also occurred in the Lake. However, concerts in the Ramble were a short-lived phenomenon. A concert pavilion in the Mall, at the top of Bethesda Terrace, was approved in 1862, and by the pavilion's completion three years later, most of the concerts had shifted to the Mall. Decline The maintenance effort of the Ramble and Lake, as did the rest of the park, declined slightly in the early and mid-20th century. In 1927, mayor Jimmy Walker commissioned Herman W. Merkel, a landscape designer, to survey the park and create a plan for improvement. Merkel's report noted that while the condition of the Ramble was "disreputable" with its many dead plants and trees, Central Park's overall condition was "fairly good". Some structures were closed or demolished in the mid-20th century. The Cave was closed by 1934 due to crime. The deteriorating boathouse on the Lake was closed in 1950 and replaced in 1954. By 1971, the Ladies' Pavilion had also been destroyed by vandals, though it was replaced two years later. Restoration The Ramble was partially restored in the late 20th century. These renovations started with the Ladies' Pavilion, which was restored to its original design in 1979. In early 1981, the Central Park Conservancy cleared trees in the Ramble to allow more sunlight to reach the Ramble. However, this decision was criticized by birders, who said that the destruction of trees would remove shelter places for birds. The restoration of the Gill was subsequently approved in 1982. A path in the Ramble, Iphigene's Walk, was dedicated in 1987 to one of the key backers of the Ramble's 1980s renovation. The Central Park Conservancy renovated the Lake's shoreline starting in 2006, in a project to enhance both its ecological and scenic aspects. In mid-2007, the first phase of a restoration of the Lake and its shoreline plantings commenced, with replanting using native shrubs and understory trees around the northern end of the Lake. In the earliest stages, invasive non-native plants like Japanese knotweed were eradicated, the slopes were regraded with added humus and protected with landscaping burlap to stabilize the slopes while root systems became established and leaf litter developed. Bank Rock Bridge was recreated in its original materials following Calvert Vaux's original design of 1859–60. The replacement bridge was made of steel, clad in ornamental cast iron facings, with a wooden deck. The new bridge was rededicated in September 2009.