Bioenergetics and strategies of some Trichoptera in processing and utilizing allochthonous materials

The rate and manner of biomass loss from decomposing Douglas-firand western hemlock boles in mid-elevation forests of the centralCascade Range were measured. Bole bark and wood were consideredseparately. Loss of bole wood due to respiration was measured bychange in bole wood density. Loss of bole wood due to fragmentationwas measured by change in bole volume. Bole species, position (uprightor prostrate), and diameter affected the rate of bole decompositionwith regard to both fragmentation and respiration. Douglas-fir bolesdecomposed slower than western hemlock boles. For both species,upright boles decomposed faster than prostrate boles (k= 0.031 yr-1versus 0.012 for Douglas-fir wood and k= 0.090 yr-1 versus 0.021 forwestern hemlock wood). Fragmentation proceeded at a faster rate thanrespiration for both prostrate and upright Douglas-fir boles.
Decomposing prostrate boles of western hemlock did not fragment.Upright western hemlock boles had substantial fragmentation losses.Seven to thirteen percent of the wood of an upright western hemlockbole was lost each year to fragmentation. The relationship betweenbole size and decomposition rate was complex. For upright boles,decomposition rates increased as bole diameter decreased. Prostrateboles showed no relationship between bole diameter and decompositionrate. Bark loss rates of prostrate boles were similar for both species(k= 0.02 yr-1). Upright boles lost their bark faster than prostrateboles (k= 0.038 yr-1 to 0.14). Bark was lost faster from small thanlarge boles. The decomposition data for all boles were quite variable.
A computer simulation model was built to attempt to examine thequestion of how the quantity and type of wood and bark of dead boleswould vary in a Douglas-fir/western hemlock forest as the standdeveloped. No age trends were apparent from the model output. Theamount and type of dead bole wood fluctuated within a given range whichwas determined by the stochastic fluctuations in annual mortality.