Distributions qualitative et quantitative des éléments nutritifs dans un jeune peuplement de Pin maritime (Pinus pinaster Ait)

(Reçu le 15 février 1999 ; accepté le 3 mai 1999)Résumé -Afin d'estimer la pérennité de l'alimentation minérale de plantations forestières de Pinus pinaster et Eucalyptus globulus de forte productivité en Galice, nous avons calculé des bilans (entrées-sorties) d'éléments minéraux dans trois petits bassins versants. Dans chacun de ces trois bassins, les sorties par drainage de Ca, Mg et K sont inférieures aux entrées par les pluies. Cette particularité est attribuée à la relative pauvreté en cations alcalino-terreux des roches mères, au très faible drainage de sulfate et nitrate lié à l'absence de pollution atmosphérique, et surtout à la forte immobilisation forestière qui tire directement profit des apports par les pluies. L'exploitation forestière actuelle des peuplements de pins et d'eucalyptus conduit à des bilans fortement négatifs de Ca, Mg et K, mais qui diffèrent peu entre ces peuplements. La différence majeure provient du mode d'exploitation, selon que les arbres sont ou non écorcés en forêt, et que la litière est exportée. La libération par altération minérale d'un flux relativement important de Ca et K est nécessaire pour compenser ces pertes. Les estimations du flux d'altération conduisent à penser que ce flux est suffisant dans le bassin versant sur granodiorite. Dans les bassins versants sur granite, ce flux est vraisemblablement insuffisant en ce qui concerne le Ca, mais des mesures complémentaires sont nécessaires pour pouvoir l'affirmer. Les bilans d'azote montrent qu'une forte fixation symbiotique est indispensable pour assurer la pérennité de la production forestière. bassin versant / Eucalyptus globulus / Pinus pinaster / altération / GaliceAbstract -Budgets of mineral elements in small forested catchments in Galicia (NW Spain). In order to assess the sustainability of mineral supply to fast growing Eucalyptus globulus and Pinus pinaster stands in Galice (NW Spain), we calculated (input-output) nutrient budgets in three small catchments: the Castrove and Jabali catchments with eucalyptus on a base poor granite and the Arcos catchment with pine on granodiorite. In each catchment, the annual drainage output was lower than the rainwater input for Ca, Mg and K. This particularity is attributed to (a) the relative low content of Ca and Mg of the parent material, (b) the very low concentrations of NO 3 and SO 4 of drainage water in an area with very low level of atmospheric pollution, and (c) to the strong mineral uptake of fast growing stands. The present management of forests leads to negative budgets, both in the eucalyptus and pine catchments. But the traditional management of pine stands including the harvest of needles and branches was much more impoverishing than the present management of eucalyptus stands, where timber is the only harvested product. Various estimates of the weathering rate suggest that this flux is sufficient to compensate for the losses in the catchment on granodiorite but probably insufficient on granite. Since nitrogen deposition is extremely low, and forest fires are qui...

Section: Bilans à L'échelle Des Bassins Versantsunclassified

Bilans d'�l�ments min�raux dans de petits bassins versants forestiers de Galice (NW Espagne)

Dambrine¹,

Vega

Rodríguez³

et al. 2000

“…The increased availability of nitrogen accelerated the turnover of this element throughout the system but not its accumulation in perennial organs. Unlike oak species [3,37,41,47,84], beech and other hardwood species do not exhibit differential storage and concentrations of nutrients in the different parts of the tree.…”

Section: Nitrogen Dynamicsmentioning

confidence: 99%

Organic matter and nitrogen dynamics in a mature forest of common beech in the Sierra de la Demanda, Spain

Regina¹,

Tarazona²

2001

-Aboveground biomass, litterfall, leaf weight loss due to decomposition, N return and seasonal leaf N dynamics were studied in the Sierra de la Demanda, Spain, a Mediterranean climatic zone. The forest ecosystem considered was a climax beech (Fagus sylvatica L.) forest. Aboveground biomass was estimated by cutting and weighing seven trees from a beech stand according to diameter classes, recording the categories of trunk, branches and leaves. The results indicate a total biomass of 132.7 Mg ha -1 . The litterfall was 4 682 kg ha -1 yr -1 , although variations from year to year were observed, mostly due to water stress in summer. Greater K (Jenny's constant) and K o (Olson's constant) values were obtained for total litter than for leaves alone. It is possible that the mean soil humidity might not be a limiting factor in the decomposition process and that this effect would be due to the distribution of rainfall rather than to the total amount of precipitation together with elevated temperature and airing of the holorganic soil horizon. The leaf N contents of beeches growing in the Sierra de la Demanda were studied, relating the contents to other structural stand characteristics. For this, N was analysed in shed leaves, in leaf biomass and in leaves decomposing on a test plot in the "Tres Aguas" beech forest. Leaf nitrogen contents were measured over a vegetative cycle in the above beech forest. Finally, leaf nitrogen contents were studied in thirty beech stands in the Sierra de la Demanda located at different altitudes. Annual nitrogen accumulation in leaf biomass was 79.4 kg ha -1 yr -1 , of which 22.9 kg ha -1 yr -1 were returned to the soil substrate through shedding and 2.1 kg ha -1 yr -1 were actually incorporated into the soil. Nitrogen cannot be a limiting factor for the development of the beech stands studied because all of them surpassed the leaf deficiency threshold. Only other factors such as soil texture and structure or silvicultural treatment have a decisive effect on the production of the stand studied. The correlations for leaf nitrogen contents and the structural stand characteristics explored revealed that leaf nitrogen was only slightly correlated with the mean height of the trees at the plot. aboveground biomass / litterfall / weight loss / nitrogen / forest ecosystem Résumé -Dynamique de la matière organique et de l'azote dans une hêtraie de la Sierra de la Demanda (Espagne). La biomasse aérienne, la retombée de litière, la perte de poids de feuilles en décomposition, le retour et la dynamique saisonnière de l'azote des feuilles, ont été estimés dans une hêtraie (Fagus sylvatica L.) de la Sierra de la Demanda, (Espagne). La biomasse a été estimée par coupe et pesée de sept arbres selon la distribution des diamètres. Les poids des troncs, branches et feuilles ont été mesurés. Les résultats indiquent une biomasse totale de 132,27 Mg ha -1 . La chute de litière est de 4 682 kg ha -1 an -1 , cependant on a observé des variations inter-annuelles, principalement dues au stress hydrique esti...

“…BERG-I stand was sampled at 16, 32 and 40 years-old for determination of nutrient concentrations (B16, B32 and B40 samplings; see Lemoine et al, 1988 for more details on B16). BERG-II and BRAY were sampled at 8 and 26 yearsold respectively (B08 and B26).…”

Section: Study Sites and Treesmentioning

confidence: 99%

Improving models of forest nutrient export with equations that predict the nutrient concentration of tree compartments

Augusto¹,

Meredieu

Bert

et al. 2008

, et al.. Improving models of forest nutrient export with equations that predict the nutrient concentration of tree compartments. Annals of Forest Science, Springer Verlag/EDP Sciences, 2008, 65 (8), pp.1. Ann. For. Sci. 65 (2008) Abstract• The objective of this study was to explore the distribution of major nutrients (N, P, K, Ca and Mg) in the aboveground compartments of an intensively managed tree species (Pinus pinaster Ait.). A total of 53 trees were cut down in even-aged stands respectively 8, 16, 26, 32 and 40 years old. The nutrient concentrations of the aboveground compartments were analysed.• Nutrient concentrations of foliage did not vary with any of the variables used, except needle age. Nutrient concentrations of living branches, stem bark, stem sapwood, stem heartwood, stemwood and stem decreased with increasing branch diameter, bark thickness, sapwood thickness and heartwood thickness, respectively. Beyond a certain value of the predictive variable (stem diameter ≈ 15 cm; branch diameter ≈ 2.5 cm), the concentration of all the nutrients stabilised.• A 50 year-old pine stand was used to obtain a validation dataset for nitrogen concentration. For this nutrient, the regression relationships gave satisfactory estimates for most compartments (mean error = 12-25%) and particularly for the stem.• A procedure is proposed to estimate the nutrient exports associated with harvests of Pinus pinaster biomass. • L'objectif de cette étude est d'explorer la distribution des éléments majeurs (N, P, K, Ca, Mg) dans les compartiments aériens d'une essence gérée de manière intensive. Au total, 53 pins maritimes (Pinus pinaster Ait.) ont été abattus parmi des peuplements équiennes de 8, 16, 26, 32 et 40 ans. Mots-clés• Les concentrations en nutriments du feuillage ne varient pas pour une classe d'âge d'aiguilles donnée. Les concentrations des branches vivantes, de l'écorce, de l'aubier et du duramen décroissent lorsque le diamètre ou l'épaisseur du compartiment considéré augmente. La concentration de l'ensemble des nutriments devient constante lorsque la variable prédictive (diamètre ou épaisseur) atteint une valeur plateau.• Un jeu de données de validation pour les concentrations en azote, provenant d'un peuplement équienne de pins de 50 ans, permet de confirmer les performances satisfaisantes des modèles construits (erreur moyenne = 12-25 %) et en particulier pour le tronc.• Une procédure d'estimation des exportations de nutriments associées aux récoltes de biomasse de Pinus pinaster est présentée.