Schmidt, K.N. 1990. Winter feeding ecology of the North American porcupine (Erethizon dorsatum) in an isolated population of Eastern Hemlock (Tsuga canadensis) in northeastern Minnesota. M.S. Thesis, University of Minnesota. 65 pp.
The North American porcupine, Erethizon dorsatum, is a generalist herbivore that, during winter, feeds on coniferous foliage and the inner bark of conifers and hardwood trees. Winter feeding by porcupines may sometimes cause the decline or mortality of trees due to girdling of the bole and limbs or defoliation of the crown. In the north-central and northeastern portion of its range, the porcupine often selects the bark or foliage of eastern hemlock, Tsuga canadensis, as a winter food item.
Hemlock Ravine Scientific and Natural Area (HRSNA) in northeastern Minnesota contains an unusual, isolated population of eastern hemlock; it is the largest population in this state and the only one showing substantial regeneration. Porcupines also use this area, and are protected within it; thus concern developed for the well-being of the hemlock population in HRSNA. This study was conducted during the winter and spring of 1988 to determine whether the hemlock population attracts large numbers of porcupines to this area, and if the porcupines at HRSNA seek out and preferentially use the hemlocks with greater frequency than predicted on the basis of relative abundance of hemlock in the stand.
Results indicated that the number of porcupines using HRSNA does not differ from porcupine densities found elsewhere in the north-central and northeastern portions of the range. Porcupines significantly selected the hemlock trees for all types of feeding (trunk-bark, limb-bark, and foliage feeding), but during the study season did not cause serious damage to this hemlock population. Thus, porcupine use of hemlock does not appear as intensive in HRSNA as in other areas where eastern hemlock is more numerous. Instead, the porcupines in HRSNA made heavy use of white cedar (Thuja occidentalis), white pine (Pinus strobus), and sugar maple (Acer saccharum), the latter two species to such an extent that survival was unlikely for certain of the trees fed upon.