Effects of alternative silvicultural systems on litter decomposition and nutrients dynamics in sub-Antarctic forests

Abstract

Forest harvesting is one of the main economic practices in South Patagonia. The impacts produced by forest harvesting have been studied by numerous investigations. And it is known that forest harvesting affects the decomposition of soil organic matter. However, there is no data about how the harvesting by variable-retentions affect this decomposition. Our objective was to determine how impact variable-retention upon decomposition and nutrient release in Nothofagus pumilio forest soils. We hypothesized that variable-retention accelerate decomposition and nutrient release. We compared primary and harvested forests with two types of retentions (aggregated and dispersed) and two times [1 and 5 years after harvesting (YAH)]. To measure litter decomposition, we used bag technique for to determine organic matter loss. We determined carbon; nitrogen; calcium; potassium; magnesium and lignin concentrations in decomposing material. We analysed the data using linear mixed models ANOVA. Decomposition rates were estimated as derivate of the linear mixed model for the logarithm of the remaining leaf litter weight. We found that dispersed retentions treatment had the highest decomposition rates. Primary forest and aggregated retentions had the smaller slopes of the decomposition model. Dispersed and aggregated retention 5 YAH retained more nitrogen compared to primary forest. Dispersed retention 5 YAH had the lowest C/N ratio. Primary forest had higher Lignin/N ratio at 540 incubation days. Dispersed retention 5 YAH released more phosphorus compared to primary forest. Dispersed and aggregated retention 1 YAH had higher C/P ratio. Dispersed retention 5 YAH presented the most mineralization of potassium in the initial time of decomposition. We conclude that the harvesting by variable-retentions had an immediate negative effect on litter decomposition and the nutrients dynamics.