The answer to your question is: Antecedent
It's a thing or event that existed before logically precedes another
Example: Some Antecedents to the African novel might exist in Africa's oral traditions
Synonyms: Precursor, Forerunner, Predecessor.
"the guitar Antecedent"
The motto means that you should reduce the trash that is causing pollution. Also, that you should follow the idea of conservation and conserve any renewable resources by recycling them.