Paul Carter (right), a horticulturalist with the Norfolk District of the US Army Corps of Engineers, and Stephen Van Hoven, chief of the Horticulture Division at Arlington National Cemetery, measure the circumference of the trunk of a fallen tree in the Millennium Project site at Arlington National Cemtery in Arlington County, Virginia, in the United States on February 6, 2013. The red oak tree was felled as part of the Millennium Project, which will clear 27 acres of property on the cemtery grounds. The project will add an additional 30,000 burial and inurnment sites. Horticultural experts estimated the age of a number of trees in the Millennium Project site based on height, trunk circumference, and other factors. Many of the oldest, non-invasive trees will be retained. Experts use the data collected from initial trees felled as part of the project to confirm these estimates of age.