When you look at the tree line and it just looks like a wall of vegetation the undergrowth has become too thick, this stops airflow from penetrating to the forest floor and slows the growth of the trees. This will cause the air to be very humid and hot which accelerates the growth of fungus and causes tree rot. By removing the undergrowth and allowing air flow, the woods will be cooler and healthier, this will also help the wildlife. Under growth and be harmful to even larger trees. Vines like poison ivy and kudzu can even grow to be so heavy that it will break trees then choke out the sunlight making them die off. This can be extremely dangerous as the tree will slowly decay till the day comes and it finally comes crashing down damaging anything it hits. A forestry mulcher can remove the undergrowth before it has the chance to damage any trees or remove the affected trees and stop the spreading.
