MOUNT RAINIER The Forest Communities of Mount Rainier National Park

The diversity of the flora and fauna in Mount Rainier National Park reflects the Park's great environmental and elevational range. General features of the vegetation, as understood from past studies, are briefly reviewed here. Detailed discussions of disturbance and succession are found in Chapter 7.

Vegetation

Closed coniferous forests and subalpine and alpine meadow communities are the major plant formations in the Park. The forests occupy about 60 percent of the Park landscape, extending to elevations of about 1600 m (5,250 ft) on the western and 2000 m (6,000 ft) on the northeastern slopes of the volcano. Parklands (mosaics of forest patches, tree clumps, and meadows) extend above the forest line for another 300 m (1,000 ft) (Fig. 6). Ice, permanent snowfields, rock, and barren ground predominate above about 2500 m (8,200 ft).

Figure 6. Parkland mosaics of tree stringers and patches and subalpine meadows extend about 300 m (1,000 ft) above forest line with permanent snowfields, rock, and barren ground common above the parkland. Headwaters of Nickel Creek.

The forests of the Park are part of the coniferous forest formation of the world. Regionally, these forests have been described by dominance of Pseudotsuga menziesii within Tsuga heterophylla-Thuja plicata climaxes (Franklin and Dyrness 1973), and as being part of the Tsuga heterophylla and Tsuga mertensiana ecogeographic provinces (Daubenmire 1978). These stands are known for their density, productivity, nearly complete conifer dominance, and the size and longevity of the dominant tree species. Most coniferous genera find their largest and often longest lived representatives in these forests, including Pseudotsuga, Tsuga, Abies, Chamaecyparis, Picea, Pinus, and Thuja (Fig. 7). Forest productivity and the massive accumulations of wood relate to the attainable sizes and ages as well as the relatively moderate winter temperatures and dry summers characteristic of the region (Waring and Franklin 1979).

Figure 7. This massive 1,000-year-old Douglas-fir grows in a stand of the Abies amabilis/Vaccinium alaskaense habitat type along the upper Ohanapecosh River.

Variation in the forests of this region relate mainly to three factors: temperature regime, moisture (including snow) regime, and the length of time the forest has gone undisturbed. Disturbance will be discussed in the next section. Temperature is primarily responsible for the strong changes in forest conditions associated with elevation; these changes are typically described as belts or zones (see, for example, Zobel et al. 1976). There are three forest zones in the Park: Tsuga heterophylla, Abies amabilis, and Tsuga mertensiana (Franklin and Bishop 1969). The Tsuga heterophylla Zone is a part of Daubenmire's (1978) "Temperate Mesophytic Forest Region" and "Tsuga heterophylla Province" which he describes as having the most luxuriant conifer forest in the world. The Tsuga mertensiana Zone is a part of the "Subarctic-Sublpine Forest Region" and "Tsuga mertensiana Province" which extends from California to Alaska (Daubenmire 1978). We consider the Abies amabilis Zone to be cool temperate rather than subalpine; it is not explicitly recognized by Daubenmire (1978).

Substantial permanent winter snowpacks are characteristic of both the Abies amabilis and Tsuga mertensiana Zones, with much greater depths and durations in the latter. In both zones depth and duration of snow pack are important factors differentiating forest community types (Brooke et al. 1970, Long 1976). Moisture regime during the dry summer months appears to be the most important factor affecting the forest patterns in the Tsuga heterophylla Zone (Zobel et al. 1976).

Forests in the Park have been the subject of numerous general accounts, including those of Plummer (1900), Foster (1911), Brockman (1933, 1947, and 1949), and Franklin and Bishop (1969). Brockman (1931) also did a classification of forest cover types and a map of the Park. Most of these accounts cover only the broad patterns of tree species occurrence. The major tree species in the Park are Abies amabilis, Abies grandis, Abies lasiocarpa, Abies procera, Chamaecyparis nootkatensis, Picea engelmannii, Pinus albicaulis, Pinus contorta, Pinus monticola, Pseudotsuga mensiesii, Tsuga heterophylla, Tsuga mertensiana, and Thuja plicata. Rare tree species include Picea sitchensis in the Carbon River drainage and Pinus ponderosa on the east side of the Park.

In addition, several detailed studies have examined the vegetation in areas adjacent to the Park, Franklin (1966) provides a general forest-association-habitat type classification for the southern Washington-northern Oregon Cascade Range, including Mount Rainier. Thornburgh (1969) includes considerable autecological study of tree species as well as information on stand ages and dynamics. Long (1976) reports the forest communities found in the Cedar River drainage thirty miles north of the Park. Henderson and Peter (1981) and Brockway et al. (1983) provide comprehensive classifications of the plant associations and habitat types in the White River drainage and on the Gifford Pinchot National Forest, respectively, both locales bordering the Park. All five of these papers include considerations of forest succession, especially the climax role of Abies amabilis and its relation of succession to other tree species. Other papers of interest include Higinbotham and Higinbotham (1954) on forest mosses; del Moral et al. (1976) and del Moral and Watson (1978) on the central Washington Cascade Range community mosaic; and Kotor (1972) on the ecological relationships of Abies amabilis.

The subalpine and alpine meadow vegetation is well known for its diversity and aesthetic qualities. Scientific studies include those of Henderson (1973) and Hamann (1972) on the plant community types, Franklin et al. (1967) on meadow invasion by trees, and Edwards (1980) on visitor impacts in alpine regions. Major categories of subalpine meadows are (1) Heather-huckleberry (Phyllodoce-Cassiope-Vaccinium), (2) Black sedge (Carex nigricans), (3) Green fescue (Festuca viridula), lush herbaceous (Valeriana-Veratrum), and "rawmark" or early successional community (Saxifraga tolmei). The distributional patterns of these communities are determined largely by the depth and duration of snowpack.

Disturbances to Vegetation

Elapsed time since the last major disturbance largely determines stage of vegetational succession and is the third important factor influencing the composition and structure of the existing forests in the Park. Agents that disturb or destroy forests include wildfire, snow and rock avalanches, volcanic eruptions, mudflows, floods, and wind. Following a severe disturbance, a site is typically occupied by a series of non-forested communities (for example, herb- and shrub-dominated types) before forest cover is reestablished. The initial or pioneer forest often includes, and may be dominated by, shade-intolerant tree species such as Pseudotsuga menziesii and Pinus spp. With time, such light-requiring species are gradually replaced by shade-tolerant species that can reproduce in the understory of a closed-canopy forest. Tsuga heterophylla and Abies amabilis are examples of shade-tolerant species capable of forming self-perpetuating or climax types that remain constant in composition.

The history of disturbance to forests in the Park has been reconstructed by Hemstrom (1979) and Hemstrom and Franklin (1982); a map showing the major forest age classes in the Park is included as Plate 2. Wildfire has been the most important forest-destroying agent near Mount Rainier and has affected all but a small fraction of the forest area during the last 1,000 years. Some of the wildfires appear to have been very large (>10,000 ha) and affected several quadrats of the Park. The fire history is discussed in detail in Chapter 7.

In recent times, portions of the Ohanapecosh drainage burned in 1803 and much of the Cowlitz drainage burned in 1856 and again in 1866 (Plummer 1900). Burns occurred on Crystal Mountain and Sourdough Mountain in 1858, in Sunset Park in 1930, and at Shriner Peak in 1934. A long natural fire rotation (around 465 years) is indicated for the Park, although the expected fire frequency ranges widely with local site conditions (Hemstrom 1982). There are correlations between major episodes of fire and periods of prolonged drought.

The rate of revegetation following wildfires is highly variable and depends on many factors, including availability of seed source and local site conditions. Single wildfires often regenerate rapidly from residual trees, but forests are often slow to reclaim areas burned two or more times within a few decades (Franklin and Dyrness 1973). Both residual and peripheral seed sources are lost in reburns, along with any existing regeneration. Sites with harsh environments, such as droughty south slopes or cold, snowy habitats, typically regenerate more slowly than sites with favorable moisture and temperature conditions (Fig. 8).

Figure 8. Forest reestablishment is typically slow on harsh sites and following multiple wildfires; both conditions exist on this site near Louise Lake, which is still only partially forested almost 100 years after it burned (in 1886 or 1887).

Lahars and mudflows have occasionally devastated forests along lower slopes and alluvial flats (Crandell 1971). The Kautz lahar of 1947 is a conspicuous example (see Fig. 3). Mortality of large old-growth trees resulted from both physical uprooting and suffocation following root burial. Succession proceeds from initial stands of Alnus rubra, Alnus sitchensis (at higher elevations), Salix spp., Pteridium aquilinum, Epilobium angustifolium, and Anaphalis margaritacea to mature forests of various types. An example of old forests developed on lahar material can be seen at Cougar Rocks campground, where some pioneering Pseudotsuga menziesii have reached 1,000 years of age on a lahar deposit of about the same age (Crandell 1971, Hemstrom 1979).

Avalanches cause extensive forest disturbance (Fig. 9), especially at high and intermediate elevations where slope angle, anchoring vegetation, and snow accumulation patterns are susceptible (Luckman 1978). Avalanche tracks stand out on aerial photographs as their boundaries contrast sharply with the less regular fire boundaries. Avalanches rank second to fire in terms of forest area disturbed in the Park. Vegetation communities and successional dynamics on avalanche tracks have been the subject of dedicated study by Cushman (1981).

Figure 9. Snow avalanches are second only to wildfire as an agent of forest destruction; tracks may be kept clear of forest by annual avalanches or eliminate forests developed on less frequently affected tracks such as this one near Spray Park.

Windthrow may be extensive in some areas, but it is difficult to isolate from other disturbances. It leaves no distinguishing boundaries and only occasionally destroys whole stands. Other factors, such as insect kills and root rot pockets, may seriously weaken trees which then blow down. Since its effects separate poorly from those of other events, the total impact of windthrow is difficult to estimate.

Other types of disturbance include glacial advances, and river activities such as flooding and terrace cutting.

Some venerable forests in the Park have survived centuries of hazard to attain ages of more than 1,000 years (see Plate 2). Large trees over 1,000 years old (mostly Pseudotsuga menziesii and Chamaecyparis nootkatensis) sit in antiquity where portions of the Ohanapecosh, Cowlitz, Nisqually, and Carbon drainages have been protected from disturbance. The Park's oldest trees are Chamaecyparis, over 1,200 years old in the Ipsut Creek valley.

As mentioned, tree species differ in their successional roles and those have been well described for the montane forests of the Cascade Range (see, for example, Franklin 1966, Thornburgh 1969, Kotor 1972, and Long 1976). A brief overview is provided here; a more comprehensive discussion is in Chapter 6. The very shade-tolerant Abies amabilis and Tsuga heterophylla are the major climax species. The Abies generally replaces the Tsuga at higher elevations (over 1000 m or 3,300 ft) with several proposed explanations (see, e.g., Thornburgh 1969, Long 1976). Pseudotsuga menziesii, Pinus monticola, Pinus contorta, Abies procera, and Abies lasiocarpa are considered seral or pioneer species, subject to successional replacement. Thuja plicata, Chamaecyparis nootkatensis, Tsuga mertensiana, and Picea engelmannii are usually considered to be of intermediate status, perhaps capable of playing some climax role in the forest mosaic in the Park. It is important to note that almost any species can appear in early successional forests provided seed source is available. Pioneer forests on many sites can be composed of Abies amabilis or Tsuga heterophylla as well as Pseudotsuga mensiesii or Abies procera.