Biomass models to estimate carbon stocks for hardwood tree species

Abstract

To estimate forest carbon pools from forest inventories it is necessary to have biomass models or biomass expansion factors. In this study, tree biomass models were developed for the main hardwood forest species in Spain: Alnus glutinosa, Castanea sativa, Ceratonia siliqua, Eucalyptus globulus, Fagus sylvatica, Fraxinus angustifolia, Olea europaea var. sylvestris, Populus x euramericana, Quercus canariensis, Quercus faginea, Quercus ilex, Quercus pyrenaica and Quercus suber. Different tree biomass components were considered: stem with bark, branches of different sizes, above and belowground biomass. For each species, a system of equations was fitted using seemingly unrelated regression, fulfilling the additivity property between biomass components. Diameter and total height were explored as independent variables. All models included tree diameter whereas for the majority of species, total height was only considered in the stem biomass models and in some of the branch models. The comparison of the new biomass models with previous models fitted separately for each tree component indicated an improvement in the accuracy of the models. A mean reduction of 20% in the root mean square error and a mean increase in the model efficiency of 7% in comparison with recently published models. So, the fitted models allow estimating more accurately the biomass stock in hardwood species from the Spanish National Forest Inventory data.Key words: aboveground biomass; belowground biomass; additivity; carbon sequestration; hardwood species; biomass models. ResumenEcuaciones para la estimación de biomasa de frondosas en España Para realizar estimaciones de cantidades de carbono acumulado por los bosques, a partir de datos procedentes de inventarios forestales, es necesario disponer de modelos de estimación de biomasa o de factores de expansión. En este trabajo se han ajustado modelos de estimación de biomasa para las principales especies forestales de frondosas existentes en los bosques españoles: Alnus glutinosa, Castanea sativa, Ceratonia siliqua, Eucalyptus globulus, Fagus sylvatica, Fraxinus angustifolia, Olea europea var. sylvestris, Populus x euramericana, Quercus canariensis, Quercus faginea, Quercus ilex, Quercus pyrenaica y Quercus suber. Se han determinado las siguientes fracciones: fuste con corteza, ramas de diferentes tamaños, parte aérea y parte radical. Para cada especie se ajustó un sistema de ecuaciones utilizando la metodología de mínimos cuadrados generalizados conjuntos, que contempla el cumplimiento de la propiedad aditiva entre fracciones. Como variables independientes se utilizaron el diámetro y la altura total del árbol. El diámetro aparece en todos los modelos, no así la altura, si bien su inclusión resulta en una mejora de las estimaciones en los modelos de biomasa de fuste para la mayoría de las especies y en parte de los modelos de ramas. La comparación con otros modelos desarrollados anteriormente para estas especies y ajustados con otra metodología, indica una mejora en la precisión de los aquí p...

Decline in holm oak coppices (Quercus ilex L. subsp. ballota (Desf.) Samp.): biometric and physiological interpretations

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