Mount Rainier

With its summit reaching 4,392 m (14,411 feet), Mount Rainier is the tallest volcano in the 48 contiguous United States, and its slopes are covered with more glaciers than any other single peak in the country outside of Alaska. The processes of fire and ice (volcanism and glaciation) have built and eroded the peak over the past half million years or so.

The volcanic activity that created the Cascades (and earlier produced active volcanoes in the Sierra Nevada of California) results from the subduction of an oceanic plate beneath the lighter continental plate as they move in generally opposite directions. The heavier oceanic plate is deflected below the land on the continental plate. The materials comprising the oceanic plate melt when they descend to about 110 km below the surface. Because the oceanic plate is deflected under the land at an angle, it has moved several kilometers inland before the molten material rises to the surface and creates a chain of volcanoes, such as Mount Rainier and other peaks in the Cascade Mountains (summaries by Schultz, 1990:11-16, and Whitney, 1979:40-48). The volcanic activity associated with Mount Rainier is observable in the thermal vents at Longmire (brownish pools in meadow in photograph below).

Although the forests of the Northwest receive substantial amounts of rain and snow (photograph below), a summer "drought" favors the dominance of conifers over angiosperms. Coniferous trees have several physiological advantages. The evergreen needles on conifers permit photosynthesis for longer portions of the year, and they do not have to be replaced annually, which helps the tree to conserve nutrients. [Several broad-leaved understory shrubs in the family Ericaceae, such as salal (Gaultheria shallon), evergreen huckleberry (Vaccinium ovatum), and species of manzanita (Arctostaphylos), also have leathery, evergreen leaves.] The large surface area of the needles on conifers helps to keep the trees cooler during the summer, decreasing respiration and nutrient demand. Conifers also are generally better at storing water in their sapwood than most angiosperms (summary by Schultz, 1990:254-256).

On our hikes through the forests, students often notice the twisted trunks of snags that have lost their bark, which usually hides this growth pattern. The spiral growth improves the flexibility of the trunk, and this helps the tree to withstand strong winds and the weight of heavy snows.

Nitrogen typically is the limiting nutrient in northwestern forests. Some species of bacteria can "fix" atmospheric nitrogen (N2), incorporating it into molecules of ammonia (NH3), which can become available to plants as ammonium (NH4⁺). The success of red alder (Alnus rubra) in northwestern forests is partly due to the advantage imparted by the nitrogen-fixing bacteria growing in nodules on its roots. As with bacteria, some cyanobacteria fix nitrogen that benefits a partner. Although most lichens consist of a fungus and either a green alga or a cyanobacterium, some lichens, such as Lobaria oregana and L. pulmonaria (photograph below), are tripartite symbiotic relationships among a fungus, a green alga, and a cyanobacterium. The nitrogen supply of these and other "cyanolichens" becomes available within the ecosystem after they fall from the tree and decompose in the soil or they are eaten by animals, and it represents a substantial input of nitrogen into some ecosystems (summary by Schultz, 1990:264-265; Antoine, 2004).

Another typically unseen but nonetheless important group of organisms that benefit forest plants and influence community composition are the mycorrhizal fungi. Mycorrhizal fungi interact with the roots of vascular plants and receive carbohydrates and other products from their photosynthetic hosts. In return, they benefit the plants by 1) increasing the absorption of water and nutrients, 2) producing antibiotics that protect the fungus and host plant from bacterial infections, and 3) producing growth regulators that stimulate root growth. These fungi are also associated with nitrogen-fixing bacteria. Animals, such as rodents, feed on fungal fruiting bodies and spread the spores (summary by Schultz, 1990:262-263). Although the trees and other macrophytes are the most noticeable components of northwestern forests, their success or failure in the ecosystem depends, in large part, on the unseen organisms that help to drive the critical ecological processes, such as nitrogen fixation. For more on the nutrient ecology of plants, check this course webpage: Plants and Nutrients.

We spend part of our time in the park at Paradise (about 1,700 m = about 5,600 feet). Here, the high-elevation forest of subalpine fir (Abies lasiocarpa), Engelmann spruce (Picea engelmannii), mountain hemlock (Tsuga mertensiana), and Alaska-cedar (Chamaecyparis nootkatensis) begins to give way to fields of snow and subalpine meadows with brilliant displays of wildflowers (photographs above and below). The short growing season at this elevation means that these plants have relatively little time to produce and disperse their seeds; thus, many of them bloom at the same time, competing for animal pollinators with an incredible variety of flower colors and shapes. Several species of mammals, birds, and plants are seen at our forest stops within the park. A composite checklist of plant and animal species observed on our trips may be accessed through the link provided at the bottom of each page of this virtual fieldtrip.

Also at Paradise, we are near the foot of Nisqually Glacier (photograph below), one of several glaciers that have sculpted the slopes of Mount Rainier. Glaciers can form on peaks with perpetual snow, which is compressed under its own weight, pressing the air from between the particles. Gravity causes the resulting mass of ice to flow downhill. When snowfall exceeds snowmelt, the glaciers advance down the mountain slope, scouring the surface. During periods when the glacial ice is melting, water flowing from the leading edge of the glacier transports eroded material, such as "glacial flour", a fine powder ground by the movement of the glacier. The lower portion of Nisqually Glacier in the photograph below on the right is covered with dust, and the Nisqually River flows from the glacier through the U-shaped glacial valley.

From the subalpine forest of Paradise, we drive to the lower montane forest of our campsite at Cougar Rock, located southwest of the peak. The old-growth forest here is comprised of Douglas-fir (Pseudotsuga menziesii), western redcedar (Thuja plicata), western hemlock (Tsuga heterophylla), and firs (Abies). After supper, we hike to the nearby Nisqually River (a few kilometers downstream from Nisqually Glacier) and its tributary, Paradise River (photographs below). Streams create openings in the forest canopy that allow deciduous trees, such as red alder and vine maple (Acer circinatum), to grow along their banks, where they can escape the shade of the conifers to harness the summer sunlight and obtain water from the alluvium. Because the Nisqually River flows from Nisqually Glacier, it has a cream color from the glacial flour suspended in the water. Paradise River, on the other hand, does not flow from a glacier, so it has clear water. The rocks in its fast-flowing water are home to tadpoles of tailed frogs (Ascaphus truei) and other aquatic organisms.