Plant pests and pathogens present a significant risk to global plant health and this threat is ever rising due in large to the growing global trade of plant material and, increasingly, evidence suggests that climate change is influencing pest establishment in new locations. Countries are using a number of phytosanitary measures in order to try and reduce this risk, including the use of Pest Risk Analysis (PRA) which assesses the potential impact a species could have on plant health were it to be introduced into a new region; thus identifying quarantine organisms.

A prominent issue in identifying and assessing plant health risks is that the most serious invasive alien species are often not pests in their region of origin. A prime example of this is the emerald ash borer which is not considered an important pest in its native range, however when introduced in the U.S. decimated ash tree populations there. For this reason the majority of the most damaging alien forest pests and diseases that have or have had a dramatic impact on temperate forests would not have been predicted as pests by conventional methods for assessing plant health risks.

Sentinel plants within botanic gardens and arboreta can play a vital role in providing information on future and/or known threats.