Growing white-tailed deer populations in some areas of the country are hurting and possibly killing hemlocks.
A research study published in the journal Ecology indicated high levels of nitrogen from deer urine excreted around hemlocks may be harming the trees and killing some of them. The deer return to the same areas each year for winter, using the hemlocks for shelter from brutal winds and cold. Smaller saplings and trees may be eaten, too, further harming the hemlocks’ reproductive process.
“Herbivores like deer interact with the ecosystem in two ways. One is by eating plants and the other is by excreting nutrients,” said Bryan Murray, an ecologist and doctoral student at Michigan Tech University, in a story on LiveScience.com. “Urine can be a really high nitrogen resource, and hemlock can be out-competed by other species in really high nitrogen environments.”
Apparently, the high-nitrogen output in the deer’s urine is just too much for the hemlocks. When the deer return each winter, and more of them pack into an area (and pee, of course), the resulting nitrogen buildup is more than the hemlocks can stand. They prefer soils with lower nitrogen.