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Carbon, water and nutrient balances of a Eucalyptus grandis plantation in Brazil over 5 years

Nouvellon Y., Stape J.L., Bonnefond J., Le Maire G., Christina M., Campoe O., Hakamada R., Loos R., Bouillet J.P., Laclau J.P.. 2014. International Forestry Review, 16 (5) : p. 258. IUFRO World Congress. Sustaining Forests, Sustaining People: The Role of Research. 24, 2014-10-05/2014-10-11, Salt Lake City (Etats-Unis).

Eucalyptus grandis plantations in Brazil are among the most productive forests of the world, reaching mean annual increments of about 50 m3/ha/yr over short (6 yr) rotations. Carbon, water, and nutrients budgets in one of these plantations were investigated through continuous eddy-covariance measurements of water vapor and CO2 fluxes over a 5-yr period encompassing two successive rotations (2 yr before and 3 yr after harvesting and replanting), with measurements of water table depth, soil water content to a depth of 10 m, and concentrations of nutrients in soil solutions. Before clearcutting, fine roots were found to a depth of 16 m. No seepage occurred below 5 m. Actual evapotranspiration (AET) was approximately equal to annual precipitation (1350 mm). Clearcutting resulted in a strong decrease in AET, a recharge of deep soil layers, and a rise in the water table. By the third year after replanting, the rapid increase in AET supported by the fast expansion of roots led to soil water depletion to a depth of 10 m. Clearcutting turned the forest from a strong C sink (net ecosystem productivity of about 1 tonne C/ha/month) into a C source, but the plantation turned back to a C sink from 7 months after replanting onwards.

Mots-clés : eucalyptus grandis; bilan hydrique; Équilibre nutritif (plante); plantation forestière; Évapotranspiration; analyse de covariance; brésil; covariance des turbulences

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