Minecraft wiki entry for Big_Dripleaf, associated text: Big dripleaves consist of any number of non-solid stem blocks atop of each other and a single leaf as the uppermost block, which can be stood on by any entity like a normal block for 1 second (20 game ticks). After this time, it tilts down, becoming lower than a block and giving a player warning that it is about to collapse. After a few ticks, it tilts down and becomes temporarily non-solid. When the leaf is powered by redstone, it does not tilt or collapse, however. Powering the stem has no effect.