Eucalyptus nitens Wood of Spanish Origin as Timber Bioproduct: Fiber Saturation Point and Dimensional Variations

Wood is a primary bioproduct widely utilized as timber in construction and carpentry. Characterization of its properties, particularly moisture response, is essential for industrial performance. The Fiber Saturation Point (FSP) influences the dimensional stability and efficiency of industrial processes such as drying. This study determines the maximum dimensional variation and the FSP of Eucalyptus nitens solid wood from plantations in Northwestern Spain, studying 354 specimens of 20 × 20 × 50 mm. Mean and median values were calculated considering and omitting outliers. Additionally, a graphical FSP value was obtained by applying the statistical theory of the center of gravity, defined as the intersection of lines derived from the two-dimensional data distribution. For maximum dimensional variation, the analysis yielded mean values of 5.2% [±1.53] and 11.2% [±2.84] and medians of 4.8% and 10.4%, in radial and tangential directions, respectively. The mean FSP was 29.9% [±7.95], the median 28.9%, and the graphical estimate 30.8%. Establishing the FSP defines the critical moisture threshold at which significant changes in physical and mechanical properties, as well as dimensional alterations, occur in this bioresource, particularly for its use as a bioproduct in carpentry and construction or for industrial wood drying.