It's trendy dumping uranium in the forest (6)
I believe the answer is:
poplar
'forest' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for poplar that I've seen before include "The tree that quivers" , "Tree of north temperate regions, with flowers borne in catkins" , "The tree is almost liked" , "Tall fast-growing tree; East London area" , "Timber tree" .)