Woody Debris as a Source of Fine Particulate Organic Matter in Coniferous Forest Stream Ecosystems

Abstract

The potential contribution of woody debris to fine particulate organic matter pools (0.45 μm ≤ FROM < 1 mm) was investigated in a coniferous forest stream ecosystem in western Oregon. The amount of wetted surface area of both large (>10 cm) and fine woody debris (1–10 cm) was 0.018 and 0.069 m2∙m−2 stream bed, respectively, during summer base flow. These values increase to 0.062 and 0.195 m2∙m−2 stream bed during winter flows. Studies of vertical distribution indicated that most fine wood is concentrated within 0.3 m of the stream bottom, while large wood is more evenly distributed up to 0.7 m. Lignin concentrations of large wood, soil, and FROM were very similar. Examination of FPOM samples with scanning electron microscopy revealed an abundance of wood-derived particles. Erosion rates of wood surfaces ranged between 0.5 and 11 mm∙yr−1 depending on decay state of the log. Using conservative estimates of processing rates, woody debris could be a source for approximately 90 g∙m−2∙yr−1 of FPOM, but with slightly a less conservative estimate, wood processing could easily generate several times the FPOM that is contributed by leaf and needle litter.