Rodent Damage to Fertilized Pacific Silver Fir in Western Washington

Abstract

Terminal shoots and buds of Pacific silver fir (Abies amabilis [Doug.] Forbes) which had responded to nitrogen fertilization were significantly damaged by rodents during the winter of 1960—61 in contrast to adjacent unfertilized trees. Small mammal trapping studies in the area the following summer showed no general rodent population increase. We believe that changes in the feeding behavior of samll rodents did occur as a result of the fertilizer treatment and a 20% increase in nitrogen and protein content of silver fir vegetative tissue. We also postulate that Clethrionomys was the rodent responsible for the selective use.