Since tree generation is not seed dependant, if I quit the game, and then go to the edge of the generated region, trees will be cut unnaturally along the border

Title explains most of it. Try exploring a jungle without quitting the game in a newly generated world. And then try again but quitting and reloading the world after spawning and waiting for some of it to generate, and then exploring. In the first case everything will be fine, but in the latter case you will see some artifacts.

P.S. This is not related to the failing to generate decorations on random quarter chunks bug.