CARD Project: 032/05VIE Sustainable and profitable development of acacia plantations for sawlog production in Vietnam MS4: Acacia silvicultural guidelines manual Silvicultural guidelines for Acacia plantations managed for sawlog production in Vietnam These guidelines are based on two reviews carried out for the CARD Project 032/05 “Sustainable and profitable development of acacia plantations for sawlog production in Vietnam”. • Review of Acacia genetic resources and propagation methods to support sawlog production in Vietnam (November 2006) • Effects of site management practices and silviculture on productivity of short rotation Acacia plantations in Vietnam - a review (January 2007) It is emphasised that these guidelines are interim and will be revised once more information is obtained through the project. 1. Species and varieties Selected clones of the acacia hybrid (A. mangium x A. auriculiformis) and the best improved planting material of A. auriculiformis (selected clones and improved seed) and A. mangium (improved seed) are best suited for sawlog production. These three options are already proven in this role in lowland regions of Vietnam receiving at least 1000 mm annual rainfall. Acacia. crassicarpa performs well on seasonally flooded sandy soils in central Vietnam. 2. Site preparation In the absence of more specific information, planting holes dug about one month before planting where two-thirds of the hole is filled with a mixture of top soil and fertiliser is recommended. The size of hole is normally 30 cm deep, 20 cm wide at the base and 30-to-40 cm square at the top. 3. Initial spacing The most suitable stocking for pulpwood plantations is between 1111 trees ha -1 (initial spacing of 3 m x 3 m) and 1666 trees ha -1 (3 m x 2 m). The necessity to select final crop trees that meet the requirements of growth rate and form in plantations managed for solid wood suggests that at least 1000 trees ha -1 should be planted where the intended product is solid wood. 4. Fertilizer application Application of fertiliser at planting and six months after planting has significantly improved the growth of Acacia in a number of field trials. The highest dose used to date has been 25 g N, 25 g P and 20.7 g K and 100g micro-organism enriched fertilizer per seedling, applied to Acacia hybrid at planting. It is not yet possible to identify the best fertilizer type for common soil environments or to provide a financial cost-benefit analysis for fertilizer application. 5. Weed control Weed control, either by manual weeding or herbicide application, has been shown to improve stand productivity. At least two weedings per year during the first two years of plantation growth are recommended. After this time, weed growth is suppressed 2 by the development of the tree canopy, at least on the more productive sites. On poorer sites weed control may be necessary for a longer period of time. 6. Pruning # A first-lift pruning should be undertaken at the time of canopy closure and before crown lift has commenced. Trees selected for pruning will be determined by their form, the characteristics of the branches and diameter at breast height. The number of trees pruned will be determined by the distribution of log sizes required at harvest. No more than 30% of the green crown length from below should be removed when the selected trees are lift pruned. Form pruning may be required before canopy closure occurs to increase the numbers of trees that meet the requirements for selection for lift pruning. 7. Thinning # Thinning to stockings lower than that used at planting (at least 1000 trees ha -1 ) is required if the final crop trees are to produce typical minimum required sawlog dimensions. The maximum final stocking will not exceed 600 trees ha -1 . For trees that produce sawlogs of sawlogs 2 m or more in length and with a 200 mm small-end log diameter under bark, lower final stockings will be required. Without thinning, only a very small percentage of final crop trees will produce logs of these dimensions, even on the most productive sites. # Updating the guidelines for pruning and thinning form a key part of the current project 3 . CARD Project: 032/05VIE Sustainable and profitable development of acacia plantations for sawlog production in Vietnam MS4: Acacia silvicultural guidelines manual. guidelines for Acacia plantations managed for sawlog production in Vietnam These guidelines are based on two reviews carried out for the CARD Project 032/05 Sustainable and profitable development. of acacia plantations for sawlog production in Vietnam . • Review of Acacia genetic resources and propagation methods to support sawlog production in Vietnam (November 2006) • Effects of