The biomass ofPinus radiata (D. Don) root and shoot systems was measured in a number of studies to determine the effect of stand age and environmental factors on the root/shoot ratio. These and other published studies were carefully assessed to determine firstly those which provide unbiased data for estimating below-ground biomass from shoot data and, secondly, the precision of the root/shoot ratios. Because previous studies were designed for a number of different purposes they were assessed in relation to the methodological requirements that we considered had to be met in order to provide accurate root/shoot biomass information. New data from an effluent irrigation trial at Whakarewarewa Forest near Rotorua, designed to assess the impact of water and nutrient additions on tree growth at stand age 5 years, showed that both the above- and below-ground biomass approximately doubled relative to untreated controls. Consequently, the root/shoot ratio was not significantly affected by effluent type or irrigation rate, and averaged 0.17 across all treatments. At Rangiora near Christchurch, similar results were obtained at an agroforestry trial to assess the impact of moisture and nitrogen supply on tree growth at stand age 5 years, where the mean root/shoot ratio averaged 0.21. These values were similar to the mean ratio (0.20) in a 42-year-old P. radiata stand at Woodhill Forest. Studies of nursery seedlings ready for planting gave lower root/shoot ratios of approximately 0.15, though the root systemshad been trimmed in the nursery. Analysis of published data suggested a wide range in root/shoot ratios in P. radiata, ranging between 0.12 and 0.58 across all studies. However, we observed a number of limitations in some studies which we believe precluded their use for root biomass estimation and prediction purposes. The root/shoot ratio in studies that met the accuracy requirements necessary for our purpose ranged between 0.13 and 0.24, and in typical P. radiata stands the root/shoot ratio averaged 0.19 (95 CI = 0.023) over all ages and sites. The majority of the root system of trees, other than seedlings, was composed of coarse roots and the root stock, and these were largely extracted in studies we considered as suitable. Root biomass procedures generally resulted in the loss of fine roots in most studies, and a slightly increased root/shoot ratio of 0.2 is therefore recommended for carbon estimation in P. radiata stands across all stand ages and sites. This value is consistent with findings reported for various other coniferous species.
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