This mural is a reference to The Lorax by Dr. Seuss (one of which is sometimes watched in APES). The colorful tree is a Truffula tree (which are the raw material used to make thneads, a multipurpose cloth that everyone needs). The brown animals are Brown Bar-ba-loots. The Onceler (who cut down the trees) tells anyone who comes by about what once was and what needs to happen through the slats in his window. His advice also applies to the world because it can inspire people to change their lifestyle and work to stop humans' degradation of the environment.