Answer:
By describing the poplar as lonely and restless, the poet creates the mood of being sad.
Explanation:
The mood of a poem is the sensation that the author wants the reading of the poem to convey to the reader. In "Poplars" written by Edward Bliss Reed, we can see that the author tries to create a mood of sadness and melancholy, by presenting a tree that is not appreciated, even if that tree longs to have contact with humans and make them happy.
This tree is the Poplar, where the author reiterates the idea that it is a lonely tree, but restless, because it tries to attract attention, being ignored at all times. This endless loneliness together with this desire to have company, transmit a mood of sadness, melancholy, abandonment and even loneliness.