And diversity is a good thing. Randall points out that insects and other small animals need a variety of native plants to feed on. Exotic pests can cause damage too. The balsam wooly adelgid has killed Fraiser firs in the North Carolina mountains. This sap-sucking insect can kill a tree in five to seven years, White says.
Trees are even more susceptible to pests when stressed by air pollution.
Hugh Morton, a Carolina alum and owner of Grandfather Mountain, has often spoken out about the deadly mix of air pollution and adelgids. The balsam wooly adelgid, originally from Asia, traveled to North Carolina in the 1930s attached to some balsam fir trees from New England. Since North Carolina trees have had no past history, or coevolution, with the pest, their defenses against it are low. A similar insect, the hemlock wooly ade-lgid, has now moved into North Carolina and is threatening hemlock trees in the mountains. Other plants have been damaged by a somewhat larger exotic animal the European wild boar.