Warning. This is a trick question. That lovely shade of gold in the distance looks like a tree. But a closer look reveals leaves of three. And why does it look like the trunk continues up past the gold, to a part of the tree that's lost all its leaves?
Turns out this bright contribution to fall's glory is a poison ivy "tree"--a vine that has climbed halfway up a tree, then sent out branches to flower and set seed on. One thing to take note of in the forest is that vines never bloom when they're crawling on the ground. Only upon making an ascent, up a tree trunk or up and over a shrub, do they send out flower shoots.
There's something else telling about Princeton woods in this photo. The tree canopy at the top of the photo has lost nearly all of its leaves, while the understory is still green. One distinguishing feature of many exotics is that they hold their leaves later in the fall and green up earlier in the spring. As evidenced here, the trees are mostly native, while the understory is predominantly exotic. This difference in timing may have to do with the different climate in which the exotics evolved.