The browse line
The browse line is a distinctive line below which you don’t tend to see leaves or branches in places with ground animals, like deer, that enjoy eating leaves or branches.
Browse lines are basically caused by animals eating as high as they can reach. When everything below has been eaten, what's left behind can be a strikingly flat line of leaves at the base of the foliage.
Except for where there are giraffes or elephants where trees don’t stand much of a chance, even spiky ones.
This drawing is based on the beautiful Richmond Park in South West London which has a large number of old oaks and large herds of deer that leave a uniform underline to the canopy across the park.