Not usually. Cats often climb trees to avoid perceived dangers that they encounter at the bottom of the tree. Given plenty of time for them to calm down, most cats climb down on their own without incident. You can speed the process up by leaving a can of their favorite food on the ground near the tree. Suprisingly, cats aren't as happy to be "rescued" as their owners and a cat with claws actually pose a danger to a firefighter who attempts to pluck it from its perch before the cat is ready.