Here is a list of approximate tree lines from locations around the globe : Like the alpine tree lines shown above , polar tree lines are heavily influenced by local variables such as aspect of slope and degree of shelter .
Given this caveat , here is a list of average tree-lines from locations around the globe : Like the alpine tree-lines shown above , polar tree-lines are heavily influenced by local variables such as aspect of slope and degree of shelter ; trees can often grow in river valleys at latitudes where they could not grow on a more exposed site .