Local species and populations ensure a certain
degree of adaptedness, since the population genetic
structure reflects the fluctuations in local environmental
forcing functions. In contrast, numerous examples
demonstrate the dangers of using unadapted species
and provenances. Even comprehensive species and
provenance trials may lead to erroneous conclusions,
since not all parameters affecting survival and productivity
(mostly extremes) are encountered during the
period of testing. A major weakness is that the testing
period is too short compared with the rotation age of
the species. Further, species and provenance trials normally
cover only a small number of potential sites,
making spatial extrapolation of the results rather uncertain.
As a consequence, introduced species and provenances
often contribute to a reduced system stability
due to lack of adaptedness (resistance). Changes in the
environmental forcing functions caused by climate
changes and the introduction of exotic alien organisms
(pests) may drastically reduce adaptedness of local
species and populations.