A spring pole occurs when a sapling is bent over by another tree, creating high tension in the bend of the tree.  When a spring pole is "released" it can whip upwards, diagonal, or sideways creating an extremely dangerous situation for the forester.

Also called "widow maker", hangers are loose branches hanging from the top of a standing tree.  Falling limbs can get hung up in the crowns of neighboring trees and can fall onto foresters who are working below.  Hangers are also created when a forester or logger drops a tree that contacts a neighboring tree on the way down, breaking limbs which may hang for minutes or months.

Barber chairs occur when the tree splits in the middle when being cut.  One side of the tree violently splits into the air and can break loose when it reaches its pinnacle.  It then comes to the ground endangering the forester. 

This is an example of a bent tree under tension, however the trees are much larger than the sapling spring pole. These large trees are typically bent over when another tree falls on top of them, or, as in this case, a wind storm blows them over.  These trees are dangerous to cut as well, because like the spring pole, the forester does not know which way the tree will go when it is released.