Effect of initial spacing on first thinning product recovery, and financial outcomes in whitewood (Endospermum medullosum) plantations in Vanuatu

This paper investigates the products from first thinning at age 6 in Endospermum medullosum(whitewood) plantations in Vanuatu at three stocking densities, and the financial outcomes from several silvicultural thinning regimes based on these spacings. Whitewood plantings established at stockings rates of 417, 625 and 833 stems per hectare were thinned at age 6 to approximately 45 % retained basal area. The thinning products were measured during harvest and value was estimated based on costs of production and appropriate margins relative to radiata pine products already on the market. Financial modelling for the whole rotation was undertaken for each of the spacing and thinning scenarios in the trial. The volume and size of poles and posts at first thinning was related to spacing. Low stocking density produced smaller quantities of larger poles, whereas higher stocking densities produced larger quantities of smaller posts. However, the monetary value of larger products grown under lower stocking rates was less than the value of the greater volume of product at higher stocking rates. This greater volume at higher stockings resulted in higher NPV for regimes with higher initial stockings for modelled scenarios regardless of harvest age. An exception was a scenario where no market for thinnings is available. A direct silvicultural regime (i.e. one with low planting density and no thinnings) had the highest NPV due to the higher price per cubic metre of larger diameter logs, achieved more rapidly because thinning did not remove basal area. Where thinning products are marketable, higher initial planting densities provide higher returns. Where access to markets for thinning products is difficult or where infrastructure is expected to improve in the future, planting at low stocking and without any thinning provides a high return on investment.