section_path: Ecology
section_name: Ecology
paragraph_text: Ecology
  
  Urban ecosystems, influenced as they are by the density of human buildings and activities, differ considerably from those of their rural surroundings. Anthropogenic buildings and waste, as well as cultivation in gardens, create physical and chemical environments which have no equivalents in the wilderness, in some cases enabling exceptional biodiversity. They provide homes not only for immigrant humans but also for immigrant plants, bringing about interactions between species that never previously encountered each other. They introduce frequent disturbances (construction, walking) to plant and animal habitats, creating opportunities for recolonization and thus favoring young ecosystems with r-selected species dominant. On the whole, urban ecosystems are less complex and productive than others, due to the diminished absolute amount of biological interactions.
  
  Typical urban fauna includes insects (especially ants), rodents (mice, rats), and birds, as well as cats and dogs (domesticated and feral). Large predators are scarce. However, in North America, large predators such as coyotes and other large animals like white-tailed deer persist.
  
  Cities generate considerable ecological footprints, locally and at longer distances, due to concentrated populations and technological activities. From one perspective, cities are not ecologically sustainable due to their resource needs. From another, proper management may be able to ameliorate a city's ill effects. Air pollution arises from various forms of combustion, including fireplaces, wood or coal-burning stoves, other heating systems, and internal combustion engines. Industrialized cities, and today third-world megacities, are notorious for veils of smog (industrial haze) that envelop them, posing a chronic threat to the health of their millions of inhabitants. Urban soil contains higher concentrations of heavy metals (especially lead, copper, and nickel) and has lower pH than soil in the comparable wilderness.
  
  Modern cities are known for creating their own microclimates, due to concrete, asphalt, and other artificial surfaces, which heat up in sunlight and channel rainwater into underground ducts. The temperature in New York City exceeds nearby rural temperatures by an average of 2–3 °C and at times 5–10 °C differences have been recorded. This effect varies nonlinearly with population changes (independently of the city's physical size). Aerial particulates increase rainfall by 5–10%. Thus, urban areas experience unique climates, with earlier flowering and later leaf dropping than in nearby countries.
  
  Poor and working-class people face disproportionate exposure to environmental risks (known as environmental racism when intersecting also with racial segregation). For example, within the urban microclimate, less-vegetated poor neighborhoods bear more of the heat (but have fewer means of coping with it).
  
  One of the main methods of improving the urban ecology is including in the cities more urban green spaces: parks, gardens, lawns, and trees. These areas improve the health and well-being of the human, animal, and plant populations of the cities. Well-maintained urban trees can provide many social, ecological, and physical benefits to the residents of the city.
  
  A study published in Scientific Reports in 2019 found that people who spent at least two hours per week in nature were 23 percent more likely to be satisfied with their life and were 59 percent more likely to be in good health than those who had zero exposure. The study used data from almost 20,000 people in the UK. Benefits increased for up to 300 minutes of exposure. The benefits are applied to men and women of all ages, as well as across different ethnicities, socioeconomic statuses, and even those with long-term illnesses and disabilities. People who did not get at least two hours – even if they surpassed an hour per week – did not get the benefits. The study is the latest addition to a compelling body of evidence for the health benefits of nature. Many doctors already give nature prescriptions to their patients. The study did not count time spent in a person's own yard or garden as time in nature, but the majority of nature visits in the study took place within two miles of home. "Even visiting local urban green spaces seems to be a good thing," Dr. White said in a press release. "Two hours a week is hopefully a realistic target for many people, especially given that it can be spread over an entire week to get the benefit."