Trying to understand the meaning of “clearing up”.
One of the meanings I see at Collins Dictionary is
When you clear up or clear a place up, you make things neat and put
Here’s some excerpt to give some context.
MOUSE - RUNNN! UNICORN - Hop onto my back! UNICORN - I see a clearing up ahead! MOUSE - That's not a clearing! It's the edge of a cliff!
In your context it is a clear place in a wood (a forest) — probably there were trees sometimes ago, but people chopped they down.