Impact of stocking and exposure on outerwood acoustic properties of Pinus radiata in Eyrewell Forest.

Authors: M. Grabianowski, B. Manley, J. Walker
Publication: New Zealand Journal of Forestry, Volume N.Z.J.For. 2004, Issue N.Z.J.For. 49(2) 2004, pp 13-17, Aug 2004
Publisher: New Zealand Institute of Forestry

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Abstract: Acoustic measures based on "time of flight" tools such as the Fakopp 2D offer a nondestructive technique for assessing tree stiffness using the fundamental equation E = p V2, where E is the stiffness, p is the green density and V is the acoustic velocity as measured by Fakopp. This study at Eyrewell Forest in Canterbury assessed the variation of stiffness of 27 year-old radiata pine (Pinus radiata) trees planted at different stockings and in two narrow contiguous strips (upwind and downwind) aligned perpendicular to the NW wind.
No significant difference was found between the outerwood acoustic velocity for the two stockings (nominally 100 and 625 stems/ha). However, a significant difference was found between the two strips for velocity and hence estimated stiffness, implying an influence of wind on the acoustic properties of outerwood.
The study indicates a broad range of outerwood stiffness with values lying between 7 and 13.5 GPa. The modest stiffness of the outerwood for the poorest trees is of particular concern when considering that the corewood will be significantly poorer. This focus on within-stand variation contrasts with much current information on wood quality of stands that typically relates to stand average values - and probably only to basic density. In revealing the range of acoustic values found within a single stand, this study draws attention to the opportunity and need to sort material within stands.
The influence of wind appears to affect a "deep perimeter" and managers may need to consider segregating such wood and marketing it separately. At the very least, the noticeable difference in acoustic velocity between the upwind and downwind needs further investigation.

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