Evaluación de la producción de mantillo en plantaciones comerciales de Eucalyptus dunnii y Eucalyptus grandis

Litterfall represents an important pathway for the return of carbon (C) and nutrients to the soil in forest plantations, and its dynamics may vary according to species, stand age, and climatic conditions. In Uruguay, this flux and its contributions of C and nitrogen (N) have been scarcely studied. The objective of this study was to quantify litterfall production in commercial Eucalyptus grandis and Eucalyptus dunnii plantations managed for pulp production, evaluating differences between species, the contribution of the main litter fractions, as well as C and N inputs and their associations with climatic variables. The study was conducted in 2-, 7-, and 12-year-old stands located in Río Negro, Uruguay. Nine conical litter traps were installed in each stand, and the collected material was separated into leaves, branches, and other structures, and its dry biomass was determined. Carbon and N concentrations were determined in composite samples using an elemental analyzer. Seasonal litterfall production was analyzed using linear mixed-effects models, while associations with climatic variables were assessed through correlation analyses. Litterfall production showed marked seasonality, with higher values in spring and summer and lower values in autumn and winter. At the annual scale, no significant differences between species were detected in the 2-year-old stands, with production values of 4.60 and 4.16 Mg ha^-1 yr^-1 for E. grandis and E. dunnii, respectively. In contrast, in the 7- and 12-year-old stands, E. grandis showed significantly higher litterfall production, reaching 7.82 and 7.03 Mg ha^-1 yr^-1, compared with 4.58 and 3.75 Mg ha^-1 yr^-1 in E. dunnii, respectively. Leaves constituted the main litterfall fraction, although the contribution of branches and other structures was greater in the 7- and 12-year-old stands. Carbon patterns closely followed those of biomass, whereas N showed a different response: in 2-year-old stands, E. dunnii had a greater annual N input than E. grandis, whereas in the 7- and 12-year-old stands, E. grandis showed greater N inputs. Seasonal litterfall production was positively associated with temperature, radiation, and wind speed, and negatively associated with relative humidity, whereas cumulative precipitation showed weak and variable associations; these relationships were interpreted as exploratory. Overall, the results demonstrate marked seasonality in litterfall production and differences between the evaluated species that varied among stands of different ages, together with changes in litter composition and C and N fluxes.