How do the personified trees and brook re-establish a mood of gloom

There is a sense of darkness about the forest that casts a pall on Pearl, Hester, and Dimmesdale. Chapter 19 is filled with shadows in the forest being exposed by intermittent light. This represents the lives of these individuals who live within shadows of the village. Villagers only periodically see the light that shines in them.

This image, so nearly identical with the living Pearl, seemed to communicate somewhat of its own shadowy and intangible quality to the child herself. It was strange, the way in which Pearl stood, looking so steadfastly at them through the dim medium of the forest-gloom; herself, meanwhile, all glorified with a ray of sunshine, that was attracted thitherward as by a certain sympathy. ch 19