Olympic

The Olympic Mountains form the centerpiece of Olympic National Park. Unlike Mount Rainier and other volcanic peaks in the Cascade Mountains, the Olympic peaks are not volcanoes. Instead, the Olympic Mountains and the Coast Range along the Oregon Coast were created when the surface of the sea floor folded up against the leading edge of the continent as the heavier oceanic plate was deflected under the lighter continental plate. In this area, the oceanic plates are sliding under the North American Plate. Thus, the process of plate movement is responsible for the creation of 2 types of mountain ranges in the Northwest (information from summary by Schultz, 1990:11-16).

The summit of the highest peak in the Olympic Mountains, Mount Olympus (2,428 m = 7,965 feet), receives 500 cm (200 inches) of precipitation per year, mostly as snow. Although only half the height of Mount Rainier, the northerly latitude of the Olympic Peninsula means that the mountains are still high enough to support glaciers (photograph above) and develop subalpine meadows, such as seen on Hurricane Ridge (photograph below). Summits in the Coast Range are not high enough to support glaciers or alpine zones. Olympic marmots (Marmota olympus) sometimes can be seen in the grassy meadows of the Olympic Mountains. They are one of several endemic species and subspecies that evolved as distinct taxa on the Olympic Peninsula while they were isolated by glaciers that once filled Puget Sound and covered the Cascades.

Because the Olympic Mountains and Coast Range virtually rise from the sea, they cause the moisture-laden Pacific air to rise and cool, lowering its capacity to hold water. Thus, most of the precipitation falls along the western slopes of the mountains. The same is true of the other mountain ranges that we visit. In the Olympic Mountains, the lush temperate rain forests in the river valleys of the western portion of the park, such as the Hoh River Valley (photographs below), receive 356-424 cm of precipitation each year (about 12-14 feet). On the eastern side of the mountains, the now drier air warms as it flows down to lower elevations, decreasing its relative humidity. This results in less precipitation on this side of the mountain range. Thus, the town of Sequim (pronounced "skwim"), located in the rain shadow on the northeastern part of the Olympic Peninsula, receives an average of only 43 cm (17 inches) of precipitation per year.

The temperate rain forest of the Pacific Northwest coast includes many of the same species of trees found inland in the Cascades, but the rain forest is dominated by western hemlock (Tsuga heterophylla) and Sitka spruce (Picea sitchensis), the latter referred to as an "indicator species" of the rain forest. Only one species of pine is native to the lowland coastal forests of Washington and Oregon. The shore pine (Pinus contorta) is actually the same species as the lodgepole pine in the Rocky Mountains and Great Basin. Mosses, club-mosses, lichens, and ferns are also abundant.

Because of the competition for resources on the floor of the rain forest, seeds from Sitka spruce and other plants establish themselves on fallen trees, called nurse logs. These logs can cover 10-20% of the ground in the Olympic and Cascade mountains (summary by Schultz, 1990:269). The nurse log eventually decomposes, but the young trees mark its former location as they grow in a line referred to as a colonnade (first photograph below). The tops of stumps also serve as a site where plants can establish themselves. In the second photograph below, the 2 trees straddle a nurse log, but the tree in the foreground has died, and its stump now has plants growing on it.

Most of the biomass in the rain forest is contained within the trees, and the nutrients are largely unavailable to the various consumers in the food web. Consequently, much of the food web in the rain forest is supported through decomposition of the fallen leaves and branches, as well as the fallen trees that serve as nurse logs. These logs serve as a home and nutrient source for a wide variety of organisms. Initially, wood boring arthropods (beetles, ants, termites, and mites) tunnel into the wood to feed or nest. Into these tunnels come the fungi and bacteria that will help to break down the wood. Leaves and other forest litter, as well as mosses, accumulate on top of the log and provide a place for seeds to germinate. This new growth on the log and the chunks of woody material that fall from the crumbling tree create additional habitat for a variety of animals, including nematodes, insects, spiders, slugs, snails, salamanders, and small mammals. Many of these animals feed on the nutrient-rich fungi, which are easier to digest than the plant material. Standing snags are important in many of the same ways, but they also serve as vital nesting, perching, and feeding sites for several species of birds and mammals (summary by Schultz, 1990:268-279). Although the rain forest is noted for its abundance of life, it is the dead material that supports much of the forest's interesting biota and ecological processes.

The temperate rain forest along the Pacific Coast extends from Alaska to northern California. We have several more nights to camp in this ecosystem along the Oregon and California coasts.