Vegetation
Alpine Meadows with Intermingled Forests
This association is around the rim of Crater Lake and extends northward to Pumice Desert and southward to Union Peak and Crater Peak. Precipitation ranges from 40 to 80 inches per year, occurring mainly as snow. The average annual temperature is very cold (38 to 42 degrees F), and the growing season is very short (less than 30 days). Except on southern exposures, the snowpack usually remains on the ground well into summer.
The meadow areas of this association are parklike, and they are surrounded by forest areas of mountain hemlock (Tsuga mertensiana) and whitebark pine (Pinus albicaulis). These meadow areas are strongly correlated to soil types and are thought to be relatively permanent, although the structure of the historic plant community may have been different (Lynch, 1998). The boundaries between the forest areas and the meadow areas in this association generally are abrupt, and rarely are there significant intrusions of tree species in the meadow areas. Historically, a long period of time has elapsed between catastrophic fires in areas of this association. Local Indian tribes, who used these areas frequently in summer, may have set fires to freshen the vegetation to attract big game.
The rangeland ecological sites in this association consist of grass-dominated meadows, sedgedominated swales, and very sparsely vegetated alpine deserts. The meadows have the greatest diversity of plant species; thus, they also have higher value as wildlife habitat. The pumice flats and deserts are nearly barren, but they support some low-growing, compact plants that have large taproots (Franklin and Dyrness, 1973). All of the rangeland ecological sites in this association have cryic soil temperatures and a udic moisture regime.
The Pumice Desert ecological site occurs at slightly lower elevations northwest of the rim. This site supports very sparse vegetation comprised of nearly equal amounts of marumleaf buckwheat (Erioginum marifolium), western needlegrass (Achnatherum occidentale ssp. californicum), and Brewer’s sedge (Carex breweri). This site is in depressional areas surrounded by lodgepole pine forests. The soil surface consists mainly of cinder fragments. Horn concluded that a severe climatic regime characterized by widely varying daytime and nighttime temperatures and low soil fertility resulted in the paucity of vegetation (only 14 species have been observed) (Franklin and Dyrness, 1973). Soil moisture is available to plants throughout the growing season.
The Ashy Alpine Desert ecological site is at the higher elevations (see fig.1, page 97). It is associated with the Ashy Alpine Meadow and Ashy Alpine Swale ecological sites and may support interspersed areas of mountain hemlock (Tsuga mertensiana) and whitebark pine (Pinus albicaulis). This site supports very sparse vegetation because of the rock and pararock fragments on the thin soil surface, an extremely wide range of diurnal temperatures, and low soil fertility. The site is extensive on some south- and southwest-facing slopes. It can occur on slopes where the snowpack stays well into summer in most years, limiting germination and establishment of plants. The dominant plant species are small, shrubby Shasta buckwheat (Erigonium pyrolifolium) and Newberry knotweed (Polygonum davisiae), which has a distinctive late-season red color.
The Ashy Alpine Meadow ecological site is the most widespread of the alpine sites. It is a relatively productive grassy meadow site that supports dominantly western needlegrass (Achnatherum occidentale ssp. californicum), Hall’s sedge (Carex halliana), bottlebrush squirreltail (Elymus elymoides ssp. elymoides), and shrubby Bloomer’s goldenweed (Ericameria bloomeri), which has brilliant yellow flowers in July and August. This site occurs around the caldera rim, especially in the southern, southwestern, and southeastern areas, and extends to areas around Union Peak and Crater Peak to the south. It is associated with the Ashy Alpine Desert and Ashy Alpine Swale sites. It is arrayed in a parklike setting surrounded by and interspersed with stringers of mountain hemlock. It provides important forage in summer for large ungulates and for rodents, which attract raptors.
The Ashy Alpine Swale ecological site occurs around the caldera rim in association primarily with the Ashy Alpine Meadow and Ashy Alpine Desert sites (see fig. 2, page 98). This site occurs in small depressions and on flat terraces. The soils in this site have a slightly impermeable subsoil. Snowpack and snowmelt tend to collect on the soils. Areas of this site are patchy and support dominantly Brewer’s sedge (Carex breweri) or Parry’s rush (Juncus parryi) with minor amounts of western needlegrass (Achnatherum occidentale ssp. californicum) and bottlebrush squirreltail (Elymus elymoides ssp. elymoides). Brewer’s sedge and Parry’s rush can occur together or separately, depending on the length of time that the snowpack stays on the surface. Parry’s rush tends to grow in areas that are colder and wetter and have longer periods of ponding, and Brewer’s sedge tends to grow in areas that dry out quicker.
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