Improved silvicultural management of Endospermum medullosum (whitewood) for enhanced plantation forestry outcomes in Vanuatu

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Nichols, DJ, Glencross, K, Grant, J, Palmer, G, Smith, RGB, Sethy, M & Viranamangga, R 2013, Improved silvicultural management of Endospermum medullosum (whitewood) for enhanced plantation forestry outcomes in Vanuatu, report to the Australian Centre for International Agricultural Research, ACIAR, Canberra, ACT. ISBN: 9781922137395

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Vanuatu is currently in a period of transition from harvesting native forests to developing plantation resources. One of the most promising species, native to Vanuatu and neighbouring countries, is Endospermum medullosum, or whitewood. This project had as its basic objectives the development of a set of silvicultural guidelines for whitewood, for small woodlots and larger-scale plantations, and preliminary assessment of the wood qualities of plantation-grown whitewood. The project team interviewed 139 landholders in 2008. They found that, in spite of many years of promotion of whitewood as a viable plantation species only 63 ha had been planted in the three major regions of Espiritu Santo Island, though Melcoffee Sawmills has one 17-year old plantation of 270 ha. The primary reason for this failure of plantation establishment is the lack of clearly defined markets for whitewood trees. Many small woodlots were planted but the landholders interviewed had little confidence that planting larger areas would be a profitable activity. The 230 woodlot plantations on Espiritu Santo range up to 20 years in age and provide a guide to the expected growth rates of whitewood in plantation in those areas. Soil and land characteristics were described at more than 40 of these plantations. Growth plots 0.05 ha2 in size were set up in 28 of those sites and measured over four years. These plots indicated mean growth rates of whitewood of approximately 20m3 Soils on Espiritu Santo are highly fertile and productive but there is strong competition with planted trees from the exotic vine Merremia peltata. In a trial comparing plots that were ripped with ones that were not, no difference was recorded in whitewood survival or growth. Further, fertilizer trials on the Lorum site indicated no significant difference in growth of seedlings with fertilizer treatments. Therefore using bulldozers to drive over weeds without major soil disturbance, whilst leaving plant material on the surface, and not using fertiliser can be recommended for large-scale projects. /ha/yr at age 17. Using soil and site assessments and resource mapping it was estimated that around 33 000 ha of land on Espiritu Santo is highly suitable for sustainable whitewood development and is currently not intensively utilised or in native forest. To test the impact of tree spacing on growth and branch development 15 hectares of spacing and thinning trials were established across Espiritu Santo. Two and one half years after thinning significant differences were observed between thinned and un-thinned trees: the annual diameter increment of retained crop trees was 5.6 cm in the thinned plots compared with only 3.5 cm in the un-thinned plots. Recommended density of trees depends on objectives, including whether the landholder is exclusively growing timber or also gardening between rows of trees. The project developed a 50-page silviculture manual which provides guidance on the establishment and management of whitewood plantations. Mixtures of tree species spread the risk of destruction by pests or diseases and can support higher biodiversity than pure monocultures. Two native species were chosen: Flueggea flexuosa, namamau, and Terminalia catappa, natapoa. Nineteen months after planting these two species combined with whitewood had comparable heights and diameters. The durable species F. flexuosa can be harvested after 3-8 years and used for roundwood; whitewood reaches sawlog size in 15-20 years and natapoa can be left to grow on, not only to produce higher quality sawn timber after 25-40 years, but also for continued nut production. Sampled logs from a 17-year old plantation indicated a high percentage (65%) of knotty wood and identified opportunities to add-value to knotty wood by preparing long structural boards and cutting clear sections between defects. An analysis of the value-chain for domestic and export markets and of opportunities for value-adding is being completed as part of an ACIAR-sponsored Masters degree at SCU, by Rexon Viranamangga.