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Forests for one plant species may not work for another. For example, the mycorrhizal fungi of bearberry and Pacific madrone are compatible with Douglas fir and pine, but are incompatible with vine maple and other trees (Proctor, et al., 1980). As a result, seedlings of Douglas fir and pine survive and grow easily in woods of bearberry and madrone, but seedlings of vine maple must compete for nutrients with their bare roots, often unsuccessfully. Clearly, these lock-and-key partnerships can influence forest composition. In addition to the plants, many small mammals benefit from mycorrhizal fungi. When their underground spores mature, the fungi give off a new odor that attracts squirrels, chipmunks, mice, voles, and shrews. About 80% of these consume fungi as a dietary staple, and many feed extensively on truffles and other mycorrhizae-forming species, whose spores pass through their bodies and scatter intact throughout the forest, thus inoculating the soil and litter to the benefit of future seedlings (Maser and Trappe, 1984). Some rodents, such as the California red-backed vole [. . .] are so dependent on the fruit of the mycorrhizal fungi that they cannot survive in a recent clearcut. [. . .] Plant roots themselves are quite remarkable in the way in which they can chemically enhance nutrient uptake. Since many of the dissolved nutrients are positively charged when dissolved in the soil water (potassium, calcium, magnesium), they are chemically attracted to the negatively charged soil clay particles and organic colloids. To absorb these minerals a plant must somehow pull them off the particles and into solution. The roots accomplish this by secreting acids into the soil. The acids release hydrogen ions, which stick even more tightly to the soil particles than the nutrients. So as the hydrogen ions attach, they displace the nutrients, which are then free to dissolve in the interstitial water, and eventually move into the root hairs. This relationship between acid and minerals has played a central role in the creation of a special kind of soil in the Northwest. In general, soil acids loosen nutrients that then flush or “leach” with rainwater downward to deeper soil layers. Here they may enter plant roots or diffuse into the groundwater, which washes them out of the forest into streams and eventually to the estuaries. [. . .] In the Northwest, a further major source of acid is the conifer foliage, which exudes more acids into the forest floor during decomposition than do deciduous trees. Soil acidity, coupled with the heavy Northwest rains and cool climate, have combined over thousands of years to create “podzolic” soils. Such soils display only a thin layer of organic material near the surface, and an accumulation of mineral nutrients and other materials at deeper levels due to leaching (Spurr and Barnes, 1980). Most leaching, however, occurs after disturbances such

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as fires, clearcuts, and landslides, when there are no live roots to capture the nutrients at the soil surface before they sink out of reach. In an old growth forest, nutrient flow is extremely conservative, as nutrient loss and input are extremely small, and the majority of minerals taken up by a plant have only recently been liberated from decomposing litter. Large old growth trees help sustain and enhance the nitrogen economy of low to mid-elevation forests. The microclimate created by the large canopy encourages the growth of several nitrogen-fixing lichens uncommon in young growth. The most important, Lobaria oregana, makes up about half the biomass of all lichens and mosses growing on live trees in mid-elevation hemlock forests; also present are L. pulmonaria, Pseudocyphellaria rainierensis, and Peltigera aphthosa (Franklin, et al., 1981). These lichens pull enough nitrogen out of the air to manufacture about 2-5 lbs/acre of nitrates per year, which enter the soil from fallen, decomposing lichens (Franklin, et al., 1981). These lichens are an important source of protein (synthesized from the nitrogen) for several mammals. The northern flying squirrel feeds preferentially on lichens during the winter when seeds are scarce; both elk and deer feed heavily on lichen litter during winter starving times, especially in the Cascades (Harris, 1984). Habitat. Typical heights of old growth conifers greatly exceed those of any other forest on earth. Since animal habitat is three-dimensional, this height translates into an immense habitat volume. As old trees die and an understory of both conifers and hardwoods develops, a tremendous diversity of crown heights results, and with it a diversity of birds and arboreal mammals. Partly because of this, western Oregon contains more bird families than any other region in North America, and unusually large numbers of resident mammal species (Harris, 1984). The important triumph of a large dense canopy is the milder air temperatures within it. In the west Cascades, when the canopy is wet, the air temperatures inside range from 32°F in the winter to 60°F in the summer; in dry weather the range is 14°F to 104°F. This regime ensures the survival of “epiphytes” (plants, usually lichens and mosses, growing on the trees), and insects, birds, and mammals either because of the mild microclimate or the nourishment offered by the epiphytes or both (Franklin, et al., 1981). [. . .] For example, the dominant, nitrogen-fixing lichen Lobaria oregana, which flourishes on upper surfaces of branches and twigs, is active when wet and dormant when dry. So its vulnerable active state switches on only during mild temperatures, and it avoids lethal extremes (Franklin, et al., 1981). Other epiphytes probably enjoy similar lifestyles; in any case, a total of 30-40 lbs

Profile for University of Puget Sound

Bookends Reader  

Welcome new students! This reader is a collection of readings from and about Puget Sound and that will be at the heart of the Bookends orien...

Bookends Reader  

Welcome new students! This reader is a collection of readings from and about Puget Sound and that will be at the heart of the Bookends orien...