Fast-growth plantation forestry is relatively new in many Southeast Asian countries, and there is a clear need for monitoring and assessment of plantation forest soils in this region. In this study, we used miniature plots to estimate and explain site productivity for three widely planted hardwood tree species: Acacia mangium, Falcataria moluccana and Eucalyptus pellita. Miniature plots investigate forest productivity by carrying out very small-scale, short-term experimental studies and treating the results as analogous to what would occur in an operational-scale forest stand over a normal rotation. Miniature plots were established in three separate compartments of a tropical forest plantation in southeastern Sabah, Malaysia. Plots included the three species of interest, each with a fertilised and unfertilised subplot. Assessments were made of site and soil factors including soil profile properties and laboratory analysis of soil carbon, nitrogen, phosphorus (total and available) and pH. Tree growth was measured for nine months to estimate site productivity. Results suggest the need for research focusing on the role of soil carbon, carbon:nitrogen ratio, available phosphate and possibly soil pH in tropical plantation productivity, as well as the potential for large increases in productivity with high rates of fertiliser. In addition, there were differences in the fertiliser response between species, suggesting that F. moluccana in particular might respond more strongly than A. mangium to high application rates of fertiliser. The results also suggest that miniature plots have considerable potential for monitoring and investigating site productivity in fast-growth tree plantations in Southeast Asia. [ABSTRACT FROM AUTHOR]