Estimation of carbon stocks in a beech forest (Fougères Forest – W. France): extrapolation from the plots to the whole forest

Abstract

-The Kyoto Conference identified the need to establish an accurate inventory of carbon stocks in forests. Carbon stocks were estimated in a beech forest (Fougères forest -France) using a combination of in situ field samples with existing soil and vegetation maps. Soil, humus and vegetation stocks were measured at 100 sampling points distributed throughout representative classes within the entire forest massif. Carbon levels in the soil and humus were determined in the laboratory; models predicting the biomass were used to estimate the stocks in the vegetation. From the statistical analyses and existing maps these point data were extrapolated to the whole forest using two changes of scale. The total carbon stock was estimated to lie in a range between 442 200 and 505 105 tC (a difference of 15%). Half of the carbon stock was found in the soil, 45% in the vegetation and 5% in the humus. To evaluate the accuracy of this estimate, possible sources of error were examined and quantified. The carbon stocks in the vegetation were the most variable. Nevertheless, the results are likely to be integrated into future forest management plans and generalised in other contexts to evaluate carbon stocks at a regional scale.carbon stocks / forests / Fagus sylvatica / scale change / soil / humus / vegetation Résumé -Estimation du stock de carbone dans une hêtraie (forêt de Fougères, Ouest de la France) : extrapolation de la parcelle au massif. La conférence de Kyoto a révélé le besoin d'établir un inventaire précis des stocks de carbone en milieux forestiers. Les stocks de carbone ont été estimés dans une hêtraie (forêt de Fougères, France) en combinant un échantillonnage sur le terrain avec des cartes existantes du sol et de la végétation. Les stocks de carbone dans le sol, les humus et la végétation ont été mesurés sur 100 points distribués dans les classes représentatives de l'ensemble du massif forestier. Les teneurs en carbone dans le sol et les humus ont été déterminées par analyses au laboratoire. Pour la végétation, des modèles de biomasse carbonée établis dans divers peuplements du massif ont ensuite été utilisés pour les autres peuplements. Après analyse statistique de la variabilité, et sur la base des cartes disponibles, les valeurs des stocks de carbone ont été extrapolées à l'ensemble du massif forestier en utilisant deux changements d'échelle. Le stock total de carbone a été estimé dans une fourchette entre 442 200 et 505 105 tC (un écart de 15 %). La moitié du stock de carbone se trouve dans le sol, 45 % dans la végétation et 5 % dans les humus. Pour évaluer la qualité de ces estimations, les sources d'erreurs ont été examinées et quantifiées. La variabilité est la plus élevée dans le compartiment de la végétation. Cette démarche devrait être généralisée à d'autre conditions écologiques afin d'améliorer l'estimation des stocks de carbone de la forêt française.

Variabilité spatiale des réserves de nutriments dans les humus et les sols d’un massif forestier (Fougères, France)

“…A non-carbonated Aeolian loam covers the main area of the forest. The loam is about 1.5 m thick in the south and east of the forest, and less in the west; it contains about 15% clay and 75% silt [28]. Toutain [44] pointed out the homogeneity of these forest soils, which are mainly classified as Alocrisols-Neoluvisols [1].…”

“…The number and sometimes the complexity of the variation factors previously cited probably explain the small number of spatial distribution studies on soil chemical properties under forest [10,20,28,39,48]. Further developments in this domain are also required and could improve the future management of forests (for example, well thought-out enrichment in damaged forest ecosystem or the choice of appropriate forest species) in a context of ecosystem sustainability [31].…”

“…Several approaches, summarised by Ryan et al [39], make the study or the cartography of nutrient stocks possible: the use of environmental correlation models [39], geostatistical methods [20] or stratification methods [10,28,48] which offer advantages. In fact, stratification, following detailed identification of variation factors, allows one to investigate the distribution of element stocks at different spatial scales at an acceptable cost, such as the carbon in Lecointe et al [28].…”

“…The objectives were (i) to determine which factors among those studied (age of stand, type of stand and type of soil), influence the nutrient stocks in soils and humus, and (ii) to verify whether a stratification method previously used to investigate carbon stocks could be used for nutrient stocks. For that, we reused a stratification method initially developed by Lecointe et al [28] for the estimation of carbon stocks at the same site. Measurements at sampling points distributed throughout the forest massif, allowed us to estimate the nutrient stocks at specific points.…”

“…Regarding short range variability, several studies point out that individual trees can affect the chemical properties of soil (such as pH, organic carbon, Ca, Mg, P and N concentrations) in their proximity, at ranges of 25 m or less [8,11,19,20,38]. Regarding wide range variability (ranges superior to 50 m), studies have proved that soil chemical properties vary with soil type, present pedogenesis, nature of parental material [45], soil position in the landscape [43], tree species [4,5], stand age [18,28,29,47] and type of forest management [32]. The major difficulty is that wide range variability may be concealed by short range variability.…”