This is poison ivy (Toxicodendron radicans). This is a plant that everyone should be able to identify. Around 85% of people are allergic to poison ivy, though sensitivity varies greatly. Poison ivy is native to the Southeast and is recognizable by its three leaflets and hairy-looking vines. Remember the saying, “Leaves of three, let it be.” The shape of the leaflets may confuse some, as they may have toothed margins, as seen above, or smooth margins. All parts of the plant contain urushiol, the oily compound responsible for allergic reactions. For more info and tips on identifying poison ivy, see HGIC 2307, Poison Ivy.
Those who are particularly observant may have noticed a second vine in the photo on the very left side of the tree. This is another native: crossvine (Bignonia capreolata).