Species form the ecological underpinning of forest ecosystems, and are critical for their long-term successful functioning. Urban forests are composed of both native and non-native organisms, but those that have adapted locally are considered to be better able to survive and grow under these conditions. Invasive species are often introduced into urban forests because they are thought to survive better with lower inputs of water, minerals, and pesticides, however, in these new environments they usually escape and cause major disruptions.