Thanks for the feedback, the patterns are just a first pass on the design. Green forests are like ours, photosynthesisers. Black forests are indigenous flora which do something I call anemosynthesis. They generate chemical energy not by absorbing light but by mechanical means. They developed in the perpetually dark part of the planet to utilise the strong, constant winds as an energy source. Instead of leafs they have flappy sort of membranes or wings which are moved by the wind and in that way generate chemical energy which is used to make oxygen and simple sugars. Their trunks are dark brown or black, that's why theyre called black forests. Now these planets are most often present on the colder, more nocturnally facing terrains. Mixed forests exist as well, of course.