Well, like it or not, most forests have been impacted directly or indirectly by man since we became the dominant species on this planet. A prime example of this is fire.
Fire is a management tool that has been used and misused by man since prehistoric times.
Because of man's use of fire and other activities that have had an impact on our forests, they are not totally natural ecosystems anymore. Also, there are a number of products and services that we desire from and are dependent on our forests for. The most obvious of which are wood and paper products. We have a ravenous and growing appetite for lumber, plywood, paper, etc. The list of products is almost endless.