Evaluating growth strain of Eucalyptus globulus Labill. from SilviScan measurements

Longitudinal surface strain was measured or estimated using three different methods along the stems of nine trees of 10-year-old Eucalyptus globulus Labill. Wood samples were collected close to the location where the strain was measured or estimated. Microfibril angle (MFA), cellulose crystallite width (W-cryst), microdensity and Young's modulus along the grain (E-L) were determined using the SilviScan-2 technology at high spatial resolution. Relationships of measured strain and estimated strain to wood properties were established. The quality of the relationships depends on a particular wood property. Strain was more closely related to mean W-cryst than to any other wood properties. Its relationship with MFA was the next closest. Based on the results of regression analysis, we propose that W-cryst may be suitable for the prediction of surface strain at a moderate level of reliability. Adding measurement of MFA, microdensity and E-L does not significantly improve the prediction quality. The strain measurement method also affects the results. The best relationships were obtained with longitudinal displacement measured by the CIRAD method. Strain measured by the strain gauge method gave weak relationships, possibly owing to variation in the cambium age of the specimens.