Decomposition of Nothofagus fallen woody debris in forests of Tierra del Fuego, Argentina

Abstract

We report the decay constants of fallen fine (<1 cm in diameter) and coarse ($1 cm) woody debris of the southern beeches lenga (Nothofagus pumilio(Poepp. et Endl.) Krasser), nire (Nothofagus antarctica(Forst.) Oerst.), and guindo (Nothofagus betuloides(Mirb.) Oerst.) in Tierra del Fuego, Argentina. The decomposition of small branches (<1 cm) was assessed with the nylon mesh bag technique. A tethered-branch method was used for the decomposition of branches 1-16 cm in diameter of nire and guindo incubated in the field for a period of approximately 4 years. For large lenga branches (8-17 cm) and boles (19-60 cm), we used a chronosequence method, using a 3.5- to 55-year series of natural field incubations. Small lenga branches decayed faster (k =0 .47 ·year -1 ) than those of nire (k =0 .23 ·year -1 ) and guindo (k =0 .17 ·year -1 ). For branches 1 cm, decomposition rates of the species were not significantly different, but diminished with diameter increase. The rate of change of k versus diameter was significantly greater for lenga. In the full range of lenga wood diameters studied, k decreased exponentially with diameter (k =0 .553 ·exp(-0.177·diameter)) attaining a nearly constant value (k =0 .010 ·year -1 ) between 30 and 60 cm. Residence time increased from 2 to 100 years for small branches to large boles, respectively. There was no lag time for decomposition initiation. The decay constants for large lenga branches and boles appeared similar to or slightly greater than those of cold temperate conifers and less than those of hardwoods of the cold and warm temperate zones of the Northern Hemisphere. Resume : Cet article traite des constantes de decomposition des debris ligneux tombes au sol, fins (<1 cm de diametre) et grossiers ($1 cm), des lenga (Nothofagus pumilio(Poepp. et Endl.) Krasser), nire (Nothofagus antarctica(Forst.) Oerst.) et guindo (Nothofagus betuloides(Mirb.) Oerst.) a la Terre de Feu, en Argentine. La decomposition des petites branches