Nitrogen and phosphorus stores in Peatlands drained for forestry in Finland

Nitrogen and phosphorus concentrations were determined for surface peat samples for 78 sites on both undrained and drained pine mires. The oldest areas had been drained 55 years earlier. Generally, the N and P stores in a 0–50 cm peat layer increased with increasing drainage age in oligo‐ombrotrophic sites, and remained unchanged in meso‐oligotrophic sites, even if large quantities were bound up in the increasing tree stand biomasses. This was mainly caused by post‐drainage subsidence of the mire surface and the consequent compaction, which increased the peat bulk densities and brought new stores from deeper peat layers into the layer under observation. Measured stand volumes and published values for N and P concentrations of tree stand compartments were used to estimate the amounts of N and P bound up in the tree stands. The estimates of N and P in the tree stands of the oldest drainage areas were considerable (ca. 400 kg N and 40 kg P ha‐1 in the meso‐oligotrophic and ca. 300 kg N and 30 kg P ha‐1 in the oligo‐ombrotrophic sites), but were small when compared to the stores in the peat (ca. 10 000 kg N and 400 kg P ha‐1 in the meso‐oligotrophic and ca. 7000 kg N and 300 kg P ha‐1 in the oligo‐ombrotrophic sites in the 0–50 cm layer).