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.