Residence time and decomposition rate of Pinus pinaster needles in a forest floor from direct field measurements under a Mediterranean climate

Pinus pinaster (Soland) litter was sampled from a Mediterranean forest floor in order to study decomposition kinetics under natural conditions. Needles were divided into five distinct and successive compartments L, F1a, F1b, F2a, F2b, according to their morphology. The methods of Kendrick (Kendrick, W.B., 1959. The time factor in the decomposition of Coniferous leaf litter. Canadian Journal of Botany 37, 907–912) and Gourbière, (Gourbière, F., 1981. Vie, sénescence et décomposition des aiguilles de sapin (Abies alba Mill.) Part I: Méthodologie et premiers résultats. Acta oecologica, Oecologica Plantarum 2, 223–232) were used to determine the mass loss of each compartment. On the forest floor, the total needle compartment represented 39% of the total decomposing litter mass and the five distinct compartments had similar mass values of 2.8–3.1 t ha−1 ash-free material. The decomposition rate of each compartment was calculated from the mass compartment, its mass loss and the litter-fall in the site. The remaining mass in relation to calculated time was described by a single first-order decay model with a decomposition rate (k) of 0.135 year−1 (R2=0.86) or by an asymptotic model with k=0.180 year−1 and the asymptote at 83.2% R2=0.87. The first-year mass loss equalled 13%, and after 5.1 years it reached 50% for both models.