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) wascompared among log substrates in Oregon, Minnesota, Kansas and North Carolinaduring the first five years on the ground. Decomposition of whole logs (weighted bysubstrate) averaged 0.069 yr---1 (±0.16 SD), but followed a 2-exponential model(k = 0.12 yr.' year I and k = 0.06 yr- years 2-5), reflecting qualitative differencesamong log substrates (outer and inner bark, sapwood and heartwood). Rapid lossfrom bark substrates contributed to the initial rapid decay rate. Sapwood decay rateaveraged 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 willrepresent a longer-term third exponential decay rate.
Carbon loss amounted to ca 5 kg yr- per 170 kg log. Nutrient concentrations gen-erally declined during the first five years, but nitrogen, sulfur, and sodium accumulatedin sapwood and heartwood during this period. Sulfur content increased in all sub-strates and doubled in whole logs during this 5-yr period. Complex patterns of nutrientcontent suggest patterns of microbial colonization and nutrient utilization. Polynomialmodels were developed to describe rates of carbon and nutrient flux in log substrates.