Girdling is a slow process and more useful on large trees you don’t want to fall on younger trees that you want. A large maple may take years to die and maybe 10 years to be mostly on the ground. Keep in mind girdling causes a dangerous area even for one tree as it dies. I would just drop any smaller trees and then spray the stumps. Or hack and squirt the small stuff. Girdling an entire area is going to create a no people zone for quite a while.