Gather the type of seed you would like to keep in your area and then go on a chopping spree. Cut EVERYTHING in your path to small logs (you can go back and either turn into firewood for logging xp or work on your woodcrafting with them). Eventually you will get your zone down to a managable limit. Our zone currently looks like Paul Bunyon went mad but we already have dozens of saplings appearing. We will either have everyone maxed skill or disappear behind walls of forestation.