All animals are dependant on plant life, whether they are meat eaters or not. Trees provide shelter and food. Some animals that are vegetarian are food for larger as well, trees provide oxigen. Where there is no plant life, there is very little life.
That depends on what animal your thinking of,a leaf eating tree dweller would be very dependant on tree's ,such as a sleuth or cowarla bear.
Because trees give air that people and animals breath in, and food for animals even humans and caterpillars and ladybug can only survive on one plant an shelter, there is so many reasons
They depend on trees for on it for food and shelter DUH !