Cation storage and availability along a Nothofagus forest development sequence in New Zealand

Soil cations and pH were determined in relation to the development of even-aged (10, 25, 120, and >150-year-old stands) mountain beech (Nothofagus solandri var. cliffortioides (Hook.f.) Poole) forest after catastrophic canopy disturbance. Live stem biomass varied from 1 to 273 Mg/ha between the seedling (10 years) and pole (120 years) stages, respectively, but was less in the mature stage (>150 years; 245 Mg/ha). Coarse woody debris mass declined monotonically from 168.7 Mg/ha in the seedling stage to 23.7 Mg/ha in the mature stage. Total cation (Ca, Mg, and K) storage in wood (live stem biomass plus coarse woody debris) was highest in the pole stage and least in the sapling stage (25 years) because sapling stands had low stem biomass and only intermediate levels of woody debris. This matched high soil cation availability in the sapling stage and low availability in the pole stage. Between these stages soil pH declined and inorganic monomeric aluminium increased. The seedling and mature stages often had intermediate levels of soil-available cations and pH. This study does not support the hypothesis that sequestering of cations in aggrading biomass necessarily results in a monotonic decline in soil cation availability as forests develop; instead mountain beech exhibits a bimodal pattern for soil cations. The reciprocal oscillation of nutrients between living wood, deadwood, and the soil contributes in a major way to these patterns.