Collapse behavior and steam reconditioning of Afares oak (Quercus afares Pomel) and Zeen oak (Quercus canariensis Willd.) from the Akfadou Forest (Algeria)

Zeen oak (Quercus canariensis Willd.) and Afares oak (Quercus afares Pomel), two native Algerian species abundant in the Akfadou forest, yield small-diameter wood suitable for furniture production. However, their industrial utilization is severely limited by their high propensity to collapse during drying. This study addressed this knowledge gap by comprehensively investigating the hygroscopic behavior, shrinkage, collapse development, and hydrothermal recovery of these species. Physical properties, including density, fiber saturation point (FSP), and shrinkage coefficients, were evaluated according to international standards. Additionally, drying and steam reconditioning experiments were performed on 338 defect-free specimens. Steam treatment was applied at 120 °C for 20 min at moisture contents (MC) ranging from 12% to 23%. Results indicate that both species exhibit high density, pronounced volumetric shrinkage, and marked anisotropy, confirming low dimensional stability. Zeen oak displayed greater shrinkage than Afares oak, while both shared an average FSP of 33%. Microscopic observations revealed that collapse developed during drying, primarily associated with ray tissues and anatomical heterogeneity. Crucially, steam reconditioning significantly reduced collapse deformation, especially tangentially, with maximum recovery occurring near 18% MC. These findings confirm both the wood’s vulnerability to collapse and the efficacy of steam treatment in optimizing industrial drying.