An urban ecosystem is any natural system located within a city or other densely settled area. Urban ecosystems are an interface between biological communities of plants and animals and urban infrastructure. They can include urban forests, native plantings, or green infrastructure such as green roofs, community gardens, and rain gardens. These ecosystems provide an array of services for cities and their residents, including reducing energy consumption, improving air and water quality, and lowering ambient temperatures. While these systems can aid in mitigating the effects of climate change, they are also threatened by the extreme events brought on by climate change.
Urban vegetation is at risk of exposure to increased stormwater runoff and pollutants because of climate change. These impacts could reduce the ecosystem’s ability to improve water quality and regulate the flow of water. Rain gardens, depending on their design, may be less effective at mitigating flooding from extreme precipitation events, which could result in an increase in pollutant loads and increased stormwater runoff. Severe flooding and high salinity could also kill many plants within an urban ecosystem.
Increased carbon dioxide levels and higher temperatures could lead to increased tree growth. The increased growth promotes carbon dioxide uptake, but that uptake may be offset because extreme heat can cause stress in trees. Heat waves can damage a tree’s ability to uptake carbon dioxide or ultimately kill the tree, leading to further increases in atmospheric carbon dioxide. Extended periods of drought will also result in less carbon dioxide uptake since trees halt gas exchange to protect water storage functions.
Changes in climatic conditions can also result in shifting geographic ranges for many species. For example, maple species are often popular trees to plant in urban ecosystems. However, warming temperatures are likely to result in dwindling numbers of maple trees in cities across the United States due to their preferred temperature range and drought intolerance. Since urban trees decrease ambient air temperatures, a decrease in trees could also lead to greater impacts from extreme heat on urban areas.
Wildlife depends on vegetation to continue living in cities. Urban trees provide shelter and forage to animals like squirrels, chipmunks, and birds, while prairie plantings and shrubs provide cover for rabbits and food for pollinators. Without a consistent source of shelter and food, these animals are not likely to survive, or they will be forced to relocate.