As I read your post, I was reminded of the Circle of Life Native American ideas dealing with the connection between people, animals, and nature. Everything has a purpose and we we disturb the purpose (erosion, over-development, extinction of species, etc.) it no longer works perfectly. You might consider that idea before you begin...maybe it will help you think of what you want your main theme to address.
You might want to start by choosing a single word that relates to the environment in some way, that also has many possible rhymes (assuming you want a rhyming poem, that is.) You could choose "sun", or "life", for example. Think of words that rhyme with your word of choice, and figure out how to connect phrases containing those words in the form of poems. You no doubt have had a poetry unit at some time in your schooling that gives the structures for various types of simple poems. If not, try the link below.
First you should decide that how you will relate and from which word.
You could also do a Diamante poem which allows you to use nouns, verbs, and adjectives to describe your topic. It ends up looking like a diamond. Check out this website and it will help you with your poem by walking you through step by step what should be written on each line.
You can include all different aspects of what make up the environment or what you think of the environment.
Another way to approach this is to write the word environment down the side of the paper and then write relevant words starting with each letter
Build your poem that way.
You should decide on what you want to say about the environment. Is it positive or negative? Do you want to talk about different causes, benefits, etc. Think of some nouns and verbs that relate to the environment.
Make something like an idea tree or cloud diagram with clusters of nouns, verbs adjectives, and see if you can rhyme words or not. Then decide how long you want the poem to be. Will it be a sonnet or anything longer? Think about it without any stress and you should be able to come up with a few ideas.
Well it's not suppose to be on one specific thing or I wouldn't be asking...It's suppose to be about the environment as a whole not one specific thing.