Don’t blame the tree volume equations

Authors: Richard Woollons
Publication: New Zealand Journal of Forestry, Volume N.Z.J.For. 2014, Issue N.Z.J.For. 59(3) 2014, pp 37-39, Nov 2014
Publisher: New Zealand Institute of Forestry

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Abstract: When predicted and actual clearfall volume per hectare estimates differ appreciably in a region, it is common for the applicable tree volume equation to be blamed for the discrepancies. Here it is argued that provided the volume function is well constructed and stands are adequately sampled, then total volume per hectare can be confidently estimated to within five per cent – too small an error to account for the outcome of many reconciliation studies. The problem An important study for many forest organisations is a comparison of predicted and realised volume yields. Estimates are made of net predicted volume per hectare as estimated from inventories or growth models, and the corresponding realised volume assessed by weighbridge tonnes converted to a volume estimate. There is a very reasonable question in relation to management – to what extent do the two figures agree? The trouble begins, at least for forest researchers responsible for the volume equations construction, when two estimates differ substantially.

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