19 A further argument for the avenue’s importance was Massachusetts Avenue Architecture: Volume 2, which the CFA published in 1975, documenting more of the avenue’s buildings and early landscape 36 The problem was—and remains— that these federal and local preservation rules apply to buildings and other structures but not landscape The DC Historic Preservation Review Board, for example, reviews building alterations and other construction, including paving and retaining walls, but it has no jurisdiction over the associated landscape 37 So Mass Ave building owners were constrained by historic designation and the mansions individually were saved But owners were—are—mostly free to cut down trees, widen or make new driveways and turn the green “parking” into car parks Shocking loss, roots of recovery How far Washington had come from being a “city of trees” would be documented By the 1990s, urban forest policy was being revolutionized by mapping and imaging tools An American Forests study in 1999 showed that Washington had lost 60 percent of its major tree canopy between 1973 and 1997 38 Scientists also measured the rising “heat island” effect over Washington and associated damage to public health The American Forests study of Washington sparked these developments: • Philanthropist Betty Brown Casey endowed a nonprofit organization, Casey Trees, “to restore, enhance and protect the tree canopy of the nation’s capital ” Since starting in 2002, it has planted more than 17,300 trees and added immeasurably to the capital’s expertise in urban forestry39 • The city passed a law that restrains cutting trees on public or private land 40 The DC tree law bars cutting “special” trees of 55-inch circumference or greater Someone seeking to remove such a tree Fig. 31 The shocking loss of tree canopy over Washington was measured by an American Forests study released in August 1999. At far left, the canopied area in 1973 is green. Below, the green canopied area has shrunk dramatically by 1997. Landsat MSS 1973 80 Meter Pixel Resolution Landsat TM 1993 30 Meter Pixel Resolution
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