They may just be trees or stumps but for me there is as much learning in them as in the study of a leg or arm. Beautiful form, structure, flow and rhythm.
Years ago I would take my Sheridan Animation students to draw a beautifully gnarled rotting beech trunk. It had as much expressive gesture as the best model.
These studies were done with my Humber Animation students at the nearby Arboretum. Same lesson to be learned by all of us.