American porcupine,  Erethizon dorsatum  

Fig. 288  Stem girdling on larch due to porcupine feeding.	Fig. 289  Porcupine teeth marks left in sapwood.	Fig. 290   Top kill resulting from upper stem girdling.

Distribution:  Throughout B.C., except for Vancouver Island and the Queen Charlotte Islands.

Tree Species Attacked: Sitka spruce, ponderosa pine, Douglas-fir, and western hemlock are attacked, with sapling-sized and larger trees being particularly susceptible. All other conifer species, of all ages, are affected less frequently.

Signs & Symptoms: Porcupines damage trees during the winter when they feed on the inner bark. They discriminate by taste and will select individual trees for feeding, while leaving other nearby trees undamaged except for a small test feeding patch. Bark is gnawed from trees rather than stripped. Basal girdling is more common on smaller trees, while debarking of the upper stem and major branches occurs on larger saplings to mature trees. Symptoms are generally evenly distributed on the upper bole and throughout the crown of these older trees. The sapwood is always deeply gnawed and prominent vertical and diagonal toothmarks approximately 2.5 mm wide can be seen. Small strips of bark may be found around the base of attacked trees. Some branch cutting may also occur. Attacked trees may display characteristic bushy crowns and spike-tops as a result of top girdling. Tracks are not prominent during the summer months but may be seen during winter in the snow, in the form of a trough-like trail that shows a drag mark from the tail and brush marks from the quills. Abundant droppings are usually found around recently attacked trees. Droppings are single or linked together in short chains. They are 2.5 cm long, narrow and curved, and have rounded ends.

Damage: Porcupine attacks on conifers can cause serious losses. Scattered mortality can occur over fairly extensive areas. Trees die when the lower portion of the stem is girdled. Annual mortality rates are estimated to be about 1% per year of the hemlock and spruce component in heavily damaged stands. Top kill, deformity, and reduced growth rate result from feeding activities on the upper stem and in the crown.

Similar Damage: Stalactiform blister rust or atropellis cankers on mature lodgepole pine are sometimes mistaken for older porcupine damage. If close inspection is possible, look for the toothmarks of the porcupine.

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Contact Tim Ebata if you have comments on the presentation of this information.

BC Ministry of Forests
Forest Practices Branch
P.O. Box 9513 Stn. Prov. Gov.
Victoria, BC
V8W 9C2

Section phone: (250) 387-8739
Section fax: (250) 387-2136

Last updated March 04, 2002