Answer:
The dark moths were better hidden from predators and therefore more of them survived and this allowed them to have offspring.
Step-by-step explanation:
If all of the light colored trees disappeared and there are only dark colored ones, then that means that the light colored moths wouldn't be able to live long since their traits wouldn't match the environment. This then leads to the conclusion that dark moths would be better hidden since their trait fits their current environment and would let them be hid much better from predators. This would allow them to survive longer and eventually, reproduce.