Modeling inputs of large woody debris to streams from falling trees

A probabilistic model predicts means and variances of the total number and volume of large woody debris piecesfalling into a stream reach per unit time. The estimates of debris input are based on the density (trees/area), tree sizedistribution, and tree-fall probability of the riparian stand adjacent to the reach. Distributions of volume, length, andorientation of delivered debris pieces are also predicted. The model is applied to an old-growth coniferous stand inOregon's Cascade Mountains. Observed debris inputs from the riparian stand exceeded the inputs predicted from treemortality rates typical of similar nonriparian stands. Debris pieces observed in the stream were generally shorter, withless volume per piece, than those predicted by the model, probably because of bole breakage during tree fall. As asecond application, predicted debris inputs from riparian management zones of various widths are compared with theinput expected from an unharvested stand.