The forest, dubbed “El Bosque Metropolitano” (the Metropolitan Forest), will be the new green lung of Madrid with over 450,000 new trees and other vegetation. It's part of a plan known as Madrid 360º, a series of measures being introduced by the city's government to improve air quality within the capital and meet the emission limits imposed by the European Commission. 
The forest will stretch along a 75km environmental belt around Madrid's perimeters with new parks, children's zones, dog trails and hiking and biking routes for city-dwellers and tourists. The first trees will be planted in October and will include native species such as wild olive trees, strawberry trees, willow, ash, elm, as well as gorse, rosemary, thyme and juniper and other bushes and shrubs.