Đề tài Nghiên cứu khoa học acacia plantations for sawlog production- Some sivilcultural measures and recommended suitable and profitable acacia species

Collaboration for Agriculture and Rural Development (CARD) Program 186 ACACIA PLANTATIONS FOR SAWLOG PRODUCTION: SOME SIVILCULTURAL MEASURES AND RECOMMENDED SUITABLE AND PROFITABLE ACACIA SPECIES Project title: Sustainable and profitable development of acacia plantations for sawlog production in Vietnam Project code: CARD 032/05 VIE Authors: Phi Hong Hai1*, Chris Harwood2, Chris Beadle2, Sadanandan Nambiar2, Khongsak Pinyopusarerk2, Vu Dinh Huong3, Dang Thinh Trieu4, Pham Xuan Dinh5, Trieu Thai Hung5 Project Implementing organisations: 1 Research Centre for Forest Tree Improvement - FSIV 2 CSIRO – Sustainable Ecosystems, Private Bag 12, Hobart 7001, Australia 3 Sub-Institute of Forestry Research in the South - FSIV 4 Silvicultural Technical Division - FSIV 5 Center for Forestry Science and production in Northern Central regions - FSIV * Responsible author (phi.hong.hai@fsiv.org.vn) SUMMARY Studies on thinning response to diameter growth, pruning response to log defects and response to phosphorus (P) of acacia hybrid growth in Quang Binh and Quang Tri showed that: (1) thinning method increased diameter growth of acacia hybrids; (2) pruning decreased log defects of acacia hybrids; (3) fertilisation of 10 g of elemental phosphorus (as 143 g superphosphate/tree) at planting time was sufficient for increasing of height grow of acacia hybrids at early stage in Quang Tri. In sawn timber plantations, Acacia mangium, A. auriculiformis, A. crassicarpa and Acacia hybrids (A. mangium x A. auriculiformis) were proved to be suitable species. A. crassicrapa was a promising species and performed well in inland sands in the central Vietnam. A. mangium was a suitable species in lowland in the northern Vietnam. While, A. auriculiformis was preferred planting in the southern Vietnam. Acacia hybrids could be planted in many sites from the North to the South. National clones, and technological advanced clones that approved by Ministry of Agriculture and Rural Development were suggested for using in commercial plantations of A. auriculiformis and acacia hybrids. For A. mangium and A. crassicarpa, seed sources from seed production areas and seed orchards were recommended to use. 1. Introduction Needs on timber for processing industry in Vietnam in 2010 is expected to be 9.35 million m3 (MARD, 1999). But now the natural forests are limited for exploitation, so the annual timber volume from this kind of timber sources will only provide less than 300,000 m3 per year (MARD, 1999). Timber from plantation forest and imports is expected as the compesating source for this deficit. To meet the demand of industrial wood and to increase forest coverage to 43%, the reforestation program has planned to plant 5 million hectares of forest by 2010. Among them, more than 2 million hectares are production forests, this source can provide industrial wood. Increasing forest productivity through improved seeds and silvicultural techniques will play a crucial role to meet the demand for CARD 032/05 – Acacia planation for sawlog production 187 timber and and to reduce the volume of imported wood. Acacia species have been imported into Vietnam since middle of 20th Century, mainly from Papua New Guinea (PNG) and Queensland, Australia (Nguyen Hoang Nghia, 2003). In Vietnam, in 2005, the total area of acacia plantation reached 400,000 hectares, including 200,000 hectares of acacia hybrid (Ha Huy Thinh, 2005). Productivity and sustainability of plantation of Acacia species are crucial to improving the country's economy, the development of rural areas, and the creation of pulp and sawlog. The CARD project 032/05 VIE titled “Sustainable and profitable development of acacia plantations for sawlog production in Vietnam" was implemented from 2006-2009 by a research collaboration between the Forestry Science Institute of Vietnam and the CSIRO, funded by the Collaboration for Agriculture and Rural Development (CARD) Program. The project applied a diversified approach, combining research to improve breeds, site and forest management, and economic evaluation. Assessment of improved varieties for Acacia has been made to identify the acacia species suitable for plantion for sawlog production, and other propagation techniques suitable for these varieties. Besides, silvicultural techniques for reforestation and forest management have also been evaluated by this project. In addition, two trials evaluating appropriate silvicultural techniques have been built at the Central region. The first is thinning trials to assess the impact of thinning technique on diameter growth, thus helping increase the diameter enough for sawlog requirements. The second is sustainable silvicultural trials to test the long- term effects of different site management techniques on sustainability of forest productivity over several forest rotations. This paper summarises some key results from thinning and pruning trials and testing sustainable silviculture. Also, the evaluation of improved varieties for Acacia and silvicultural techniques for acacia plantation, as well as suitable Acacia species for sawlog production are also discussed and recommended. 2. Research materials and methods 2.1 Thinning and pruning trial A mixed plantation forest of hybrid acacia clones of 2.5 years old in Dong Hoi - Quang Binh has been selected for thinning trial. Plantation model was built in December 2003, with a mixture of the hybrid Acacia clones BV10, BV16 and BV32. The trees in this model are remarkably of good growth and good form. The plantation is well stocked (1000 trees/ha), healthy, average height of trees reached 8 meters, and crown lift is minimal. With this growth rate, it is predicted that forest productivity is 20m3/ha/year for a pulp production rotation. For all these reasons, this plantation already meets the criteria that define an ideal site for managing an Acacia stand for solid wood. Thinning response trial was established in June 2006. Four thinning treatments, including the control (unthinning) has been used in the study (Table 1). The basic design of the trial is randomized complete block, with four replications. All the trees in the experimental treatments were pruned to 2.3 m from the root. Pruning is carried out carefully so that the stems are cut close to the original branch and not harmful to the original branch. Lift prunning in the Dong Hoi thinning trial P.H. Hải, C. Harwood, C. Beadle, S. Nambiar, V. Đ. Hưởng, Đ. T. Triều, P.X. Đỉnh, T. T. Hưng 188 Table 1. Thinning treatments and plot sizes at Dong Ha Thinning Trial Treatments (Stems/ha) Gross (Trees /plot) Net (Trees /plot) 1000 (unthinned, control) 63 35 600 38 21 450 28 16 300 19 11 Plot size (ha) 0.063 0.035 Dimensions (m × m) 28 × 22.5 20 × 17.5 2.2 Sustainable silviculture demonstration trial A site for the silvicultural trial was chosen at Dong Ha - Quang Tri, managed by the Science Center and North Central production - Forestry Science Institute of Vietnam, to establish sustainable silvicultural trials for long-term track . This site was planted with hybrid Acacia, with the yield of 19 m3/ha/year at the 9th year. After extraction, the area was fenced off to avoid the effects of animal grazing. Leaves and twigs after the first pruning is kept on the site. Soil analysis results before planting showed that the soil at this site is degraded, with low total nitrogen, phosphorus and pH. Six hybrid acacia clones (BV10, BV16, BV32, BV71, BV73 and BV75), being the national seed and technical advance, have been used to establish the sustainable silvicultural trials. The experiment was designed in randomized complete block (5 experimental treatments and 4 replicates). The experimental plot size is 21.5 x 20 m (6 rows x 10 trees/row). Experimental plots are separate from one another by three rows of trees in both dimensions. The experimental treatments are as shown in Table 2 to examine the impact of the increase in the amount of phosphate fertilizer to the increase in stem diameter, and the effectiveness of different weeding methods (method of using herbicides Roundup and manual weeding two times per year). The amount of phosphate fertilizer for each plant was determined from analysis of soil and leaf nutrient testing before establishment of the siviculture experiment. 2.3 Record keeping and statistical analysis Records on both thinning trial and sustainable silviculture experiment are kept and assessed every six month beginning from thining activity and plantation. Diameter at breast height (Dbh) and height (Ht) of all trees in each experimental plots were collected. The statistical analysis was processed on the average value plots and using mathematical fixed-effects model, where the replicate blocks and the experimental treatments are considered constant. Measuring stem taper in the Dong Hoi thinning trial CARD 032/05 – Acacia planation for sawlog production 189 Table 2. Experimental treatments applied for siviculture trial in Dong Ha Treatment ID Nutrition treatment Vegetation management T1 Control – no fertilizer Pre-planting herbicide spray and two sprays per year to give complete weed control, with a rate of 4l ha-1 Roundup herbicide per application T2 P1 10 g elemental P applied as superphosphate T3 P2 20 g elemental P applied as superphosphate T4 P3 (=P2 + 10 g K per tree applied as potassium sulphate) T5 Control – no fertilizer No herbicide application. Two hand weeding per year as per standard practice at Dong ha Station 3. Research results and discussions 3. 1 Impact of thinning on individual tree diameter Results of demonstration pruning trial in Dong Hoi, Quang Binh have confirmed that pruning can improve growth in diameter of the Acacia hybrid in the trial. After 2 years of thinning, the trees in the trial plot reached an average diameter at breast height of over 16cm, while the trees in control plots (no thinning) has the diameter of 14.5 cm (Table 3). The individual tree diameter and wood volume in the treatment plots of thinning down to 300 stems/ha and 450 stems/ha are larger than that in the plot of 600 stems/ha, but the phenomenon of tree top fracture and early separation of stems is quite common. Therefore, thinning down to the density of 300 stems/ha and 450 stems/ha is not suitable for sawlog plantation. Table 2. Individual tree growth and stand basal area 24 months after thinning treatments imposed, i.e. stand age 4.5 years, in the trial at Dong Hoi, Quang Binh Thinning treatment (stems/ha) Tree height (m) Diameter at breast height (cm) Basal area (m2/ha) % woodvolume 300 16.8 17.1 7.4 28 450 17.2 16.3 9.6 23 600 17.3 15.9 11.9 19 1000 17.2 14.5 14.1 7 Statistical error none P<0.001 P<0.001 P<0.001 Basal area in the 600 stems/ha treatment (11.9 m2/ha) is not much lower than that of the unthinned control plot 1000 stems/ha (14.1 m2/ha) (Table 3), i.e. the total wood volume in the 600 stems/ha treatment is little lower than that in the unthinned control plot. The calculations based on full field measurement shows that the proportion of timber can be used for sawlog (Mean diameter at breast height ≥ 15cm) in the 600 stems/ha treatment is 19%, while it is only 7% in unthinned control plots. Thus, the thinning treatments have created a proportion of wood with suitable diameter for sawlog much higher than where the thinning is not conducted. Prices of sawlog are usually double the normal prices of pulp wood, so the value wood sale from the thinned plots may be equivalent to the unthinned plots, even after over four years of plantation. If the tree that have been pruned can be sold as pulp wood, the total value of the 600 stems/ha plot will be higher than that of the control plots, and the profitability could be even higher when exploiting at the age of 6-7 years old. P.H. Hải, C. Harwood, C. Beadle, S. Nambiar, V. Đ. Hưởng, Đ. T. Triều, P.X. Đỉnh, T. T. Hưng& P.Khongsak 190 Most of Acacia forests in Vietnam were planted with initial density from 1000 to 1600 stems/ha (i.e. planting distances 4 x 2m, 3 x 3m, 3 x 2.5 m and 3 x 2 m) (Nguyen Thi Lieu, 2004; Pham The Dung, et.al, 2005; Vu Dinh Huong et. al, 2006; Nguyen Huy Son et. al, 2006; Nguyen Duc Minh et. al, 2004). The thicker density, the stronger competition between the trees in the forest. Therefore, early pruning is very important to promote growth in diameter of the trees in the forest. On the well- established forest site, if the good seeds are planted with appropriate silvicultural management, including weeding and fertilizing, the by-product from pruning at the age of 2.5 to 3 years old can be sold as pulp wood, and the remaining trees can provide sawlog after a short-rotation of 5-6 years. 3. 2 Impact of thinning on tree defect A sawing study was conducted on logs to study the effects of pruning on tree defect. 15 thinned trees from thinning treatment plots and 15 unthinned trees from the surrounding plantation (at the same age) were cut down. The two sets of trees were matched for size and covered the range of log diameter large enough for sawing (dbh over bark range from 20 cm upwards. Butt logs of 2 m in length were sawn on a bandsaw to produce from 4 to 6 boards per log, of about 30 mm in thickness. Defects (mostly associated with branches and associated dead and discoloured wood) were marked on each board. All boards were photographed. The numbers of defects in the outer wood, laid down after pruning, and the inner wood laid down before pruning were scored (Table 4). As expected, the average number of defects on the inner part of the game is similar between the trees is not pruning and pruning trees (4.9 and 5.0, respectively). Because the inner timber boards were formed before pruning is done. In contrast, the planks are sawn from the tree pruning is 0.5 defects / Snowboarding at the outer boards, while boards from tree pruning is 1.2 defects / boards. Such pruning trees have fewer defects than. Handling changes to test the effects of pruning to defects in the outer wood planks showed clear differences (P <0.001). Boards from unpruned tree No. 3 Boards from pruned tree No. 5 Inner-wood defects in boards from pruned tree no. 11 Table 4. Number of defects per board in the outer and inner wood, for pruned and unpruned logs Parameter Unprunedlogs Pruned logs Significance of treatment effect Diameter at breast height (cm) 21.3 19.5 not significant Knotty core wood 5.0 4.9 not significant Number of defect in the outer wood 1.2 0.5 P<0.001 The results of this study can draw two conclusions as follows: (1) First pruning to be conducted at the age of 2.5 years, when the diameter at breast height reaches 9.5 cm to avoid defect in the outer wood. At the age of 3.5 years, pruning to be conducted for second time. The unpruned trees have higher defect rates in the outer wood, created by branches CARD 032/05 – Acacia planation for sawlog production 191 causing death knotty core on the surface of sawn boards. (2) First pruning should be done earlier, when the lower branches of a tree are alive. Such pruning associated with pruning dead branches will avoid the small defects on the sawn boards. However, the good combination between early pruning to remove the defects and the risk of limited growth rate due to pruning activity should be noted. If the tree diameter at breast height is 7 cm and its height is 7 meters, it is needed to prune to a height of just 2.4 meters above the ground, meaning that pruning reduces one third of tree canopy (assuming that there is no phenomenon self-trimmed canopy). The experiments are being conducted in the framework of ACIAR project FST 2006/87 and will provide a more complete pruning appropriate time. 3.3 Impact of phosphate fertilizer on growth of the tree Sustainable silvicultural trials in the Dong Ha experimental station in Quang Tri have been successfully conducted, with survival rate of over 80% in all plots at 24 months old. Growth of hybrid acacia in all 3 experimental treatments with phosphate fertilizer application is significantly faster than the growth in two control treatments for the control (Table 5). Silvicultural sustainability trial in Dong Ha, 10 months after planting, showing growth difference between unfertilized (left) and fertilized (right) plot Clear impact of phosphate to the growth of hybrid acacia in the age of 2 years has been demonstrated. The average height of hybrid acacia in the second rotation is approximately 7 m at 2 years old and is considered quite promising in the treatment of supporting phosphate fertilizer at Dong Ha, Quang Tri. The difference between the control treatment and phosphate fertilizer application is clear and the differences at 1% (P <0.001). Supporting 10 g of phosphate elements (of the superphosphate) may be enough to impact positively on growth in height in the early stages, on the poor soil and actually more sustainable than the previous rotation. Fertilizer application amount is equivalent to 143 g of superphosphate per tree or 200 kg of superphosphate / ha. Explaination of the positive effect of phosphate to the growth of hybrid acacia is probably because Acacia species are capable of nitrogen fixation and nitrogen fixation process have a positive reaction from elemental phosphorus fertilizer (Vance et al., 2002). Then phosphate fertilizer also improves nitrogen for Acacia hybrid and help plants grow better. Moreover, Vu Dinh Huong et. al, 2004 concluded that setting up site management (soils and the fall) is significance between business rotation to ensure sustainability of A. auriculiformis planted forest. Leaves and twigs from the first lumber is kept on site. Impact on the land is minimised. Leaves and twigs will create a thin layer of topsoil protection. This management measures is contrary to the traditional methods which are being applied (vegetation is burned and fully plowed). Traditiona management measures would lose the organic matters, nutrients and increase soil erosion, thereby reducing forest productivity and water pollution (Nambiar, 1999). P.H. Hải, C. Harwood, C. Beadle, S. Nambiar, V. Đ. Hưởng, Đ. T. Triều, P.X. Đỉnh, T. T. Hưng& P.Khongsak 192 Table 5. Survival rate, Diameter at breast height (Dbh) and Height (Ht) of Acacia hybrid in sustainable sivilcuture experiment in Dong Ha after 2 years of age Treatments Ht (m) Dbh (cm) Survival (%) Control – no fertilizer 6.16 7.47 80.0 P1 10 g elemental P applied as superphosphate 6.98 8.57 80.4 P2 20 g elemental P applied as superphosphate 6.95 8.53 76.3 P3 (=P2 + 10 g K per tree applied as potassium sulphate) 6.89 8.70 82.1 Control – no fertilizer 6.41 7.88 80.0 Statistical significance P<0.001 P<0.001 none Standard error 0.15 0.23 3.4 Recommendation of suitable Acacia species suitable for sawlog production In Vietnam, Acacia mangium, Acacia crassicarpa and Acacia auriculiformis show best grows in testing of tropical Acacia species (Le Dinh Kha, 2003). A. crassicarpa is a promising variety for sawlog production but it has not been proven yet. A. auriculiformis grows too slowly to be considered for profitable sawlog-producing plantations in northern Vietnam, and acacia hybrid and A. mangium are therefore preferred for sawlog production in the lowlands of northern Vietnam. A. mangium is not favoured by production enterprises in the south of Vietnam, who consider it to have inferior wood quality and susceptible to wind damage. They prefer to plant A. auriculiformis and acacia hybrid. There may be differences in wood quality of A. mangium grown in northern