History of Plant Invasiveness

Weed species, invasive or otherwise, have advanced lock-step with the rise of agriculture and the advancement of human cultures. In North America, the introduction of exotic species began with the first colonists and continued unabated with the rise in global trade. So what changed late in the 20^th century to explain the meteoric rise in the science of biological invasions? Have scientific advancements in ecology shown us a new path? Have urban sprawl and habitat fragmentation left a void to be filled by an opportunistic cultivated flora? Has there been a significant evolution in values that competes with objective science and politicizes invasive species, turning the very act of cultivating plants into a series of moral judgments? Plants originallycultivated for ornament are prime targets, as they are often viewed as having the least value but the highest risk in invasive risk cost-benefit scenarios.