The whitebark pine tree grows in high-elevation ecosystems in the northwestern area of the United States. Its population has been limited due to the human introduction of a fungal disease, known as white pine blister rust, to western North America in the early 1900s. In some populations of whitebark pine, there is relatively little natural resistance to white pine blister rust. Based on this information, what would be the best long-term solution to mitigate the adverse impacts of the fungal disease on whitebark pine trees?