(2005b) tested NIRS calibrations on both faces of SilviScan samples for air-dry density, MFA, MOE, and several tracheid morphological characteristics.
MFA was determined at a 5-mm radial resolution using the X-ray diffractometer unit.
TSLRs were applied to MFA profiles to determine the transition age from juvenile to mature wood for the 127 samples.
where [y.sub.i] is the MFA value of the ith ring from the pith, [x.sub.i] is the ith ring, [a.sub.1] is the intercept of linear fit to data below the estimated breakpoint, [b.sub.1] is the slope of linear fit to data below the estimated breakpoint, [a.sub.2] is the intercept of linear fit to data above the estimated breakpoint, [b.sub.2] is the slope of linear fit to data above the estimated breakpoint, c is the estimated breakpoint, and [epsilon] is the error term.
The transition age seemed to vary between 10 and 40 years for the 127 MFA profiles obtained from SilviScan.
Average values were 431.8 [+ or -] 31.2 kg/[m.sup.3] in BD, 14.1 [+ or -] 2.3 GPa in MOE, and 14.0[degrees] [+ or -] 3.1[degrees] in MFA. The average BD value was similar to that measured by Jessome (1995).
Table 2 presents the calibration statistics obtained for BD, MOE, and MFA by PLS regression.
Good to excellent calibrations were thus obtained for BD, MOE, and MFA. In other words, in this study, strong linear relationships were obtained between the studied wood properties and the absorption values.
Figure 1 shows the correlations between SilviScan data (BD, MFA, MOE) and NIRS values obtained from the calibration and validation sets.
A large part of the variance in BD (85%), MFA (79%), and MOE (88%) was thus explained by FT-NIR spectra.
This random effect was not considered in the development of calibrations that may have influenced the NIRS predictions at the spot scale and was certainly not considered for the MFA profile, which is the most important to determine the transition point.