Heterogeneity of decomposition and nutrient dynamics of oak (Quercus) logs during the first 2 years of decomposition

Abstract

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 2 years on the ground. Decomposition rates (k) for integrated logs averaged 0.28 ± 0.04 year−1 (mean ± 1 SD)) during this initial period. Decomposition reflected qualitative differences among log substrates (outer and inner bark, sapwood and heartwood). Inner bark had the highest nutritional quality and was the focus of insect and microbial activity during this early stage of decomposition; only 20% of initial mass remained after 2 years (k = 0.59 ± 0.15 year−1). Sapwood decayed more slowly than heartwood, with an overall decay rate of 0.20 ± 0.15 year−1). Heartwood lost 50% of its mass during the 1st year, but showed no further loss during the 2nd year, for an overall decay rate of 0.31 ± 0.05 year−1. Nutrient content generally declined during decomposition, but P accumulated in heartwood and Na accumulated in sapwood and heartwood during the 2nd year. Results indicate that decomposition of whole logs integrates different decomposition rates and lag times (i.e., time prior to initiation of decomposition) among log substrates varying in qualitative factors. Multiple-exponential models may be necessary to predict rates and sources of carbon and nutrient release to the atmosphere and soil.