Abstract
Quantifying the carbon balance in forests is one of the main challenges in forest management. Forest carbon stocks are usually estimated indirectly through biomass equations applied to forest inventories, frequently considering different tree biomass components. The aim of this study is to develop systems of equations for predicting tree biomass components for the main forest softwood species in Spain: Abies alba Mill., A. pinsapo Boiss., Juniperus thurifera L., Pinus canariensis Sweet ex Spreng., P. halepensis Mill., P. nigra Arn., P. pinaster Ait., P. pinea L., P. sylvestris L., P. uncinata Mill. For each species, a system of additive biomass models was fitted using seemingly unrelated regression. Diameter at the breast height and total height were used as independent variables. Diameter appears in all component models, while tree height was included in the stem component model of all species and in some branch component equations. Total height was included in order to improve biomass estimations at different sites. These biomass models were compared to previously available equations in order to test their accuracy and it was found that they yielded better fitting statistics in all cases. Moreover, the models fulfil the additivity property. We also developed root:shoot ratios in order to determine the partitioning into aboveground and belowground biomass. A number of differences were found between species, with a minimum of 0.183 for A. alba and a maximum of 0.385 for P. uncinata. The mean value for the softwood species studied was 0.265. Since the Spanish National Forest Inventory (NFI) records species, tree diameter and height of sample trees, these biomass models and ratios can be used to accurately estimate carbon stocks from NFI data.
Highlights
Southern European forests are characterised by a distinctive set of features
We developed root:shoot ratios in order to determine the partitioning into aboveground and belowground biomass
Data for Abies alba were collected in the Pyrenean Mountain Range; for A. pinsapo in the Sierra de Grazalema and Sierra de las Nieves (Southern Spain); for Juniperus thurifera in Guadalajara (Central Spain); Pinus canariensis on the island of Tenerife (Canary Islands); P. halepensis was sampled in the Segura Mountain Range (South East Spain); P. nigra in the Iberian Mountain Range; P. pinaster in the Central Mountain Range (Guadalajara, Central Spain) and the Sierra Morena Mountain Range (Ciudad Real, Southern Spain); P. pinea in the Northern Plateau (Central Spain) and Huelva (South-West Spain); P. sylvestris in the Central Range (Madrid and Segovia, Central Spain) and P. uncinata in the Pyrenean Mountain Range (Fig. 1)
Summary
They support high levels of biological diversity (both plant and animal) as a result of the survival of many species in southern European refuges during the glacial periods They have a harsh, unpredictable climate, difficult socioeconomic conditions and have suffered a long history of over-exploitation accompanied by landscape transformations since ancient times. In the context of this function as mitigators of the effects of climate change, it is important to estimate the quantity of biomass present in forests, to understand the way in which the biomass accumulates and how it is distributed among the different fractions of the tree This information will provide a basis for further nutrient studies and facilitate research on the use of biomass in energy production (Schlamadinger and Marland, 1996; Clark et al, 2001). National Forest Inventories have provided the basis for several regional and national-level carbon budgets (Dixon et al, 1994; Goodale et al, 2002)
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