Trade-offs between deer herbivory and nitrogen competition alter grassland forb composition

AbstractTwo of the major factors that control the composition of herbaceous plant communities are competition for limiting soil resources and herbivory. We present results from a 14-year full factorial experiment in a tallgrass prairie ecosystem that crossed nitrogen (N) addition with fencing to exclude white-tailed deer,Odocoileus virginianus, from half the plots. Deer presence was associated with only modest decreases in aboveground plant biomass (14% decrease; −45 ± 19 g m−2) with no interaction with N addition. N addition at 5.44 and 9.52 g N m−2 year−1led to increases in biomass. There were weak increases in species richness associated with deer presence, but only for no or low added N (1 and 2 g N m−2 year−1). However, the presence of deer greatly impacted the abundances of some of the dominant perennial forb species, but not the dominant grasses. Deer presence increased the abundance of the forbArtemisia ludovicianaby 34 ± 12 SE g m−2(94%) and decreased the forbSolidago rigidaby 32 ± 13 SE g m−2(79%). We suggest that these changes may have resulted from trade-offs in plant competitive ability for soil N versus resistance to deer herbivory. Field observations suggest deer act