Decomposition and nutrient dynamics of oak Quercus spp . logs after five years of decomposition

Decomposition of oak Quercus spp. logs (25-35 cm diameter, 3 m long) was compared among log substrates in Oregon, Minnesota, Kansas and North Carolina during the first five years on the ground. Decomposition of whole logs (weighted by substrate) averaged 0.069 yr~' (±0.16 SD), but followed a 2-exponential model (k = 0.12 yr" year 1 and k = 0.06 yr" years 2-5), reflecting qualitative differences among log substrates (outer and inner bark, sapwood and heartwood). Rapid loss from bark substrates contributed to the initial rapid decay rate. Sapwood decay rate averaged 0.15 yr" and dominated the second log decay rate. Heartwood lost only 6% mass during the first five years, for an overall decay rate of 0.012 yr~' that likely will represent a longer-term third exponential decay rate. Carbon loss amounted to ca 5 kg yr~' per 170 kg log. Nutrient concentrations generally declined during the first five years, but nitrogen, sulfur, and sodium accumulated in sapwood and heartwood during this period. Sulfur content increased in all substrates and doubled in whole logs during this 5-yr period. Complex patterns of nutrient content suggest patterns of microbial colonization and nutrient utilization. Polynomial models were developed to describe rates of carbon and nutrient flux in log substrates.