Establishing, pruning and thinning Acacia plantations to increase wood value doc

Establishing, pruning and thinning Acacia plantations to increase wood value CARD Project VIE:032/05 Sustainable and profitable development of Acacia plantations for sawlog production in Vietnam 10-year-old-thinned stand of A. mangium in Indonesia. Average diameter was 36.6 cm and total stem volume was 228.7 m 3 / ha. Final stocking was about 230 stems/ha and stand basal area was about 24 m 2 /ha. An example of a well-managed stand. Acacia managed for sawlogs • Singling is undertaken around age six months after the seedling has become well established. Singling ensures that the tree starts growing with a single stem. Single stems are essential for sawlog production • Pruning is undertaken to increase the value of the log: the wood formed after pruning is knot-free wood (clear wood) • Lift pruning removes branches from ground level upwards • Form pruning removes branches that will potentially lead to reduced stem straightness. This type of pruning is done several months before lift pruning in the same section of the stem Principles of singling and pruning • Multi-stemmed trees • Persistent branches • Poor form • Knots • Potential heart rot Therefore singling, pruning and thinning essential Issues in Acacia plantations managed for solid wood • 3-year-old Acacia hybrid clonal plantation on fertile site near Hue • Note the large number of double leaders and unpruned branches • Singling at age 4-6 months is an essential first step for producing sawlogs, and adds value to pulpwood plantations Acacia hybrid plantations in Vietnam • Dead branches are associated with wood discoloration and decay • Green pruning prevents development of loose knots and decreases the size of the knotty core HOWEVER • Removing green (live) branches reduces productive capacity of tree BUT • The remaining leaves on the tree work harder after green pruning! Why green pruning? • Slower-growing species are more affected than faster- growing species What proportion of branches can be removed without affecting growth? % of crown length removed beyond which growth is reduced Acacia mangium 40% (fast-growing) Acacia melanoxylon (slow growing) 25% • 3 x 3 m between- and within-row spacings • Pruned at age 18 months Indonesian experiment on Acacia mangium The treatments Control • Unpruned • No singling Lift pruning • Singling • 25% crown length removed from ground level Form pruning • Singling • 25% crown area removed to 3 m height • Branches removed were competing, large, or at narrow angle • No difference between form and lift pruning • Controls significantly smaller because multi-stemmed • No differences in crown lift response to pruning at 18 months - Acacia mangium in Indonesia 0 2 4 6 8 10 unpruned form-pruned lift-pruned Height (m) and diameter (cm) height diameter Growth response 18 months after pruning [...]... at typical pulpwood stockings of 1000-1600 trees/ha, even on the most productive sites • It is difficult to grow sawlogs on poor sites which support basal areas below 20 m2/ha Acacia hybrid thinning trial at Dong Hoi • Objective was to determine the growth response of Acacia hybrid to different levels of thinning and how to use thinning to maximise both wood volume (basal area) and wood value (log size)... 600 450 300 Stocking following thinning at 2.5 years Practical issues for farmers and extension agents - pruning • Form and lift pruning cannot be done using machetes as dead branch stubs will remain and cause defects in the timber • Tools for pruning are long-handled shears (cost $50+ for good quality), hand shears ($20+) and pruning saws ($10+) • Look after the tools Keep them sharp and prevent rust... the tools, or does each farmer need one? Acacia hybrid plantations in Vietnam • Lift pruning 2year-stand at Dong Hoi • Note green branches • Note careful pruning technique Always prune flush with branch collar and with no branch stub remaining Practical issues for farmers and extension agents - thinning • Farmers may be reluctant to thin stands because of perceived loss of wood volume and sales • If thinning. .. of thinning should ensure that branches remain green for pruning, but do not get too large • A first thinning to waste may be needed • Thinning regime should maximise value of thinned and final-crop trees Financial models for sawlogs and pulpwood Discounted cash flow model for one hectare of pulpwood plantation Acacia hybrid all costs and returns in US dollars Spreadsheet financial model for pulpwood... This is part of the thinning strategy Thinning Trial at Dong Hoi (600 stems ha-1) 5 22 34 20 19 35 24 4 11 3 12 26 13 27 1 32 18 15 29 Acacia hybrid thinning trial at Dong Hoi – 300 trees/ha plot after thinning and pruning Diameter and basal area response to thinning at Dong Hoi dbh and basal area 13 months after thinning, Dong Hoi Critical difference (P . Establishing, pruning and thinning Acacia plantations to increase wood value CARD Project VIE:032/05 Sustainable and profitable development of Acacia plantations for sawlog. determine the growth response of Acacia hybrid to different levels of thinning and how to use thinning to maximise both wood volume (basal area) and wood value (log size) • Initial spacing. • Pruning is undertaken to increase the value of the log: the wood formed after pruning is knot-free wood (clear wood) • Lift pruning removes branches from ground level upwards • Form pruning