What makes exotic pest species so dangerous?
Tree species that are present in a region, country or continent have evolved over thousands of years into their present form. Meanwhile, the indigenous insects and diseases associated with these “host” trees have evolved along with them, and so have diseases, parasites and predators of these various insects and diseases. After evolving together for many years, all of these ecosystem components have reached a state of equilibrium. The adaptation of trees occurs on a scale of centuries. By contrast to insects and fungi that produce one or two generations every year, trees begin to reproduce at an age varying between 15 and 60 years, depending on the species. After that, a tree produces seeds every year or at intervals of 2, 3 or 5 years. It takes trees longer than herbaceous plants, insects and fungi to adapt to changes. The arrival of an exotic pest species disrupts the ecosystem balance that has evolved over hundreds of years. Trees lack defense mechanisms against these new pests and a
