Water balance of conifer logs in early stages of decomposition

Seasonal and long-term changes in the water balance of conifer logs during the first 8 years of decomposition werestudied in an old-growth Pseudotsugaffsuga forest in the Oregon Cascade Mountains. Measurements were madeof the moisture content of outer bark, inner bark, sapwood, and heartwood and of the flow of water into and outof logs of four species (Abies amabilis, Pseudotsuga menziesii, Thuja plicata, and Tsuga heterophylla). After thelogs had decomposed from 1 to 2 years, 38-47% of the canopy throughfall landing upon them ran off the surface,29-34% leached from the bottom, and 21-30% was absorbed and evaporated. After 8 years of decomposition, waterentering and then leaching from logs increased 1.3 times while runoff decreased a similar amount. The proportionof water stored by and evaporated from logs in this study indicates that in old growth forests they may intercept2-5% of the canopy throughfall to the forest floor and that, even in early stages of decomposition, they may affectthe hydrological cycle of Pacific Northwest old-growth forests.