Volume XXIII - 1992
90th Anniversary Edition

Much of the Crater Lake National Park is covered in forest. One visible exception is the Pumice Desert on the road to the park's north entrance. At first glance this 5 1/2 mile square, nearly flat opening appears to be quite barren except for a few scattered lodgepole pine (Pinus contorta). A closer look reveals that many forms of life, including several mammals, use this landscape as a habitat.

At a mean elevation of 5,960 feet, the Pumice Desert is in the Klamath River drainage basin. Yet it is but two miles from the Umpqua River and Rogue River tributaries. Elizabeth Mueller Horn studied the ecology of the Pumice Desert and described the vegetation, which largely consists of herbaceous plants with very sparsely scattered lodgepole pine. She found only 14 plant species with total cover of 4.6 percent. All plants except the lodgepole pine are small herbaceous or woody stemmed forms with various adaptations for surviving in the absence of summer surface moisture and relatively high temperature. The poorly developed soil is relatively porous and deficient in several minerals, a further cause of the depauperate flora. The resulting lack of cover increases daytime summer temperatures, creating a relatively unique park habitat resembling parts of the Great Basin Desert to the east.

Interestingly enough, several animals are adapted for living in the Pumice Desert's rather harsh micro-habitat. Mammals are an excellent example of the way in which some animals cope with the conditions of extreme temperatures and seasonally restricted food and water. The mammals that occupy the Pumice Desert are either well adapted for living in these restrictive conditions, or are highly mobile, and use the area on a temporary basis, or are simply passing through during movement to more preferred habitat. Field studies by one of us (Monical) indicate that only three mammal species appear to be permanent residents, far fewer than in other park habitats. The Great Basin pocket mouse (Perognathus parvus) and the deer mouse (Peromyscus maniculatus) occur in significant numbers. One summer's live trapping (168 traps set for ten nights) resulted in the capture of 54 individual pocket mice and 46 deer mice.

The Great Basin pocket mouse, a seed-eating specialist, is common in the high desert habitat of western North America. It carries food in its fur lined cheek pouches for storage in a burrow. The ability to metabolize moisture from its food allows the pocket mouse to survive with no free water This nocturnal species also closes its burrow during the day to help maintain a moist environment. When conditions become too severe, it will estivate in the summer or become inactive during the winter.

The deer mouse is the park's most ubiquitous species, utilizing many different habitats. A highly omnivorous animal, it is able to survive on a variety of vegetative parts, insects, and has even been known to eat other small mammals. Though mostly nocturnal, the deer mouse at times can be seen just before dark when it begins its search for food. An additional adaptation leading to its continuing survival in harsh conditions is its high reproductive rate.

A third, less abundant, resident is the western pocket gopher (Thomomys mazama). Its mounds are seen on the periphery of the desert near the forest edge, where the texture of the pumice soil is more conducive to its underground habits. Gophers are active in the winter and sometimes fill their above-ground burrows under the snow with soil. After melt, these serpent-shaped ridges are evidence of the previous winter's activity.

Other captured or observed rodents, considered transients, are the yellowpine chipmunk (Tamias amoenus), golden mantled ground squirrel (Spermophilus lateralis), bushy tailed woodrat (Neotoma cinerea), and porcupine (Erethizon dorsatum). It is also likely that snowshoe hares (Lepus americanus), mule deer (Odocoileus hemionus), and perhaps elk (Cervus elaphus), occasionally venture into this area of marginal habitat. Some species of bats that roost in the nearby forest use the open areas for foraging. Predators are rare but could include the red fox (Vulpes vulpes), coyote (Cants latrans), ermine (Mustela erminea), and long- tailed weasel (Mustela frenata). The pronghorn antelope (Antilocapra americana), sometimes sighted in the park, is known to use open areas such as the Pumice Desert. This location represents one of the westernmost extremes of the current range for this species, usually a Great Basin inhabitant.

Mammals utilize the Pumice Desert for a variety of reasons, even though the harsh environmental conditions preclude most as residents. The presence of the Great Basin pocket mouse as a permanent inhabitant there creates a unique combination of species for Crater Lake National Park.

L. Howard Crawford, Nature Notes, Vol. VIII, No. 3, September 1935.