Identification | Biology | Damage ID| Management | Handling

Damage to Landscapes and Crops

Mountain beavers damage commercial coniferous tree species in western Washington and Oregon. The damage period extends to about 20 years after planting. The major losses occur from cutting tree seedlings during the first year after planting. Secondary damage occurs during the next 5 years to surviving tree seedlings, followed by stem girdling and root damage for the next 10 to 20 years. Increased need for weed and brush control and occasional replanting costs add to the economic losses caused by mountain beavers.

Damage to conifer seedlings is identified by angular rough cuts on stems 1/4 to 3/4 inches (0.6 to 1.9 cm) in diameter. Mountain beavers climb larger trees and cut stems near the tips. Limbs are often cut a few inches from the stem. Small trees are usually cut near ground level while others may be cut several feet up the stem. Seedling damage occurs primarily in winter and early spring, but often continues throughout the year.

Most stem-girdling damage is at the base of 3- to 6-inch (7- to 15-cm) diameter stems. Girdling damage can be distinguished from that caused by bears or porcupines in that mountain beavers do not leave pieces of bark scattered on the ground and they cut the bark smoothly along the edges. Girdling damage to older stems is more difficult to distinguish, but it can be verified by examining burrows near tree trunks where fresh girdling can be seen on the roots.

Root girdling may occur at any age, but small roots are usually cut instead of girdled. Trees with stems over 6 inches (15 cm) in diameter may die due to extreme root girdling. Root girdling may allow tree root pathogens to become established in individual trees and spread to other trees. It occurs in winter and spring, and may occur in other seasons.

Mountain beaver damage in 10- to 15- year or older stands appears to be increasing and is of great concern because the crop trees are often selected at this time for precommercial thinning. Stem and root girdling may affect over 50% of the trees in a stand. Managers cannot achieve proper spacing in these damaged stands, and damage may continue on trees left as crop trees.

Damage to coniferous species is considered detrimental to forest production and can have long-term effects on habitats. This damage to commercial crops and other vegetation, however, does provide diversity of cover for other wildlife.