An invasive species is an organism that causes ecological or economic harm in a new environment where it is not native

The urban heat island effect appears in towns and cities as a result of human activity. The heat generated by people, transport, shops and industry is trapped in the narrow roads and concrete structures, unable to escape to the atmosphere. This can bring the temperature in urban areas up 3-4°C higher than the surrounding countryside, and with that comes a vicious cycle.

Researchers estimate that nine million people die every year as a direct result of air pollution. In London, two million people - of which 400,000 are children - are living in areas with toxic air.

As our cities grow and more people move into already crowded spaces, what do we need to do to transform our urban areas into healthy places to live? An increasing body of research tells us that we should be letting nature back in.