F-501816 

 Figure 1. — This 6-inch sugar maple shows partial 

 or complete girdling by porcupines each year 

 for 3 years. 



percent within the previous year. A census of 

 the quarter section under study showed that 

 9 to 12 animals were present and probably 

 had been present during the previous winter. 

 The data suggest that, in any given year, a 

 population of 40 to 50 animals per square 

 mile would affect in some way about 5 percent 

 of the trees represented in a selectively mark- 

 ed commercial cutting. 



Five percent is a maximum value for the 

 entire stand, as indicated by the bias in mark- 

 ing toward trees previously damaged and 

 most susceptible. Trees left standing would 

 show a somewhat lower incidence of feeding 

 damage. 



Certain trees showed a disproportionate 

 amount of activity. Apparently, after an ani- 

 mal discovers a suitable tree, he returns to 

 it year after year and may be joined by other 

 animals. 



Activity was concentrated in relatively 

 limited portions of the area, primarily in the 

 vicinity of hemlock. Elm and hemlock show 

 almost twice as much use in relation to avail- 



ability of stems as do sugar maple and yellow 

 birch: basswood is intermediate in use. Dam- 

 age to elm is light since feeding is normally 

 restricted to small twigs, while the bark is 

 stripped on other species. 



Current silvicultural practices discrimi- 

 nate against hemlock. This, combined with 

 regeneration failures and deer browsing, is 

 causing the gradual disappearance of hemlock 

 from many stands. The change in composition 

 may lower the carrying capacity for porcu- 

 pine. Whether the final result will be a drop 

 in the population or (more likely) less con- 

 centrated feeding activity and increased use 

 of valuable timber species by porcupine is 

 still in doubt. The presence of den sites is al- 

 so an important factor in maintenance of por- 

 cupine populations. 



Study of a hardwood logging operation 

 near Ada Lake in Wisconsin revealed some- 

 what greater porcupine activity than at Gold- 

 en Lake. Again, 58 percent of the total trees 

 cut had been gnawed, but feeding activity 

 was more intense; during the previous 2 

 years, it was almost four times as great (44 

 percent) as it had been at Golden Lake. Kills 

 during control hunts indicated a porcupine 

 population in the Ada Lake stand of approx- 

 imately 50 to 75 animals per square mile, a 

 considerably higher population than at Gold- 

 en Lake. Thus, feeding damage appears readi- 

 ly related to population size. 



Based on percentage of trees gnawed, de- 

 gree of injury, and currentness of feeding, 

 the activity in the Ada Lake stand was 27 

 percent greater than that at Golden Lake. 

 This compares favorably with the difference 

 (25 percent) in estimated animal popula- 

 tions. 



Results of this study suggest that knowl- 

 edge of the currentness and intensity of feed- 

 ing and percentage of the trees gnawed in 

 a stand may provide a means of estimating 

 porcupine populations in the northern hard- 

 wood forest type. Population and behavior 

 data will help forest managers to make intel- 

 ligent decisions on the need for and the type 

 of porcupine control measures to be exer- 

 cised. 



ROBERT'BRANDER, Biologist 



University of Michigan 

 FOREST W. STEARNS, Research Forester 

 ( General ) 



Lake States Forest Experiment Station 



July 1963 



