Yellow seems to be a very popular color among trees in the forest. One can't jump to conclusions when seeing a tree full of yellow flowers, or a single flower on the ground. This one I happen to know. The name of the tree is envira periquiteira (Cochlospermum sp.). I hope I got the genus name right. Notice the trunk of the envira. Those round holes are made by silvery marmoset monkeys, which consume the sap and resin of the tree.