Stand dynamics of Dacrydium cupressinum dominated forest on glacial terraces, south Westland, New Zealand

Stand structure, disturbance histories, and patterns of tree replacement of three conifer-dominated stands growing on glacial terraces, differing in age, were investigated. Regeneration patterns of the conifers Dacrydium cupressinum, Manoao colensoi, Prumnopitys ferruginea and Phyllocladus alpinus were inferred from age and size (diameter) distributions, the spatial distribution of tree ages, and tree locations. Disturbance histories and patterns of tree replacement were reconstructed from age distributions, the spatial distribution of tree ages, and tree locations. Disturbance histories were related to soil drainage which was inferred from the depth of rusting on mild steel rods inserted across each stand. Stands differed in structure and composition, reflecting different patterns of disturbance. Manoao colensoi and Dacrydium cupressinum were established in response to catastrophic disturbance on extremely poorly drained soils on the oldest terrace. On less poorly drained soils, Dacrydium cupressinum, Prumnopitys ferruginea and Phyllocladus alpinus were established in response to smaller canopy gap formation from intermittent windthrow and synchronous canopy collapse. A secular model of stand dynamics is envisaged across the glacial terraces, reflecting an even long-term soil development, where the chance of catastrophic disturbance will increase as soils become increasingly poorly drained over millennia. The implications of these findings for sustainable forest management are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.