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The present study aims to quantify the carbon stored in a degraded cork oak (Quercus suber L.) ecosystem in the north west of Morocco, in view of potential management implications. To this end, carbon stocks were evaluated in the first 100 cm of the soil, the cork oak trees, and the understorey species (both above-and belowground). Results show that the total carbon stocks in the cork oak ecosystem ranges from 65 to 237 Mg ha -1 with a mean value of 121 Mg ha -1 . The first 100 cm of the soil (including the forest floor) represents the largest carbon pool (~51% of the total organic carbon) of the ecosystem. Tree biomass (above-and belowground tissues of cork oak) represents the second largest pool (47%), whereas the contribution of the understorey is less than 2%. Within the first 100 cm of the soil, over 87% of all the soil organic carbon is situated in the first 40 cm of the soil depth. The amount of carbon stored here ranges from 30 to 110 Mg ha -1 and these organic carbon stocks vary considerably with the stand basal area of the cork oak (R 2 = 0.82). In practice, the carbon stocks of the different pools considered are strongly correlated with the stand density of the cork oak stands. In the semi-arid forest ecosystems of our study, management prescriptions aiming at increasing the standing biomass of the cork oak should thus considerably contribute, both directly through tree biomass and indirectly through increased soil organic matter, to efficient carbon sequestration.

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& Key message Short-rotation forestry using eucalyptus in degraded oak forests in the semi-arid area of NW Morocco can be a useful strategy to avoid further degradation and carbon loss from this ecosystem, but it might be constrained by nutrient and water supply in the long term. & Context Land degradation and deforestation of natural forests are serious issues worldwide, potentially leading to altered land use and carbon storage capacity. & Aims Our objectives were to investigate if short-rotation plantations can restore carbon pools of degraded soils, without altering soil fertility. & Methods Carbon and nutrient pools in above-and belowground biomass and soils were assessed using stand inventories, harvested biomass values, allometric relationships and selective sampling for chemical analyses. & Results Carbon pools in the total ecosystem were low in the degraded land and in croplands (6-13 Mg ha −1) and high in forests(66-94ineucalyptusplantations;86-126innativeforests).Thesoilnutrientstatusofeucalyptusstandswasintermediate between degraded land and native forests and increased over time after eucalyptus introduction. All harvest scenarios for eucalyptus are likely to impoverish the soil but, for the moment, the soil nutrient status has not been affected. & Conclusion Afforestation of degraded land with eucalyptus can be a useful restoration tool relative to carbon storage and soil fertility, provided that non-intensive forestry is applied.

Résumé.-La présente étude a été réalisée dans la chênaie verte du Moyen Atlas central marocain (Tafachna et Reggada), avec pour objectif la détermina-tion du stock de carbone organique dans les différentes couches des sols, de la litière et des différentes composantes de l'arbre (bois du tronc, écorce, branches, rameaux et feuilles). Il en ressort que le stock de carbone total (SCOT) dans cet écosystème est de 145 t C/ha pour Tafachna et 114 t C/ha pour Reggada. Le stock de carbone organique des sols (SCOS) représente plus de 50% du SCOT. Le SCOS varie considérablement avec la densité du peuplement, avec 80 t C/ha pour Tafachna (5192 pieds/ha) et 56 t C/ha pour Reggada (1584 pieds/ha). Au contraire, le stock de carbone dans la biomasse arborée (aérienne et racinaire) est plus important dans Tafachna que dans Reggada (64 t C/ha pour Tafachna et 58 t C/ha pour Reggada). Plus de 80% du stock de carbone organique des sols sont emmagasinés dans les trente premiers centimètres, où il est de l'ordre de 63 t/ha (43% du SCOT) pour Tafachna et 47 t/ha (41% du SCOT) pour Reggada.Mots clés : minéralisation -carbone organique -biomasse -sol -litière.Abstract.-The present study was carried out in Quercus ilex forest of the Middle Moroccan Central Atlas (Tafachna and Reggada). It aims at the determination of the organic carbon stock in the various layers of the soils, the litter and the various components of the tree (wood of the trunk, bark, branches, smal branches and leaves). It comes out from this study that the stock of total carbon (SCOT) in the ecosystem of the holm oak is of 145 t C/ha for Tafachna and 114 t C/ha for Reggada. The organic carbon stock of soils (SCOS) represents more than 50% of the SCT. This stock varies considerably with the density of peuplement with 80 t C/ha for Tafachna (5192 species/ha) and 56 t C/ha for Reggada (1584 species/ha). Contrary to the carbon stock in the phytomass which is equal 64 t C/ha for Tafachna and 58 t C/ha for Reggada. More than 80% of the organic carbon stock of the soils is stored in the first 30 centimeters, that is about 63 t/ha (43% of the SCOT) for Tafachna and 47 t/ha (41% of the SCOT) for Reggada.