Since BRR disease causes root rot at the lower trunk above grade level (e.g. it could be observed up to 2 m in some tree species) and/or root collar and/or roots at the sub-soil level, it is essential to evaluate the thickness of sound wood of the tree at horizontal plane at critical levels (i.e. area showing decay and/or specific signs/symptoms of BRR disease) of the lower trunk, as well as at the trunk base, through the use of tomography and/or resistography. For sub-soil level evaluation, the trunk base or even at lower levels (e.g. after soil excavation using spade and/or air spade without affecting tree stability) could be assessed using resistography drilling at an angle (45 degree) downwards which could provide some indication on the relative soundness of tree roots.