What it is
Nature is all the living things we see everyday, the trees, grass, birds, squirrels, and flies. It is the plants and animals and fungi and other living things in the world around you. All of these living things work together to help keep everything else alive. This wide array of living things is something scientists call biodiversity and it's critical to keeping everything from moss to humans alive.
These webs are very complex and very delicate
All the living things in this picture, those you can see and those you can not, rely on one another to stay alive.Credit: Wikimedia Commons
Every living thing in the picture to the right and outside your window and at the park down the street has a role to play in keeping everything else around it alive. Like so many other things on this website, the issue at hand really comes down to energy. The energy for nearly every living thing comes from the sun. This energy is then passed from living thing to living thing through a series of connections called the food web that involve one living thing eating another to harness it's energy. These webs are very complex and very delicate, with different living things having evolved for millions of years to get to be what they are right now. Disturbing this web by removing one part puts stress on all of the other parts. Think of it like building a block tower. If you build a huge structure with hundreds of blocks, removing only one or two can put significant additional stress on neighboring blocks, causing them to shift and put pressure on other blocks until something finally gives.
This link will focus on biodiversity as a general concept and then move on to talk about protecting the biodiversity of plants and animals, and general methods that help to maintain biodiversity including protecting and repairing natural spaces. While there are a number of other living things involved in this very complicated web, the ones that we seem to be doing the most harm to and that we can do the most to help out are plants and animals. The fact that we don't focus on other living things in most conservation efforts is more reason to try to protect and fix spaces in general.