Ann Arbor's "Tree Town" nickname stems from the dense forestation of its parks and residential areas. The city contains more than 50,000 trees along its streets and an equal number in parks. In recent years, the emerald ash borer has destroyed many of the city's approximately 10,500 ash trees. The city contains 157 municipal parks ranging from small neighborhood green spots to large recreation areas. Several large city parks and a university park border sections of the Huron River. Fuller Recreation Area, near the University Hospital complex, contains sports fields, pedestrian and bike paths, and swimming pools. The Nichols Arboretum, owned by the University of Michigan, is a 123-acre (50 ha) arboretum that contains hundreds of plant and tree species. It is on the city's east side, near the university's Central Campus. Located across the Huron River just beyond the university's North Campus is the university's Matthaei Botanical Gardens, which contains 300 acres of gardens and a large tropical conservatory.

What is the city of Ann arbor nicknamed as?