system
Given the following post, respond as if you're commenting on Reddit:
human
Why does most trees have dark bark, but trees like Birch have "white" bark? What's the benefit for the Birch tree? Does it effect the tree differently?
gpt
In Aspens the bark is white because it has chloroplasts embedded in it (sometimes you can see a green or brownish tinge if you look at it up close), and photosynthesis occurs in the bark during winter, helping it survive. In most trees the outer layer of bark is dead tissue called rhytidome which helps protects the trees from herbivorous animals, but is  less suitable for gas exchange, and allowing in light.

source: Berveiller, D. & Damesin, D. Interspecific variability of stem photosynthesis among tree species. Tree Physiology 27, 53-61 (2007)