Wood Quality of Silver Fir Affected by Heterobasidion spp. in Pure and Mixed Forest Stands in Mediterranean Mountain Forests

This study aimed to evaluate whether the mixing of tree species, with a focus on beech (Fagus sylvatica L.) (FS) and silver fir (Abies alba Mill.) (AA) in pure and mixed stands, could improve the quality of wood products and biomechanical characteristics. The hypothesis was that silver fir in mixed stands, less affected by Heterobasidion spp. Roots, would yield higher-quality woody materials. The study area is in Southern Italy, in Calabrian Region, at an altitude between 900 and 1.200 m a.s.l. Non-destructive methods (TreeSonic timer) estimated the Dynamic Modulus of Elasticity (MOEd), while infrared spectroscopy (TF-IR spectrometer) measured molecular components like lignin and cellulose. A Linear Discriminant Analysis (LDA) clustering model was applied. Furthermore, a model based on linear discriminant analysis was developed in Python to distinguish different forest types based on the infrared (IR) spectrum. Results revealed complex interactions in mixed stands, where despite smaller tree diameters, both silver fir and beech benefited. Silver fir in pure stands faced higher Heterobasidion spp. infestation, impacting wood quality. Mixed stands showed more regular tree growth trends, enhancingwood quality, supported by higherMOEd, cellulose, and lignin levels. Forest management promotingmixed forests appears to enhance wood quality and commercial timber value for the studied species. Further studies will determine whether the general positive effects of mixing silver fir and beech can be generalized to other species of forest interest.