From the Super Mario Wiki, the Mario encyclopedia
Whispering Trees are a type of tree found in Paper Mario: The Origami King. They are found only in Whispering Woods. Many trees appear in the background and whispering about Mario and his actions, while Mario can directly talk to a few around Whispering Woods. At the Toad's BBQ Foodeatery area, a log cabin made of Ol' Grandsappy's wood and three logs (which want to be burnt) in a campfire are sentient and speak to Mario. Ol' Grandsappy and the Sap Sisters are members of these trees encountered deeper into the forest.