Quote Originally Posted by Gumboot View Post
You're quite right, although trees don't grow where rivers are, as such. Rather both trees and rivers tend to end up in areas of high rainfall. Water in a river isn't much use to a tree, because trees don't grow in rivers. But rivers tend to flow where there's more rainfall. Trees get their water mostly from rainwater falling on the ground where they're standing. The water that isn't absorbed by trees ends up in rivers.

Generally speaking:

Higher rainfall = more trees + more rivers
Lower rainfall = less trees + less rivers
Actually on the great plains it is the rivers directly allowing the trees to grow, they aggregate the water, and bring in water from rainier areas, which allows the trees to grow in the river valleys despite not having any more rain than the surrounding plains.