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.

LEDERER, N. S.; RAGO, M. M.; GODOY, M. M.,; DEFOSSÉ, G. E

Orlando, Florida

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

Association For Fire Ecology

Ponderosapine stands are planted in the central-eastern slope region of Patagonian Andesin Argentina.  This region presents a hugeenvironmental 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 higheraltitudes (600 to 1000 m.a.s.l.), in which precipitation rises from 600 to 1200mm yr.  Most of the ponderosa pine standslocated in these areas are reaching ages in which different silviculturalpractices (mainly thinning and pruning) are needed to obtain healthy and goodquality timber, avoiding at the same time fuel continuity for reducing firerisk.  However, thinning and pruning produceresidues that are generally left on site, generating difficulties for understoryplant growth and increasing fire risk. This study has the objectives of determining, in three sitesrepresentative of the environmental gradient, the effects that three techniquesof residues treatment, namely: 1) prescribed burning; 2) mastication; 3)mastication +prescribed burning; and 4) control or no treatment) had on biomassdecomposition and some soil properties. After two season after treatment setting, decomposition rate was rater similaron almost all treatments and sites.  Onlysite three presented higher decomposition rates than the others, probably dueto a slightly deeper installation of decomposition bags in the upper organicsoil horizon.  Soil pH tend to increasefrom 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 significantdifferences in pH in the first 10 cm of soil depth.  Available phosphorous and sulfur showed nodiscernible trends considering sites and treatments.  These preliminary results showed thatindependent of their cost, the three treatments could be used for residuesreduction without causing significant changes in upper soil properties.