MOUNT RAINIER The Forest Communities of Mount Rainier National Park

A major objective of community or habitat type classifications is the development and extrapolation of information on management problems and development potential. Because areas identified as belonging to the same habitat type are viewed as having comparable environments, responses to specific management practices should be similar. Hence, it is reasonable to extrapolate management experience or research results from one area of the same habitat type to another.

Qualitative data on characteristics relevant to management, such as productivity and soil drainage, were collected during the development of the habitat type classification at Mount Rainier. Although quantitative information and detailed studies of effects of various practices or uses stratified by habitat type would be desirable, the qualitative data provide some guidance on the potential of different habitat types for Park use and development.

Some characteristics of the Mount Rainier habitat types relevant to National Park Service management are summarized in Table 20. Each characteristic will be discussed briefly in the following paragraphs. The reader should note that these are broad, qualitative characterizations. Detailed, quantitative data on management characteristics of community types, such as productivity and wildlife potential, are being collected on the Gifford Pinchot and Mt. Baker-Snoqualmie National Forest lands adjacent to the Park (Henderson and Peter 1981, Brockway et al. 1983). This large body of information should be generally applicable to the community types within the Park.

Physical Conditions

The three factors considered under physical conditions are length of growing season, soil drainage, and depth and duration of snowpack. These features are obviously relevant to management, for appraising the development potential of a particular site for a campground or trail, for example.

Table 20. Management-related features of the various forest habitat types at Mount Rainier National Park.

Growing season can be measured in a variety of ways, but one common method in the Pacific Northwest is a scheme for summing temperatures over a given threshold, referred to as the "growing season temperature growth index" (GSTGI) (Greene and Klopsch 1985). Temperature data gathered from a few stands (Greene and Klopsch 1985) allow us to scale the qualitative ratings shown in Table 20: long growing seasons have GSTGI values of from 55 to 65, medium growing seasons have values from 40 to 60, and short growing seasons have values from 25 to 50. Note that any measure of growing season, whether by temperature growth index or frost-free period, will vary substantially from year to year. Sites with long and medium growing seasons typically have over 290 frost-free days, whereas those with short growing seasons have 200 to 290 days (Greene and Klopsch 1985).

Soil-drainage ratings are based on observations of conditions within soil pits dug in each habitat type. Excessive drainage indicated coarse-textured soils that have low water-holding capacity; droughty conditions are normally expected on such sites. Well-drained sites have no features suggesting poor or excessive soil drainage. Poorly drained soils have morphological features indicating poor drainage, such as gleyed soil horizons, and soil pits sometimes contained standing water due to perched water tables.

Three ratings are provided for depth and duration of snowpack (Table 20). Tsuga heterophylla habitat types are shown as having an intermittent snowpack; that is, the snowpack will typically come and go during the course of a normal winter. The bulk of the Abies amabilis Zone has a moderate snowpack, a permanent winter snowcover that will typically reach depths of 1 to 2 m. Deep snowcover refers to areas with a permanent winter snowpack that attains depths of 2 to 5 m or more and persists until late June or July. Approximate values for average winter snow depth can be obtained by observing the growth of lichens on tree trunks; most of the larger foliose species are unable to grow at heights where they are subject to extensive snow burial.

Biological Conditions

Factors rated under biological conditions are productivity, plant diversity, potential for specialized wildlife, and occurrence of specimen trees or groves (Table 20).

Site productivity can be indexed in a variety of ways, but the only quantitative measure available from this study is site index, the height to which dominant trees grow during a given period of time. All of the habitat types with high or very high productivity ratings are on moist to wet sites at low to middle elevations (Table 20); productivity generally approximates a Site Class I or II for Pseudotsuga and Class I for Abies procera. Sites of medium productivity approximate a Site Class III or IV for Pseudotsuga and II and III for Abies procera. Low productivity sites approximate a Pseudotsuga Site Class V or Abies procera Site Class IV. Productivity is so low on the Pseudotsuga menziesii/Arctostaphylos uva-ursi sites that forests often lack a closed tree canopy.

Plant diversity ratings are based on the numbers of vascular plant species typically found within forest stands growing on each habitat type. Moist, lower elevation habitats typically contain the largest number of species. In at least some other parts of the Northwest, dry habitats also tend to have high diversity (e.g., Zobel et al. 1976); this is not the case at Mount Rainier, where the driest forest habitats are typically the depauperate Gaultheria shallon types (Table 20). Relatively high species diversity is also encountered on the Chamaecyparis nootkatensis/Vaccinium ovalifolium Habitat Type, which typically includes boggy areas within a forest matrix. Very rich, meadow-like communities characterize early successional stages on the Abies amabilis/Rubus lasiococcus Habitat Type; the diversity of these communities contrasts with the moderate levels of diversity typical of closed forest stands on the same habitat type.

Special wildlife features considered include occurrence of old-growth species, winter habitat for ungulates (elk and deer), and habitat for amphibians (Table 20). Temperate old-growth forests in the Pacific Northwest have been identified as the preferred (and, in some cases, essential) habitat for an array of bird, mammal (including bat), and amphibian species (Franklin et al. 1981). Much of the forest at low to middle elevations within Mount Rainier National Park is excellent habitat for these old-growth-related wildlife. Extensive areas of appropriate age classes and forest structures are present, and suitable habitat types included the very widespread Abies amabilis/Vaccinium alaskaense type. Detailed studies of vertebrate populations in old-growth as well as younger forests are currently underway and should provide much additional information on their distribution within the Park. The most prominent winter habitats for ungulates are the productive, valley-bottom habitat types, although the relatively warm and dry Tsuga heterophylla/Gaultheria shallon habitat also receives considerable use. Amphibians are most common on habitat types normally associated with water bodies that are essential to their reproduction.

Trees or groves of trees of unusual size and age are of special interest to the visitor; these usually occur in old-growth stands on high productivity habitat types (Table 20). The Oplopanax and Polystichunn habitats are primary sites for outstanding specimens of Pseudotsuga nnenziesii and Thuja plicata, for example (Fig. 39). The largest Tsuga heterophylla and Abies amabilis will also be found there. Superlative specimens of Abies procera are encountered on the Abies amabilis/Tiarella Habitat Type. Some of the most impressive specimens of Chamaecyparis nootkatensis will actually be found on a low productivity habitat type, the Abies amabilis/Rhododendron albiflorum (Table 20). Specimen trees are also found on the very widespread Abies amabilis/Vaccinium alaskaense Habitat Type.

Figure 39. Superlative specimen trees of Pseudotsuga and Thuja are characteristic of the moist, alluvial and lower slope habitat types.

Potential for Disturbances

Potential disturbances to forests from wildfire, insects and plant diseases, and wind vary by habitat type (Table 20).

Important correlations may exist between fire frequency and habitat type as discussed in the previous chapter (Table 20) (Hemstrom 1982). Low-risk habitat types are those occurring on moist habitats that are, in turn, generally located in valley-bottom environments. These include the two Oplopanax, Polystichum, and Vaccinium alaskaense Habitat Types. Habitat types that characterize warmer, drier environmental conditions, such as the Gaultheria, Berberis, and Xerophyllum types, have substantially higher fire frequencies. Most of the high-elevation types have moderate levels of fire risk. The Abies lasiocarpa/Valeriana sitchensis Community Type is a significant exception; this community has the highest fire frequency (275 years) of any type studied in the Park (Hemstrom 1982).

Many forest insects and plant diseases will probably prove to be correlated with vegetation types once detailed studies have been conducted. Little information is currently available, however (Table 20). Gaultheria habitats were noted as having high levels of dwarf mistletoe (Arceuthobium spp.), especially in the Tsuga heterophylla. Some other habitats appeared to have higher levels of bark beetles (Dendroctonus spp.) in Pinus spp. and Pseudotsuga menziesii.

Natural windthrow is highest on habitat types that have moist to wet soils. Uprooting of trees has been observed as common on permanent sample plots in Oplopanax types (see footnote 3). Sites with high water tables at high elevations are also more vulnerable to uprooting.

Development Potential

Habitat types are rated for development potential (e.g., camping areas and trails) on the basis of their resistance and resilience. Resistance refers to the ability of a habitat to tolerate human impacts, such as trampling, without undergoing major changes in community composition and structure. Resistance generally reflects the "toughness" of the vegetative cover. Resilience refers to the ability of vegetation on a habitat to recover once it has been destroyed or severely disrupted. Resilience often reflects the inherent productivity of a habitat.

Communities on high productivity sites dominated by herbaceous understories (TSHE/OINYM, TSHE/ACTR, and ABAM/TIUN) tend to have low resistance and high resilience. Understories are easily damaged by human use due to the fragility of many species but have inherently high rates of recovery. The Oplopanax communities are somewhat more resistant to use because of durable shrub layers that also tend to discourage human movement.

The bulk of the communities at Mount Rainier have moderate to high levels of resistance to developmental impacts and moderate to low levels of resilience (Table 20). This is because the shrubby ericaceous understories are generally composed of species that can tolerate moderate impact levels. Once destroyed, however, recovery can be relatively slow due to slow reestablishment and growth of plants. This is a particularly serious problem on sites that have deep, persistent snowpacks (e.g., CHNO/VAOV and ABAM/RHAL). Sites on glacial outwash and lahars, including PSME/ARUV habitats, typically have understories that include species easily damaged by trampling (e.g., lichens and mosses) and very low rates of recovery due to severe site conditions. Longmire Campground provides an example of such a habitat.