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Fate of a Wet Montane Forest During Soil Ageing in Hawaii
Kanehiro Kitayama, Edward A. G. Schuur, Donald R. Drake and Dieter Mueller-Dombois
Journal of Ecology
Vol. 85, No. 5 (Oct., 1997), pp. 669-679
Published by: British Ecological Society
Stable URL: http://www.jstor.org/stable/2960537
Page Count: 11
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1 We chose seven sites across the Hawaiian archipelago differing only in substrate age (400 years to 4.1 × 106 years). All sites were at 1200 m elevation, and mean annual rainfall was ⩾ 4000 mm. This chronosequence reflects long-term ecosystem development from basaltic lava parent material under a humid climatic regime. 2 Live above-ground biomass of woody species ⩾ 1 m tall changed unimodally along the chronosequence from 217 tons ha-1 at the youngest site to a peak of 406 tons ha-1 at the 5000-year site, before declining to 75 tons ha-1 at the oldest site. 3 The size of the soil organic C pool above sub-surface lava or hardpan initially followed the pattern of above-ground biomass, increasing from the youngest site to the 5000-year site, and declining at the 9000-year site. However, it then steadily increased to the oldest site. The proportion of above-ground biomass C to the total C (above-ground biomass + soil) decreased linearly against logarithmic age from 74% at the youngest site to 8% at the oldest site. 4 Net soil N mineralization rate increased from the youngest site to the 5000-year site, and then declined with age to a nearly constant value except for an outstandingly high value at the oldest site. Exchangeable Ca and available P in topsoil increased from the youngest to the 5000-year site, before declining at older sites. 5 Soil redox potential (Eh7) was invariably high (⩾ c. 500 mv) at the sites ⩽ 9000 years, but declined at two old sites (410 000 years and 4100 000 years). 6 Live fine-root biomass in the topsoil increased steadily with substrate age. The distribution of fine roots in the soil profile was positively correlated with redox values. 7 High precipitation rates appear to lead to the development of iron hardpan during pedogenesis. This in turn initiates a positive feedback that promotes waterlogging and anaerobiosis, resulting in reduced organic matter mineralization and increased soil C accumulation. Reduction of biomass with age can be explained by increasingly restricted root penetration, as well as by the reduction in available soil P, N and Ca as a result of geochemical immobilization, leaching and/or reduced mineralization.
Journal of Ecology © 1997 British Ecological Society