Diameter growth rates of beech (<i>Nothofagus</i>) trees around New Zealand

Authors: Sarah J. Richardson*, Jennifer M. Hurst, Tomás A. Easdale, Susan K. Wiser, Alan D. Griffiths, Rob B. Allen
Publication: New Zealand Journal of Forestry, Volume N.Z.J.For. 2011, Issue N.Z.J.For. 56(1) 2011, pp 3-11, May 2011
Publisher: New Zealand Institute of Forestry

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Abstract: Beech (Nothofagus) accounts for a large proportion of the privately owned indigenous forest in New Zealand that is available for timber production. In order to develop management plans for those beech forests there is a need to refine our knowledge on tree growth rates and to take account of tree size, local competition and regional differences. In this article, we use a large dataset on tree growth in unmanaged forests throughout New Zealand to develop size-specific growth models for the four beech species. In particular, we model both normal (“average”) and above-average (“rapid”) diameter growth rates. We found that average tree diameter growth rates were typically between 1 and 3 mm/yr and rapid tree diameter growth rates ranged between 1 and 5 mm/yr. For stems under 500 mm diameter at breast height, hard and red beech typically grew faster than black-mountain and silver beech. However, for larger trees, the fastest rates were found in black-mountain beech in Southland and silver beech in Nelson-Marlborough. Growth rates of >= 10 mm/yr were extremely rare in our dataset and accounted for <0.2% of all trees (27 out of 17,781 trees). Data from thinning trials show that beech trees can achieve growth rates in excess of 6 mm/yr, making a compelling case for further stand thinning to enhance the generally slow growth rates of beech in unmanaged forests.

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