Growth of Bear-Damaged Trees in a Mixed Plantation of Douglas-Fir and Red Alder

Incidence and effects of tree damage by black bear (Ursus americanus altifrontalis) in a 50-year-old, coast Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) plantation are described. Bears girdled or partially girdled 35 dominant or codominant Douglas-fir trees per acre, but only in that portion of the plantation that had been interplanted at age 4 with red alder (Alnus rubra Bong). No red alder were damaged. Bears damaged Douglas-fir in this stand on at least four occasions between 1929 (planting) and 1991. Fully girdled Douglas-fir (six per acre in 1976) died within 2 to 14 years. Of the 29 per acre partially girdled trees, 17 percent died in the 16 years of observation, compared to 9 percent of nondamaged trees. Crosssectional growth of surviving damaged trees exceeded that of matched, nondamaged trees by about 30 percent at three heights on the bole: 6 ft, 4.5 ft, and immediately above the damaged area. Death of six large Douglas-fir trees per acre reduced live stand volume of this species for about 6 years after bear damage until growth of the remaining trees compensated for the volume lost to mortality. Confirmation of the stimulating effects of bear damage on subsequent tree growth is needed at other locations.