While old trees can be found in a few other parks in Seattle, Seward Park’s Magnificent Forest, covering about 120 acres on the northern two-thirds of the Bailey Peninsula, is the largest stand of old trees in the city. Pacific Northwest old growth forest is characterized by trees of various ages including large trees over 250 years old, by a multi-layered canopy, by standing snags and by large down logs. The Magnificent Forest has these features, but for an old growth forest it is young, the majority of its trees being younger than 200 years.
The dominant tree of the Magnificent Forest is Douglas fir. Western red cedar, bigleaf maple and madrona are also well-represented. Western hemlock is found mainly toward the northern end of the peninsula. The shrub understory is composed largely of salmonberry, thimbleberry, elderberry, Indian plum, hazelnut, sword fern, and Cascade Oregon grape. The abundance of madronas, both in the forest and in the developed southern part of the park, indicates a well-drained, relatively dry site. The Bailey Peninsula is one of the few sites in Seattle where bedrock reaches the surface. The shallow soils overlaying the bedrock combined with the topography of the peninsula contribute to good drainage and dryness.
15,000 years ago the Puget Sound region was covered by the Vashon glaciation. After the ice receded 13,650 years ago, herbaceous plants first became established on the barren glacial debris, and it took about 1,000 years before trees (Douglas firs) became established.
Douglas fir can become established in open sunny locations, but does not grow well in shade, so shade-loving hemlocks and cedars theoretically succeed Douglas fir forests. Drier habitats, however, do not support hemlock and cedar well. In such locations, Douglas fir succeeds itself, depending on natural tree death, storms and wildfire to create openings where seedlings can become established. Tree ring dating on trees cut early this century indicated that the Magnificent Forest was severely burned in the 1490s. The relatively young age of many trees and the presence of burn scars on older trees suggest that it also burned in the early 1800s.
Conifers and many other trees form associations with mushrooms and other fungi in the soil. Tree roots become coated with fungal mycelium, inhibiting the growth of the root hairs that absorb water and nutrients. This does not harm the trees, but rather the fungal coating increases the efficiency with which they can absorb nutrients. The fungi in turn receive sugars from the trees. This mutually beneficial relationship is known as a mycorrhizal association. Different mushrooms and trees vary in the specificity of their choices for mycorrhizal partners. The same tree may have different associated fungi at different stages of its life. Fungal mycelium may connect adjoining trees in a nutrient web.
In addition to their crucial role in forming mycorrhizal associations, fungi perform another indispensable task in forest ecology. The decay of dead wood is carried out mainly by fleshy fungi. While woodpeckers, bark beetles and carpenter ants all contribute to the breakdown of wood, the actual decay is done almost exclusively by wood-inhabiting mushrooms, especially the polypores. These mushrooms have pores rather than gills and their fruiting bodies are often persistent on dead wood, adding a new layer of pores each year. Although decay is slow in northwest forests, the role of these fungi in returning the nutrients locked up in dead wood to the forest ecosystem is a vital one.
The Magnificent Forest is too small and isolated to support many of the animals, plants and fungi that characterize larger old growth forests, but it does provide shelter to mountain beavers, raccoons, Douglas squirrels, deer mice, western screech owls, bald eagles, pileated woodpeckers, and dozens of other bird species. Insects, spiders, and other invertebrates abound. The forest was home to mink until they were trapped in 1941, and to deer until 1952. The forest shores are visited by muskrats, beavers, river otters, red-eared turtles, and many kinds of fish and waterfowl.