The water vapour conductance of Eucalyptus litter layers

Forest litter layers modify the exchange of water vapour between the soil and atmosphere below the forest canopy. Water vapour fluxes are determined by the conductance of the litter layer, a parameter which has not previously been measured for Eucalyptus litter layers. In this study, the water vapour conductance of Eucalyptus globulus litter layers was examined in the laboratory to provide an observational basis for a model of vertical water vapour transfer in a litter layer. Conductance was measured for four different types of litter layers: 25 and 50-mm thick layers of leaves, a 25-mm layer of compressed leaves, and a 25-mm layer of partially decomposed litter. In addition, the vertical variation of conductance in a 50-mm thick leaf layer was examined. Without wind, the conductance of all four layers was 50-75% less than the measured conductance of a layer of air of the same depth. Conductance increased with increasing wind speed, from 0.5-1 mm s−1 without wind to 7.5-9.5 mm s−1 with a 3.3 m s−1 wind. The ratio of conductance in the top half to conductance in the bottom half of the litter layer increased from 1.3 without wind to 65 with a 3.3 m s−1 wind above the litter layer. This is the first time the dependence of conductance with depth on wind speed has been measured in leaf litter and may have important implications for future model development.