In the northern hardwood forest, woody debris is an incompletely understood component of nutrient storage and recycling. While most studies of woody debris focus on the fate of large stems, smaller woody debris is also important. During stand initiation following disturbance of northern hardwoods pin cherry often dominates and senesces somewhat synchronously at about age 30, producing a pulse of small woody debris. We hypothesized that the size and nutrient content of fine and coarse woody debris (FWD and CWD) pools varies through forest succession. We measured the volume and biomass of fine (<3.0 cm diameter) and coarse (≥3.0 cm diameter) woody debris on a chronosequence of northern hardwood forest stands ranging from 15 to > 130 years since disturbance. We used line intersect sampling to estimate CWD volume and biomass on 13 stands and fixed area plots for measurement of FWD biomass on 15 stands. CWD was separated by species, FWD was further separated by diameter class, and each were analyzed for their concentrations of nitrogen (N), calcium (Ca), potassium (K), and magnesium (Mg).
Results/Conclusions

Woody debris biomass (CWD + FWD) gradually accumulated in young stands with fluctuating levels tied to stochastic events in aging stands (range of 1-26 Mg/ha). During stem exclusion, the FWD:CWD biomass ratio was 1.3 (± 0.8 SD; n=5), compared to 0.2 (±0.06; n=8) during the rest of stand development. The highest concentrations of Ca (6.8 mg Ca/g wood) and N (6.9 mg N/g wood) were in the smallest-diamter FWD, which also had high K concentrations. Woody debris nutrient pools ranged from 8 - 112 kg/ha Ca, <0.5 - 4 kg/ha Mg, 3 - 65 kg/ha K, and 3 - 48 kg/ha N, which are similar magnitudes to the respective nutrient pools in the Oie layer. Through most of stand development, FWD contained 9 (±4) kg/ha Ca, but this doubled during stem exclusion (18 ±7 kg/ha Ca in FWD), concurrent with a near absence of CWD pools. Declining forest floor cation concentrations have been described for stands aging beyond stem exclusion, which has been attributed to acidic deposition and natural stand aging. Fine woody debris pools may influence forest floor nutrient availability in young stands by providing a sudden pulse of FWD which would decompose relatively quickly.