We were also taught that weeds on native rangelands represent bad management. That is, they would not be a problem if only we did not blade the roadside, overgraze the range, or fail to control the weed problem on cropland. While these are true, it's only part of the truth and only the truth for some weeds. For example, native weeds move around mostly because disturbance has shifted the competitive balance. Easy movement, wide adaptation, intense domination and exponential growth characterize invasive weeds.
Most invasive weeds have seeds that travel far using special adaptations for hitching a ride.
Historical vectors include wind, water and animals. More recently, seed sacks, hay, machines, and vehicles have taken these seeds across the oceans and across the continent. Today, all of the above speed weed spread into new states, counties, watersheds, and from one ownership to the next. The more invasive weeds were already adapted to similar climatic conditions somewhere else in the world for a long time. Their wide adaptation helps them thrive.