Document: HUA-3-58-21

Woody root decomposition in coniferous forests of the Pacific Northwest: A time series approach.

CHEN, H.*, M.E.HARMON, J.SEXTON and B.FASTH

Oregon State University, Corvallis, OR 97331 ¹

Abstract:
Woody root decomposition was studied in Sitka spruce, Douglas-fir, and ponderosa pine forests at Cascade Head, H. J. Andrews, and Pringle Falls Experimental Forests in Oregon, using a time series approach. Species significantly influenced mass loss of fine and small roots during the first 2 years of decomposition. In contrast, no significant species effects on the decomposition of medium, large, jumbo roots were observed. For the same period, site differences had little impact on decomposition of roots, regardless of root size. For fine roots, Oregon ash was the fastest among the 15 species examined during two years of decomposition, losing about 63% of its initial mass. Incense-cedar had the slowest decomposition, losing about 35% of initial mass in the same period. Small roots lost 11--35% of initial dry weight among 8 species in 2 years. For other class sizes, 10% or less of the initial mass was lost in 2 years. Initial substrate quality indices could be used to predict the decomposition rate-constant (k) of fine and small roots. For all fine roots, lignin-cellulose index (LCI) and lignin-phenols:N together were the best predictor. In small roots, the phenols:N ratio was the best predictor. Soil nitrogen availability had no direct influences on woody root decomposition despite a 5-fold difference between sites. Decomposing roots, especially fine roots, could be an important nitrogen source with as much as 70 Kg/ha/year of nitrogen released from dead roots after catastrophic disturbances (e.g., clear-cut, forest fire) in Douglas-fir old-growth forests.

Keywords: woody roots, mass loss, N dynamics, lignin: N ratio, the Pacific Northwest.

This abstract is being presented at: 4:30 PM in session:
Oral Session #67: Decomposition Processes.