hope-for-the-planet:

Miyawaki forests (invented by Japanese botanist Akira Miyawaki) are tiny forests that can be squeezed into small open spaces (medians, backyards, schoolyards, etc) in otherwise developed areas. 

The technique of planting saplings of many different native species (ideally 30 or more) very closely together allows Miyawaki forests to grow 10x faster, be 30x denser, and 100x more biodiverse than conventionally planted forests.

In addition to storing more carbon than monoculture forests, these forests can also provide habitat corridors and food for wildlife. When planted alongside roads they can help reduce noise and filter pollution.

One of the great benefits of these forests is that any community with access to a small patch of open land can get involved and reap direct benefits from their work.