A SOIL-SITE EVALUATION INDEX OF PRODUCTIVITY IN INTENSIVELY MANAGED PINUS-RADIATA (D-DON) PLANTATIONS IN SOUTH AUSTRALIA

A limiting-factor, environmental model for radiata pine (Pinus radiata (D. Don)) has been developed using landform and soil morphological fe atures that influence site productivity. The model focuses on soil and landscape constraints to productivity and predicts the native product ivity of land and tree species. It permits the integration of land-use objectives for a catchment through forest management and use of silvi cultural practices which increase productivity. The soil site evaluati on index (SSEI) is an index of forest productivity found when silvicul ture extends only to the minimum amount of site disturbance needed to establish a plantation of radiata pine. The impacts of intensive silvi cultural practices were deducted from the 'Site Quality' productivity survey rating to calculate the unimproved yield class (uYC). We calcul ated SSEI by range standardising uYC values from 0 to 1. SSEI was corr elated with the environmental factors in a regression tree model using readily available analytical software. The model accurately predicts unimproved forest productivity from observed soil horizon and land sur face properties. The environmental constraints in low lying areas rela te to waterlogging, soil sodicity and gravel content. In elevated area s, plant available water storage, rock weathering, landform, ironstone gravel and aspect are recognised factors for pine growth.