Competition to fill the canopy is apt to be fierce, and younger trees of different species may compete to fill the canopy. This multi-layered canopy efficiently traps moisture from fog so that even during the dry season the massive trunk of an ancient redwood may contain thousands of gallons of water. This reserve of moisture and a thick, protective bark enable redwoods to survive wildfires. In the Pacific Northwest, old-growth forests are ecosystems dominated by large conifers of an age predating European influence. The dominant trees in coastal redwood forests range from several hundred years to over two thousand years.
Snags are another characteristic feature of an old-growth forest.
These large, erect, dead trees may remain standing for decades, or even centuries. Large, down trees may lie on the forest floor, gradually decaying, for many hundreds of years. Only in old-growth forests are young, old, dead and down trees all present at the same time. These forests are truly ancient. Their appearance has changed very little over time.