When tree bark becomes damaged, it opens a tree up to insects, disease and fungus. Even a 100-foot tall, century old tree may perish from a small area of damage. This is especially important during pruning and trimming work -- tree professionals must be careful to avoid damaging the tree they are working on. This is why professional tree workers do not use spikes to climb live trees, and are careful to lower cut branches in a manner that prevents them from hitting and damaging the tree (or parts of your property!).