evidence: The porcupine’s feeding and gnawing habits can leave negative impressions. Winter feeding on the inner bark of trees can result in timber losses, usually confined to specific areas such as stands adjacent to large denning populations or where porcupines invade young even-age conifers. Winter denning concentrations often occur in rocky and steep terrain where site conditions and access for logging are poor; therefore, trees killed in such areas are relatively unimportant to timber production. Porcupines occasionally cause damage in sugar maple stands, apple orchards, and cultivated crops. If a porcupine chews off an isolated section on a tree’s trunk, the bark will, in time, close over the wound. If a porcupine girdles the trunk, however, the tree will die. Trees with upper branches freshly "barked" (the newly exposed wood shows light against the bark) show that a porcupine is in the area. Beech trees are often damaged only at their bases, perhaps because individuals have a hard time climbing this smooth-barked species. Although porcupines kill a few trees by girdling, most authorities agree the damage they cause over large areas is generally insignificant.