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Establishing the commercial properties of poplar timber in New Zealand – mechanical properties
By Vaughan Kearns, December 2025.
Download TE25-017_Vaughan_Kearns_Ruapehu_Sawmills_Poplar_ingrade_testing_test_results_Ver_2 (pdf)
Executive summary
Objective: To determine the characteristic bending strength and stiffness stresses for thirty samples of rough sawn 100x50mm timber from each of three (3) varieties of Poplar as supplied by Vaughan Kearns of Ruapehu Sawmills.
The three Poplar varieties tested were as follows;
“Toa” a New Zealand bred hybrid poplar that is known for its resistance to rust and leaf spot, and its low
palatability to possums. Toa was commercially released in 1996.
“Eridano” which is a hybrid poplar clone which generally has a strong resistance to common poplar rust is used primarily for soil conservation, shelterbelts and timber
And “Yunnan” is fast growing and often used for shade or shelter trees. It is rust and possum resistant and is able to grow on drier sites.
Density and moisture content measurements were also measured.
Key results
- On the basis of the bending strength the ERIDANO Poplar was marginally stronger than the Toa Poplar, which was in turn stronger than the YUNNAN Poplar. The assignable SG rating based only on the Characteristic Strength was SG 12 for the TOA Poplar, SG 12 for the ERIDANO Poplar, and SG 6 for the YUNNAN Poplar. Combining all 90 test specimens from the three (3) varieties of Poplar the combined structural grade for strength was assigned as being equivalent to SG 10.
- On the basis of the bending stiffness the TOA Poplar was marginally stiffer than the ERIDANO Poplar, which was in turn stiffer than the YUNNAN Poplar. The assignable SG rating limited by the Characteristic Stiffness result was SG 8 for the TOA Poplar, SG 8 for the ERIDANO Poplar, and SG 6 for the YUNNAN Poplar. Combining all 90 test specimens from the three (3) varieties of Poplar the combined structural grade for stiffness was assigned as being equivalent to SG 8.
- The Average moisture content at the time of test was 19.8%
- The average Density at test (using mass at test) was 533kg/m3
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