Tallgrass prairies, a key feature of Iowa’s landscapes, are susceptible to woody encroachment. When undisturbed, this natural process makes it easy for woody species to invade open prairies and slowly transition them to forested areas. This study tests how herbivory and prairie diversity affect establishment of woody species in an experimental restored prairie within Ames, Iowa. We identified and measured all woody stems >0.5 m within four plots surrounded by fencing to exclude common herbivores (deer and voles) and in four plots without fencing. Each region contained areas with high and low diversity of prairie seedlings. Plots allowing herbivore access have fewer woody stems in both high and low diversity treatments than plots excluding herbivores, likely due to non-discriminant browsing by herbivores. Plots excluding herbivory had higher numbers of establishment in low diversity only and this was dominated by four species: Acer saccharinum, Cornus drummondii, Vitus riparia, and Pyrus calleryana. C. drummondii, V. riparia, and P. calleryana have fruiting seeds, which indicates that the more successful species tend to be frugivore dispersed. Overall, this study shows that areas with a lower diversity of non-woody prairie plants that exclude herbivory provide for higher establishment of invading woody seedlings.

Prairie areas free of established trees create an ideal habitat for seedlings of nearby adult trees, making it easy for woody species to invade Iowa’s natural prairies and slowly convert them to forested areas. This study aims to determine possible patterns of establishment of woody species in a restored prairie area within Ames, Iowa, focusing on the effects of herbivory and surrounding herbaceous biodiversity. Oakridge Prairie is sectioned into eight plots (four allowing herbivory, four preventing herbivory) and each block has areas of low and high grass/forb diversity. Heights, species, and locations within diversity and herbivory treatments were recorded for all seedlings above 0.5 m within this prairie. There is a significant relationship between herbivory treatments on seedling abundance and height, but not for herbaceous plant diversity treatments. Herbivores strongly limit woody encroachment. Dispersal mode affects dispersal distance, with animal dispersed seeds traveling farther from their nearest conspecific. Animals, likely birds, are dispersing seeds into prairies. Prairie managers should consider the effectiveness of herbivory on reducing woody encroachment into natural prairie areas.