Biomass decomposition and upper soil nutrient dynamics as affected by different techniques of treating pruning and thinning residues of ponderosa pine afforestations located in an environmental gradient of Patagonia, Argentina

NATALIA SOLEDAD LEDERER; MARÍA MELISA RAGO; MARÍA MARCELA GODOY; GUILLERMO EMILIO DEFOSSÉ

Orlando

Congreso; 7th International Fire Ecology and Management Congress; 2017

The Association for Fire Ecology

Ponderosa pine stands are planted in the central-eastern slope region of Patagonian Andes in Argentina. This region presents a huge environmental gradient, comprising xeric areas at low altitudes (400 to 600m.a.s.l.), in which precipitation reaches 300-400 mm yr., to mesic sites at higher altitudes (600 to 1000 m.a.s.l.), in which precipitation rises from 600 to 1200mm yr. Most of the ponderosa pine stands located in these areas are reaching ages in which different silvicultural practices (mainly thinning and pruning) are needed to obtain healthy and good quality timber, avoiding at the same time fuel continuity for reducing fire risk. However, thinning and pruning produce residues that are generally left on site, generating difficulties for understory plant growth and increasing fire risk. This study has the objectives of determining, in three sites representative of the environmental gradient, the effects that three techniques of residues treatment, namely: 1) prescribed burning; 2) mastication; 3) mastication +prescribed burning; and 4) control or no treatment) had on biomass decomposition and some soil properties. After two season after treatment setting, decomposition rate was rater similar on almost all treatments and sites. Only site three presented higher decomposition rates than the others, probably due to a slightly deeper installation of decomposition bags in the upper organic soil horizon. Soil pH tend to increase from soil surface to deeper soil horizons in most treatments and sites. Only in the xeric site, the burned treatments (prescribed burning and mastication plus prescribed burning) showed significant differences in pH in the first 10 cm of soil depth. Available phosphorous and sulfur showed no discernible trends considering sites and treatments. These preliminary results showed that independent of their cost, the three treatments could be used for residues reduction without causing significant changes in upper soil properties.