CATION STORAGE AND AVAILABILITY ALONG A NOTHOFAGUS FOREST DEVELOPMENTSEQUENCE 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 (Noth ofagus solandri var. cliffortioides (Hook.f.) Poole) forest after cata strophic canopy disturbance. Live stem biomass varied from 1 to 273 Mg /ha between the seedling (10 years) and pole (120 years) stages, respe ctively, but was less in the mature stage (>150 years; 245 Mg/ha). Coa rse woody debris mass declined monotonically from 168.7 Mg/ha in the s eedling 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) w as highest in the pole stage and least in the sapling stage (25 years) because sapling stands had low stem biomass and only intermediate lev els of woody debris. This matched high soil cation availability in the sapling stage and low availability in the pole stage. Between these s tages soil pH declined and inorganic monomeric aluminium increased. Th e seedling and mature stages often had intermediate levels of soil-ava ilable 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; ins tead mountain beech exhibits a bimodal pattern for soil cations. The r eciprocal oscillation of nutrients between living wood, deadwood, and the soil contributes in a major way to these patterns.