Techniques for Measuring Growth Stress on the Xylem Surface Using Strain and Dial Gauges

Abstract

Growth stress (growth strain) in trees is usually evaluated using either a strain gauge or a dial gauge to measure the strain release. We summarize the techniques used to assess growth stress and compare the two methods. The dial gauge method measures change in distance between two pin targets when growth stress is released by sawing two grooves; from this the strain released is calculated. The absolute values of the strain released depended on whether the two grooves were sawn inside or outside the pin targets: the values in the first case were approximately twice those in the latter. If the grooves were sawn outside the pin targets, the values for the strain released were about the same as with the strain gauge method, in which the strain released by sawing a groove at each end of a strain gauge is measured. The released strain values were consistent when the strain gauge was glued to the outer surface of the secondary xylem after first fully removing the differentiating xylem. To release most of the surface growth stress and maximize released strain values, the optimal distance between the ends of the strain gauge and the grooves cut to release the growth stress was 3 to 5 mm, and the optimal depth of the groove was 5 to 10 mm. Most of the growth stress was released immediately when the grooves were sawn.

Tree growth stress and related problems

“…The surface growth stress can be measured as follows using strain gauges [25][26][27][28][29][30] (Fig. 6).…”

Instrumental method for reducing error in compression-derived measurements of rainfall interception for individual trees

“…The theoretical method outlined within this technical note represents an important development, as hydrologists and foresters currently utilize many forms of strain technology (e.g. Guitard and Castera 1995, Peltola 1996, Yoshida and Okuyama 2002, Moore and Maguire 2005, Murphy et al 2005, Friesen et al 2008, James and Kane 2008 without this level of precision placement.…”

Compression stress in opposite wood of angiosperms: observations in chestnut, mani and poplar

“…They are based on the same principle, which consists in measuring the longitudinal strain at the wood surface, after artificially releasing the stress [15,30]. For chestnuts and mani, the "single hole" method was used [11,15].…”

“…We used the factor 12.3 × 10 −4 corresponding to a standard hardwood. For poplar experiments, RGS was directly obtained using the strain gauge method described by Yoshida and Okuyama [30].…”

“…These values were believed to be measurement artefacts. Indeed, metrological studies showed that the methods for measuring RGS may have a non-negligible incertitude [15,30]. Also, other sources of mechanical stress are a possible cause of error for the estimation of maturation stress.…”