Effects of Elk Herbivory
The Project: Use elk exclosures and several nitrogen measurements to determine soil fertility and nitrogen ﬂuxes.Schoenecker utilized three elk exclosures set up by the park in 1963 as well as 12 that her team set up in 1994 to determine the eﬀ ect of elk herbivory on plant production and soil fertility. These two diﬀerent exclosure installment years gave researchers the ability to look at elk eﬀ ects after periods of four and 35 years. Nutrient sampling was conducted outside of the fences where the elk were allowed to graze and inside the exclosure fences where elk were prohibited from grazing, allowing researchers to deduce the eﬀ ect of elk herbivory on vegetation and soil fertility. Researchers determined above-ground and below-ground nitrogen pools through analysis of nitrogen concentrations in vegetation clippings and soils/roots, respectively. Additionally the investigators measured leaf litter nitrogen deposition, soil nitrogen available to plants for uptake, and amount of nitrogen taken in by elk during herbaceous consumption to establish the eﬀ ects of elk on nitrogen ﬂuxes. The team also established the amount of nitrogen deposited by elk via fecal and urinary waste by observing elk for 24-hour periods in order to determine potential rates of nitrogen transfer by elk among diﬀ erent vegetation types.
The Results: Elk negatively impact willow and aspen by causing a net loss of nitrogen, which reduces plant productivity and may alter the types of plants that can survive.Findings indicate that in willow and aspen vegetation types, elk herbivory had a signiﬁ cant negative eﬀ ect on nitrogen dynamics by causing a net transfer and loss of nitrogen from willow and aspen communities. For instance, elk herbivory signiﬁ cantly reduced willow shrub size, plant biomass, above-ground nitrogen pools, litter deposition, and the amount of nitrogen willows produce annually. Nitrogen losses from willow and aspen communities from elk herbivory were not compensated for by inputs of nitrogen from elk defecation and urination.
Due to lowered nitrogen availability the researchers saw evidence of substantial reductions in plant productivity and growth rates in willow and likely aspen communities. In light of their results, the researchers recommend management of elk numbers and their subsequent eﬀ ects upon park vegetation communities by reducing the elk population or by eliminating over-concentrations of elk.
This summary is based on published, peer-reviewed and/or unpublished reports available at the time of writing. It is not intended as a statement of park policy or as a deﬁ nitive account of research results. For more information on the park’s research program, see www.nps.gov/romo
Updated: January 2008