The Hoa River Valley on the Olympic Peninsula in the state of Washington is a prime example of old-growth temperate rainforest. In these pristine ecosystems, western hemlock (Tsuga heterophylla, Sang.) seedlings often establish on rotted fallen logs (left picture). Western hemlock can live to be 500 years old and have stem diameters of 0.5 - >1m. The picture on the right shows a series of old trees that established on a fallen log several hundred years earlier. Each species has a 'regeneration niche', a set of environmental conditions (microhabitats) that favor successful seedling establishment.