Final answer:
The level of risk is determined by the likelihood and impact of a potential event, combining the probability of occurrence with the consequences of that event.
Step-by-step explanation:
The level of risk is determined by likelihood and impact. Risk in this context refers to the potential that a chosen action or activity (including the choice of inaction) will lead to a loss or an undesirable outcome. The concept of risk does not only involve species biology but also includes environmental damage, social and economic impacts, and public health issues, along with the feasibility of control or eradication.
Risk is defined as the product of the likelihood of an event occurring, and the severity of the consequences of that event (National Research Council, 2002). In other words, it's a combination of how probable something is to happen and what the consequences would be if it did happen. Risk analysis techniques, which are extremely important for preventing undesirable outcomes such as plant invasions, rely on a detailed understanding of both of these factors.