Final answer:
The correct tag for the sentence is "don't they?", following the rule of changing a positive statement to a negative tag by using the auxiliary verb "do" and the subject pronoun "they".
Step-by-step explanation:
The correct tag question for the sentence "Woodcutters fell the trees for smuggling," would be "don't they?". The structure of tag questions in English involves repeating the auxiliary verb from the main sentence and changing it to negative if the main sentence is positive (and vice versa), and then adding the subject pronoun.
Since the main sentence is in the present simple tense and is a positive statement, the auxiliary verb "do" is used, turned into its negative form "don't", and followed by the pronoun "they", referring to the woodcutters.