Arborists are called tree surgeons because their function is comparable to that of a physician. However, the two terms might never get used concurrently in the industry.
A tree surgeon's job is to ensure the health of trees through pruning, fertilization, and other means. But it also includes planting fresh stock and removing trees to reclaim an area or simply because the tree itself is unhealthy, as well as pruning old trees that have overgrown to maintain their health.
There is an inherent risk in doing tree surgery for the people doing the procedure and everyone in the immediate area. Those in the trees and people on the ground are both vulnerable to injury from falling trees and branches.
Though formal education in the field is available, there are no prerequisites to becoming a tree surgeon. However, to work as an official arborist, you must earn either a National Certificate in Arboriculture or a more advanced qualification in the field.