The effect of White-tailed Deer herbivory on the leaf and root biomass of Thuja occidentalis in northern Michigan.

Abstract

The foraging habits of large populations of white-tailed deer (Odocoileus virginianus) can have a significant effect on Thuja occidentalis (northern white-cedar) ecosystems. Based on our hypothesis that deer browse affects root growth, we tested whether foliage and root densities differ between browsed and unbrowsed stands. We sampled from three sites, two mainland sites in contact with deer browse and one island site isolated from deer browse. Our results show that both foliage and root densities are significantly less in browsed areas of T. occidentalis. The average foliage density for the browsed site was found to be approximately thirty percent less than that for the unbrowsed site. Accordingly, the average root density for the browsed sites was also considerably less than that for the unbrowsed site, showing a decrease of approximately fifty percent. We speculate that the decreased photosynthetic area due to deer browse reduces nutrient uptake, thereby reducing root biomass. There was also a significant difference in regeneration patterns between browsed and unbrowsed T. occidentalis ecosystems. Contrary to what we expected, we found more woody groundcover in browsed areas. But, because we believe that the groundcover we found was not large enough for deer to forage on, there must be another variable that is responsible for the difference in woody groundcover between browsed and unbrowsed sites.