Here is tree trunk (on the edge of a shopping center parking lot) covered with layer of poison ivy vines. 

Both the grey vines and the red, hairy vines are all poison ivy.

The grey branches that stick out don’t need the hairy roots to hold on to the tree, so they don’t have them.

The thick, red, hairy vines climb the tree and then sprout out the horizontal grey branches that go collect sunlight.

Poison ivy is a very smart and adaptable plant.