This paper reports spatial and temporal changes at the regional level in soil organic carbon (SOC) using a soil-test database. A total of 23 329 SOC test values recorded between 1990 and 2004 by certified commercial laboratories and collected in a mountainous French region (Franche-Comte´) were integrated in a database. Results show a strong trend in organic carbon content, mainly related to elevation. A large loss in SOC was observed over the survey period. This loss correlated with baseline SOC content with greater loss from soils with higher carbon content. This loss is likely to be due to both changes in land use from permanent grassland to cultivation and to an increase in temperature during the survey period. Our study demonstrates that past soil-test results which were not originally intended for monitoring can provide an alternative method for detecting changes in SOC.

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The practice of applying large amounts of P to agricultural land over several previous decades, particularly in regions with intensive livestock production, has resulted in P accumulation in soils with an increased risk of P losses into water bodies and thus of eutrophication. This work is aimed at analyzing the spatiotemporal changes in extractable soil P content at the regional level by means of a soil test database and then comparing results with independent data from agricultural censuses. A total of 228 079 soil P‐test values [Dyer method: 1:5 soil‐citric acid solution (20 g/L) ratio] generated between 1980 and 2003 by certified commercial laboratories in Brittany (northwestern France) were integrated into a database. Changes in P were analysed by considering four 4–6 year periods between 1980 and 2003 using cumulative frequencies and summary statistics performed on raw soil test values. Then data were aggregated into discrete entities (canton: administrative entities) and summary statistics, linear regression and spatial distribution were carried out. P balances were measured for the same entities taken from the agricultural censuses of 1979, 1988 and 2000. Over the entire study period, a marked spatial variability was observed with higher P content in the western part of Brittany, as well as a systematic increase in median P content with lower amplitude over the past decade. The mean cantonal soil P surplus accumulated over 24 years amounted to 763 kg P/ha of usable agricultural land. Similar P balances sometimes gave rise to widely different increases in P. Cumulative balances were positively correlated with an increase in soil P (r2 = 0.34).

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-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.

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