The area by the creek is full of invasive species - primarily paper mulberry and ligustrum. Invasives cannot be cleared all at once both because it is a large amount of work, and because it would destabilize the ground. This will be continuous work, with larger portions completed by contractors and maintenance completed by volunteers.
Here is a fantastic guide on girdling for which we can take no credit!
PHASE: PLANNING FOR CONTRACTOR; VOLUNTEER WORK UNDERWAY