What causes tree lines?

Question

There is an area of where there is a distinct line of only trees on one side and only shrubs on the other (right next to each other). What could cause this? My attempt: I said there could be a difference in sunlight, but I'm not sure.

Answer 1

Differences in sunlight can surely cause a tree line. There are multiple types of tree lines and such examples include differences in rainfall, elevation, and soil. There are some great example pictures of tree lines caused by elevation if you do a quick search.

It could also be due to humans. Perhaps someone is preventing the shrubs from moving towards the trees and vice versa.

It all depends on the environment.