capable of doing significant harm to ecosystems, economy or public health;
capable of spreading without apparent natural controls (natural predators, disease);
population levels that are unchecked;
causing major change faster than native ecosystems can accommodate;
changing major ecological processes (nutrient cycling, hydrology, fire regime, energy);
destabilizing environmental (physical or community) structure;
forming undesirable monotypic stands of vegetation that replace diverse communities;
reducing biodiversity/integrity, causing extirpations and extinctions;
reducing or eliminating a natural product, ecological service or other valued attribute.