Mast is a term that refers to the fruit produced by trees and plants. Examples of mast are, acorns, hickory nuts, pine cones, sweet gum balls, berries, fruits, grass seeds and fungi. Many people do not like trees that drop their seeds or fruit because they perceive them as messy. Plants and animals on the other hand need them for survival. Mast provides food for animals, it produces the next generation of plants, and it also puts nutrients back into the soil as it decays.
Dead trees provide homes for cavity nesting birds.
Snags are home to many insects, birds, and mammals. By leaving snags you are providing these animals a natural home in which to live and raise their young. When you remove a snag the animals may look to your garage, shed, or your home for their next shelter. Fallen logs are an ecosystem in themselves. The decaying wood provides a growing medium for ferns, orchids, and mushrooms.