Old-growth forests are known for having a forest floor that dips and rises, a characteristic called pit and mound topography. When a large tree falls, part of the roots and attached soil may be lifted out of the ground, leaving behind a pit where the roots were. As the uplifted roots decay, they form a mound next to the pit. Although trees fall and decay in all forests, it can take centuries for pit and mound topography to form across a large area, making it a common feature of old-growth forest