Alternativas de manejo silvícola para la conservación de nutrientes en sistemas forestales en Misiones, Argentina

The aim of this study was to evaluate the effects of thinning intensity and type of harvest on the conservation and stability of nitrogen (N), potassium (K), calcium (Ca) and manganese (Mg) in the different strata of a 20 year-old Pinus taeda L. plantation. The study was conducted in Misiones, Argentina (25o59’ S - 54o24’ O). The forestation was planted in 1985 and was thinned to three intensities (0, 33 y 66% of the Basic Area of the non-thinned plantation), under a randomized complete block design. In 2005, the remaining trees of the three thinning intensities were harvested [711 pl ha-1 (0%), 364 pl ha -1 (33%) and 122 pl ha -1 (66%)] and the harvest types were simulated (hole stem, HS, and hole tree, HT). The nutrient content in each of the treatments was determined in tree, bushes, herbaceous vegetation, forest floor and soil. The N, K, Ca and Mg contents decreased when the thinning intensity increased (0.33 y 66%). The same order was observed for the nutrient exports for HS and HT, with significant differences between harvest type (P<0.05). Nutrients remaining in the ecosystem did not differ between thinning treatments, but were significantly different between HS and HT. A positive correlation was found between the sum of nutrient contents in the soil and the sum of the nutrient contents in the aerial biomass. The Remnant Nutrient Index (RNI) showed the convenience to apply the HS tree harvest system and to conserve the harvest residues.