The effects of white-tailed deer herbivory on prairie community structure and function during restoration

Background/Question/Methods

The North American tallgrass prairie has been reduced by up to 99 percent of its historical extent. Restoration of this endangered ecosystem often aims to reinstate natural community structure and function. However, community composition of restored tallgrass prairies may not be controlled by the same mechanisms as extant contiguous prairie because abiotic and biotic factors operating during the initial years of restoration may select for or against the prevalence of re-introduced and volunteer species. White-tailed deer (Odocoileus virginianus) can be an abundant herbivore in tallgrass prairie and have been shown to have significant effects on prairie plant communities, particularly forbs. In the absence of cattle and bison, white-tailed deer can be the most prevalent ungulate in tallgrass prairie and there is little information about the role of this herbivore on the initial establishment of prairie communities.  We quantified community and ecosystem consequence of O. viginianus browsing during the establishment year of a prairie restoration. Deer exclosures were erected at the onset of a prairie restoration according to a randomized complete block design. Prairie was restored using a mix of native grasses and forbs at the Konza Prairie Biological Station.  To determine the effects of deer herbivory on initial composition and functioning of developing prairie, we measured deer browse, plant cover, diversity, and aboveground net primary production (ANPP) in plots assigned to control and deer exclosure treatments.

Results/Conclusions

The fences established at the onset of restoration effectively reduced browsing and led to differences in community composition and productivity between the deer-excluded and control treatments.  Approximately 11 percent of forb stems in control plots were browsed by deer (P=0.014).  Total ANPP was 49.7% higher within deer exclosures relative to the unfenced controls (P=0.05) resulting from release of non-planted, early successional forbs from herbivory. Percent cover of two forbs, Abutilion theophrasti (P<0.01) and Amaranthus rudis (P<0.01), was significantly higher in deer exclosure plots than controls but Shannon’s index of diversity was not different between treatments (P>0.05).  These results demonstrate that deer browsing has consequence for the functioning of developing prairie with implications for resource capture.  Longer-term monitoring of species composition will elucidate whether compositional and productivity differences in the initial year of restoration and under continued exclusion of deer will impact the community structure and function to an even greater extent as restoration proceeds.