SummaryThe major ecological features of oldgrowth coniferous forests in the Douglas-fir region are reviewed. Special attention is given to characteristics that distinguish oldgrowth forests from managed and unmanaged (natural) young stands. The primary exemplary type is 350-to 750-year-old Douglas-fir-western hemlock forest typical of the western slopes of the Cascade Range, but other types and locales are discussed. Management techniques for maintenance of oldgrowth forests are also considered. Major conclusions are:1. Approximately 175 to 250 years are required to develop old-growth forests under natural conditions in both Coast and Cascade Ranges. Development of old growth is faster on good sites than on poor sites.2. Few plant or animal species are solely confined to old-growth forests, although many speciesincluding several vertebrates, saprophytic plants, and epiphytic lichens-find optimum habitats in such forests. Some organisms, however, may require old growth to maintain viable populations. Moreover, there are substantial differences in composition and relative abundance of species between young-and old-growth forests.3. Gross productivity is maintained at high levels in most old-growth stands, but mortality generally balances growth. Thus, the merchantable board-foot volume tends to remain constant for several centuries or gradually decreases because the amount of defect increases. Total organic matter keeps increasing because of accumulated masses of dead tree boles, mostly as down logs.4. Old-growth forests are highly retentive of nutrients; large amounts are incorporated into living and dead organic matter. Losses of limiting nutrients, such as nitrogen, are low.5. Nitrogen-fixing epiphytes are abundant in old-growth trees, and bacterial nitrogen fixation appears to be common in the large woody debris characteristic of old-growth forests.6. Small-to medium-size streams in old-growth forests depend mainly on forest litter for an energy base. These materials are invariably partially utilized before they are exported downstream.7. The structure of old-growth forest is more heterogenous than that of young forests; coefficients of variation in tree sizes are greater, and understory patchiness is much higher than in young-growth stands.6. Most of the distinctive features of old-growth forests can be related to four structural features: (1) large, live old-growth trees, (2) large snags, (3) large logs on land, and (4) large logs in streams. The structural features are related over time.9. A large, old-growth Douglas-fir is individualistic and commonly has an irregularly arranged, large, coarse branch system, and often, a long crown. It is ideal habitat for specialized vertebrates, such as the red tree vole, northern spotted owl, and northern flying squirrel, as well as nitrogen-fixing lichens.10. Large snags are valuable as habitat for a variety of vertebrates and invertebrates and as a future source of logs.11. Logs on the forest floor are important habitats for small mammals, including species that dispe...

St. Helens in the Cascade Range of Washington State erupted cataclysmically. This was a monumental disturbance event, the likes of which had not been seen since western settlement of the region. The eruption began with a massive (2.8 square km) landslide that decapitated the mountain exposing its superheated core. The ensuing explosion created a 50,000 hectare "blast zone". Superheated pyroclastic flows and numerous debris flows or lahars swept down the slopes and valleys. To the north and east of the mountain, volcanic ejecta fell over thousands of square kilometers. The scale, intensity, and synergy of these disturbances created a rich laboratory for the study of disturbance ecology (1,2).

Temperature and moisture stress of conifer saplings and needle nitrogen content of conifer saplings were measured at reference stands representing 16 forest communities in the central portion of the western Cascades province of Oregon.Most species occur over a wide range of temperature and moisture stress; many occupy a wider range of environments in the western Cascades than they do in the eastern Siskiyou Mountains of southwest Oregon. Differences between vegetation zones are reflected in a temperature index; within zones, communities are distinguished by moisture stress and, to a lesser extent, by temperature. In two cases vegetation differences appear to be related to low needle nitrogen contents. Use of complex gradients for vegetation ordination suggests certain environmental differences between communities which are contrary to the differences measured; therefore, we prefer the measured gradients over the complex gradients defined.Species diversity (the total number of vascular species) increases and dominance (Simpson's index) decreases away from moderate environmental conditions to warmer-drier and colder communities. Diversities of different strata are unrelated. Dominance is concentrated in fewer strata of the vegetation on the colder sites. However, discontinuities in the pattern of diversity with environment occur which are not related to major differences in our measured environmental indexes. Evergreenness of shrubs is highest in stands with the lowest foliar nitrogen levels.

Bierlmaler, Frederick A.; McKee, Arthur. 1989. Climatic summaries and documentation for the primary meteorological station, H.

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