9. RATIONALE AND KEY RESEARCH QUESTIONS ADDRESSED BY FIELD TRIALS ESTABLISHED AS PART OF THE ACIAR SMALLHOLDER TREEFARMER PROJECT John Herbohn, Nestor Gregorio and Jerome Vanclay A series of field trials have been established as part of the ACIAR Smallholder Tree Farmer Project. These trials are designed to have both a research and demonstration function. A field trial was designed to investigate the potential interaction between four species providing a combination of native and exotic species and nitrogen-fixing vs non-nitrogen-fixing. Importantly, this design provides information about different mixture ratios using only one plot. This field trial will provide important information about the interactions of the four species when grown in varying mixture ratios. A clinal trial using the design of Vanclay (2006) was established in Leyte Leyte in December 2007 using four species. This trial will provide important information on ideal spacing at which trees should be established and how initial planting density affects site capture and early growth, especially in respect to indigenous species. Field trials have also been established to investigate the effect of fertiliser and shade on the establishment and early growth of mayapis and to demonstrate the positive impact that the use of high quality germplasm and good early age silviculture has on the growth of gmelina. The establishment of the field trials has been an important capacity building exercise within the project team. Filipino collaborators have been intimately involved in the design, establishment and monitoring of the field trials and are now capable of establishing similar rigorous field experiments. INTRODUCTION Analysis of the tree inventory database indicates that on average only about 30% of site potential in terms of timber yield is being captured by smallholder tree farmers in Leyte. This suggests that substantial improvements in timber yields, and hence financial returns, could be made with improved silviculture. However, there is a lack of locally-relevant evidence- based silviculture prescriptions for key species, including Gmelina arborea Roxb. and Swietenia macrophylla King., especially in relation to the likely impacts of the two key silvicultural practices of thinning and pruning of mature stands in Leyte. There is also a lack of rigorous field trial data for many other species of interest to smallholders. In particular, there is great interest in indigenous timber species but few evidence-based recommendations on what species offer the greatest potential and how these species should be grown. The field trials were designed to investigate ways to improve the performance of existing plantations, and design better performing tree farm systems for new plantations. Field trials established as part of ACIAR project ASEM/2003/052 – Improving Financial Returns to Smallholder Tree Farmers were required to serve both research and demonstration functions. This requirement has a number of implications and constraints. First, the sites need to be highly visible and accessible, hence all sites have been located adjacent to roads. This requirement resulted in difficulty in obtaining suitable sites and some compromises had to be made in terms of total area available for planting. Second, the species studied had to be of high interest to smallholders. Third, for existing plantations, only two species have been planted widely (gmelina and mahogany) and hence research on 67