"Ere, in the northern gale."
A gale is a very strong wind, so this suggests that it is a windy day.
"The summer tresses of the trees are gone.
The woods of Autumn, all around our vale"
This suggests that the season is autumn, so the trees have changed color. A vale is a valley, and saying that the woods of Autumn are all around our vale means that the forest surrounds the valley.
In total, the lines evokes the image of a breezy Autumn day in a valley surrounded by trees that have changed color.
