Water Dynamics in Conifer Logs in Early Stages of Decay in the Pacific Northwest, USA

Water dynamics in decaying conifer logs of four species (Abies antabilis [Pacific silver fir], Pseudotsuga menziesii [Douglas-fir], Thuja plicata [western red cedar], and Tsuga heterophylla [western hemlock]) were studied in the Coast Range of Oregon. Measurements were made of throughfall, leachate, runoff, and absorption for logs during their 6th through 8th year of decay. During this period 47-70% of the throughfall landing on the logs evaporated, 18-35% flowed through the log and leached out, 3-29% ran off the surface, and absorption accounted for 3-11%. Together absorption and evaporation intercepted 60% of the throughfall impacting the logs. Although the second year of the study had twice as much precipitation as the first, the partition of the fluxes was essentially identical. Direct measurement of the changes in log weight allowed calculation of water stores and the evaporative component; the latter proved to be the largest fraction of the water balance, with the majority of losses during the cool, wet, winter period.