Abstract
Analysis of historical distribution at more than 30,000 localities shows that higher altitudes were increasingly invaded by alien species introduced into the Czech Republic in the last 250 years. The highly significant effect of the year of record when the effect of the year of introduction is held constant strongly suggests that spread to higher altitudes has become increasingly easier over the last two and a half centuries, a consequence of an interplay of several factors associated with altitudinal gradients in the temperate zone of Europe that were also changing over this period.
These factors were most likely the increasing disturbance associated with greater influence of humans at higher altitudes and increased propagule pressure as well as climate change manifested by an increase in temperature.