Resumen

GOYA, Juan F; PEREZ, Carolina; FRANGI, Jorge L  y  FERNANDEZ, Roberto. Harvesting effects and residue fate on nutrient stability of Pinus taeda L. plantations. Ecol. austral [online]. 2003, vol.13, n.2, pp.139-150. ISSN 1667-782X.

This paper reports on the aboveground nutrient content at rotation time in Pinus taeda plantations of northern Misiones province, and assess the impact of three simulated harvest strategies on nutrient stability (exported nutrients/nutrients in soil): (1) harvest of marketable products (stems with bark up to 5 cm diameter) and slash abandonment on the site, (2) harvest and withdrawal of all the standing aboveground biomass (whole tree utilization), and (3) harvest of marketable products and slash burning in situ. The aboveground biomass plus litter mineral content per hectare was: 194 Mg for C, 1018 kg for N, 480 kg for Ca, 335 kg for K, 97 kg for Mg and 42 kg for P. Of these, 95% (C), 83% (N), 88% (Ca), 94% (K), 91% (Mg), and 79% (P) were in the aboveground biomass. P and K showed the most unbalanced budget (highest stability index) under the three scenarios. The least conservative harvest type (harvest of marketable products and slash burning) negatively impacted on nutrient stability by a factor of 1.4 (K, Ca and Mg), 1.8 (N), and 2.3 (P) times more than the most conservative one (stem harvest only). Assuming that the rate of spontaneous net reposition of nutrients to the soil within the time frame of a given rotation cycle is non-significant, and that fertilisers are not added, the most extractive harvest practice will reduce the exchangeable nutrient stock in the short-term, attaining critical thresholds of the nutritive stability index for P and K in about two rotations. With actual management practices, these observations put uncertainties in the sustainability of the currently high rates of production of these forest crops.

Palabras clave : Subtropical plantations; Conifers; Nutrient stability index; Misiones; Harvest nutrient budget.

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