By Jeffrey P. Repp, State rangeland management specialist, and Craig M. Ziegler, State forester, Natural Resources Conservation Service.
Crater Lake National Park is in three major land resource areas (USDA, 1981). A major land resource area (MLRA) is a geographically associated land resource unit that is characterized by a particular pattern of soils, climate, water resources, and land uses. Most of the park is in the Olympic and Cascade Mountains area (MLRA 3). The drier eastern part is in the Cascade Mountains, Eastern Slope, area (MLRA 6), and the extreme southwestern corner is in the Siskiyou-Trinity area (MLRA 5).
The part of the park in the Olympic and Cascade Mountains area (MLRA 3) is nearly all forested, but there are areas of open alpine meadows and swales and rock outcroppings. Typical tree species are mountain hemlock (Tsuga mertensiana), Shasta red fir (Abies x shastensis), whitebark pine (Pinus albicaulis), and lodgepole pine (Pinus contorta) and to a lesser extent western white pine (Pinus monticola), subalpine fir (Abies lasiocarpa), and white fir (Abies concolor). The understory vegetation is highly variable. The elevation, precipitation, type of soil, and overstory canopy influence the composition and abundance of the understory vegetation. Most of the precipitation is received in the form of snow.
The soils in the Cascade Mountains, Eastern Slope, area (MLRA 6) consist dominantly of ash and pumice. These soils support forests that have varying degrees of density. Ponderosa pine (Pinus ponderosa), western white pine, Shasta red fir, white fir, and lodgepole pine are the most common tree species. The understory plant cover varies depending on the amount of precipitation and the overstory canopy cover. In the northeastern part of the park, sedges and grasses are most abundant, but in the southeastern part, brush and sedges are most common.
The small part of the park in the Siskiyou-Trinity area (MLRA 5) also is forested. The dominant tree species is Douglas fir (Psuedotsuga menziesii) with some white fir and sugar pine (Pinus lambertiana). The composition and abundance of the understory vegetation can be highly variable. Because this area is at the lower elevations and is characterized by a warmer climate, the abundance of the understory Crater Lake National Park, Oregon 91 generally is higher than that in MLRA 6. Precipitation is received mainly in the form of rain, but some snow falls in winter. Rainfall generally is distributed throughout the year, but little is received in summer.
The rangeland ecological sites in the park can be placed into two broad historic plant associations—alpine meadows with intermingled forests and wetlands with intermingled forests. The forestland ecological sites can be placed in six broad historic plant associations—whitebark pine, mountain hemlock, Shasta red fir, ponderosa pine/fir, lodgepole pine, and Douglas fir. The location and distribution of these associations is shown on the General Vegetation Map included in this survey. A discussion of each plant association follows.