cross section of beech trunk with spalting caused by chondrostereum purpureum

artificial attack bark beech black cambium carving caused chondrostereum cross dead discoloration fungus gelderland growth harskamp healthy holz joinery kootwijkerzand lines logs make natural netherlands nonloadbearing ornamental pattern process processed purple purpureum rings sawn section spalting stocked structures such trunk turned used veluwe wood wooden woodturning years