All landscape features should be treated as significant and historic until research and planning efforts are undertaken to prove otherwise. This will ensure that potentially historic features are not removed or altered while planning is ongoing. For example, maintenance may involve the rejuvenation rather than removal of an old hedge or replacement in-kind of a tree that has become a safety concern.
During the research and planning process, maintenance operations should continue to focus on minimizing disturbance, and protecting and stabilizing deteriorated features.
After Treatment is implemented, maintain features to preserve the historic character: retain historic features in good condition; remove and replace features in-kind when they begin to adversely affect character or deteriorate beyond repair.
(Guide to Developing a Maintenance Plan for a Historic Landscape)