, stand density and silvicultural treatments affected biomass production and carbon sequestration and, therefore, optimal rotation length. Potential biomass production and carbon sequestration were highest and optimal rotations were shortest for the best site indexes, highest initial stand densities and the silvicultural treatments that involved least disturbance. Fast-growing species can be used as both energy crops (biomass) and carbon sinks, which contribute to mitigating climate change. However, as slow-growing species act as sinks for longer, they are preferable for planting in environments that are less suitable for fast-growing species.