The Entwood, also called Fangorn Forest (somewhat conjectural)

The dark canopy of Fangorn Forest covered much of Rohan's northern border, but the Men of that land were afraid of the trees, and stayed away from the mysterious wood. The Entwood was their name for it in their own tongue, but by the time of the War of the Ring, any meaning this name might have held was long forgotten. To the Rohirrim, the Ents of the Entwood were no more than fanciful tales, until those Ents were roused in anger against Saruman and helped to rescue the Riders of Rohan from his forces.