Usually old-growth forests have multi-layered, open canopies. The interwoven canopy often blocks sunlight from reaching lower trees or the forest floor. The old forests also include varied tree heights and diameters, with large fallen logs (or tree trunks) across the forest floor. In Europe, less than 7% of forests are old-growth, as mainly due to industrial logging in the 20th century. In the United States, estimates are that only 10% of old-growth forests remain. In Asia old-growth forests are sometimes lost in regional conflicts.