The Arid Timbered Subdivision of the Transition Life-zone
In Washington the Arid timbered subdivision of the Transition Life-zone is the open, pine forest. Because of the aridity of this habitat, marshes and streamside thickets are uncommon, but where habitats of this kind do occur they have a fauna distinct from that of other habitats.
The pine forest habitat includes many diurnal species, such as the red squirrel, yellow-pine chipmunk, and Columbian ground squirrel. The white-tailed deer occurs here and, for most of the year, the mule deer. Snowshoe rabbits are usually present. Near rocks the bushy-tailed wood rat is common. Mice are scarce, probably because of the open nature of the surface of the ground. A night's trapping usually yields only a few Peromyscus maniculatus.
The mammalian fauna of the marshes and streamside thickets is similar. Shrews including Sorex vagrans and Sorex obscurus are uncommon. Meadow mice, including Microtus pennsylvanicus, Microtus longicaudus, and more rarely Microtus montanus, are taken.