The magnitude of biological invasions is increasing world-wide. Areas affected by alien plant invasions are continuously expanding and the extent and complexity of their impacts are increasing.
“If you can't measure it, you can't manage it” is, as with all such well-worn phrases, only partly true. But to adapt another such maxim, while we might be able to make progress without measurement, we do need proof to satisfy everyone else.
Geographic range expansions by plants and animals have presented a number of puzzles to scientists. The first of these is known as Reid’s paradox: species ranges often expand much faster than expected from normally observed dispersal rates.
