Plant phenology, seed dispersal, and eastern red cedar range expansion: It's all about timing!

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Kaitlin Shvach, Biological Sciences, Kent State University, Kent, OH, Mark W. Kershner and Oscar J. Rocha, Department of Biological Sciences, Kent State University, Kent, OH

Background/Question/Methods
Eastern red cedar (Juniperus virginiana; ERC) is native to eastern North America, but is expanding into grassland and prairie ecosystems of the midwestern United States. ERC produces small light-green cones during spring that mature over the next 6-8 months. As cones mature, they increase in size and become deep-purple, indicating changes in seed viability and nutrient content. Ultimately, these changes act as a visual signal to attract foraging birds and mammals, driving ERC range expansion through seed dispersal in late-fall and winter when other food sources are scarce. After fecal deposition, these seeds likely germinate, allowing colonization of new sites. Thus, successful seed dispersal depends upon temporal overlap between foraging and viable seeds. Foragers differ in presence and feeding, with resident birds and mammals present year-round, nomadic foragers occasionally present as they track food availability, and migratory species present only during spring/fall migrations. To understand these interactions, we characterized ERC cone phenology and seed availability/viability monthly while also documenting foraging by birds and mammals using wildlife cameras/microphones. We seek to define the relationship between plant phenology and animal-mediated seed dispersal to understand ERC range expansion.
Results/Conclusions
This project focuses on the timing of animal foraging and cone phenology to best estimate potential seed dispersal. For successful dispersal, cones containing mature and viable seeds must match the presence of their disperser, making temporal overlap critical.
In August, 60% of cones had shifted from green to purple, completing the maturation process, signaling to the foragers that cones are ready to be consumed. This change coincides with the completion of seed development, and high nutrient content for dispersal. All feeding groups have the potential to disperse viable seeds, particularly resident feeders. Resident species forage for the entirety of the time that the cones are present (May-March). Migratory species feed during migratory periods (August-November) and (January-April). Nomadic species move as resources change, staying within a similar latitude, often feeding November to February.
We documented cone foraging by many species and observed primarily white-tailed deer, American robin, and European Starling. Understanding the dispersal process can allow us to mitigate the range expansion of this species into grassland ecosystems and prevent its spread into new areas, avoiding the establishment of monoculture stands and the extinction of native herbaceous plants. We discuss the causes and consequences of the mismatch between the timing of animal foraging and cone phenology on the encroaching behavior of ERC.