An old-growth forest (also termed primary forest, virgin forest, primeval forest, late seral forest, or in Britain, ancient woodland) is a forest that has attained great age without significant disturbance, and thereby exhibits unique ecological features and in some cases may be classified as a climax community. Old-growth features include diversity of tree-related structures that serve as diversified wildlife habitat that leads to higher bio-diversity of the forested ecosystem. Diversified tree structure includes multi-layered canopies and canopy gaps, high variance of tree heights and diameters, diversity of decaying classes and sizes of woody debris, and diversity of tree species.