The objective was to determine the significance of site on preservative depletion from Pinus radiata D. Don and Fagus sylvatica L. 20 x 20 x 500 mm field test stakes treated with a ground contact retention of copper amine plus tebuconazole (CuAz) and copper chrome arsenate (CCA) after approximately 5 years exposure to widely different soil and climate conditions. Site, wood species and their interactions had a dramatic and statistically significant effect on CCA and CuAz-treated pine and beach. Mean Cu depletion for radiata pine treated with 0.72% m/m a.i. CCA after 5.5 years, across 13 sites was less than 1% for above ground portions of stakes compared to 30% for below ground. However, below ground depletions at acidic sites located at a peat bog and a Nothofagus (southern hemisphere beech) forest were 43 and 73% respectively. Mean below ground chromium and arsenic depletions were 9 and 21% respectively but were 22 and 41% at the most severe depletion site (Nothofagus forest). Across all sites, mean above ground depletion of Cu and tebuconazole from radiata pine treated with 0.59% m/m a.i. CuAz, was 19 and 42% compared to 47 and 55% for below ground. Substantially greater loss of copper from CuAz treated wood compared to CCA treated wood, especially for above ground exposure, across all sites, may be significant for wood in service situations where aquatic toxicity of copper is an issue. Beech was more susceptible than pine to loss of copper for both CCA and CuAz. This may have been attributable to less efficient fixation reactions and preservative distribution (macro- and micro-) in beech. The finding that waterlogged sites, and/or sites with low pH caused greatest loss to all treatments irrespective of wood species, in the light of low loss at horticultural sites suggested that the influence of extremes of water availability and of low pH was more important than other mechanisms such as cationic exchange reactions with soil. Particularly high loss occurred at sites where soil was likely to have contained a high organic acid concentration.

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