Introduced pests are not a problem exclusive to a
particular region. Indeed, countries worldwide face
this issue, frequently with the same pests: pests native
to Asia chestnut blight and the Asian longhorn beetle are
problems throughout temperate forests in the Northern
Hemisphere; the genus Phytophthora, in its many
different forms, is currently causing mortality of
numerous tree species in Australia, North America,
Africa, and Europe. Some ecological systems, such as
the tropical forests, are so diverse and complex that
ecologists are still exploring the basic issues of forest
structure and development.