Abstract
American ginseng (Panax quinquefolius) is America’s premier wild-harvested, medicinal plant that inhabits the forest understory of eastern deciduous forests. Recent research revealed that birds, particularly wood thrushes (Hylocichla mustelina), disperse ginseng seeds by regurgitating viable seeds 15–37 min after consuming the berries. We carried out two studies to examine the potential effect of thrushes on spatial dispersion patterns of ginseng. First, to analyze how far wood thrushes could disperse seeds, two wood thrushes were outfitted with radio transmitters and tracked for multiple days. Second, for 28 natural populations of ginseng, we created a clustering index to quantify to what degree populations were structured into spatially separated units. To further detect spatial impacts of thrushes, we analyzed inter-cluster distances and the overall spread of ginseng populations. Over the time period in which wood thrushes retain ginseng in their guts, the seeds would be dispersed a mean distance of 15.2–21.7 m. The observed distances ranged from 0–96.6 m. These distances were comparable to the overall spread metric for ginseng populations with wood thrushes, which had increased spacing in comparison to those without wood thrushes. The mean dispersion index differed for populations with and without wood thrushes. It is imperative to understand the interaction between wood thrushes and ginseng to facilitate conservation, as both species are experiencing population declines. Dispersal of seeds by wood thrushes could play an important role in allowing species such as ginseng to respond to climate change, deer browse, overharvesting, and other environmental stresses.
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Acknowledgments
We thank Todd Katzner for his guidance in capturing and radio-tagging thrushes, as well as for help in obtaining all necessary permits. Thanks to Julie Mallon and Lydia Stiffler for their assistance with mist-netting and outfitting thrushes. We thank Dr. James Anderson and Dr. John Edwards for providing us with radio receivers and antennas. Forks of Cheat Forest landowners allowed us to carry out mist netting and radio tracking on their property. Finally, thanks to Amy Hruska, Jessica Turner, Jennifer Chandler, Quinn Doyle, and Anne Jarrell for help with collecting wood thrush presence data in the spring. Data concerning sub-population structuring of ginseng would not have been possible without contributions from numerous previous lab members. Funding for this research was provided by National Science Foundation grants DEB-0613611 and DEB-11118702 to J.B.M., the WVU Honor’s SURE Program, and the Henry W. Hurlbutt Memorial Fund from the WVU Department of Biology.
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Elza, M.C., Slover, C. & McGraw, J.B. Analysis of wood thrush (Hylocichla mustelina) movement patterns to explain the spatial structure of American ginseng (Panax quinquefolius) populations. Ecol Res 31, 195–201 (2016). https://doi.org/10.1007/s11284-015-1327-6
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DOI: https://doi.org/10.1007/s11284-015-1327-6