Analysis of wood thrush (Hylocichla mustelina) movement patterns to explain the spatial structure of American ginseng (Panax quinquefolius) populations

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.

Demographic stimulation of the obligate understorey herb,Panax quinquefoliusL., in response to natural forest canopy disturbances

“…Additionally, although fertility of surviving individuals increased directly following the ice storm, many of the berries that were produced desiccated prior to dispersal (J.L. Chandler and J.B. McGraw, personal observation), limiting both seed viability and the potential for long‐distance dispersal via frugivorous birds (Hruska, Souther & McGraw ; Elza, Slover & McGraw ). Further, the above‐ground portion of the plants at the WKY populations began senescing earlier in the fall than plants in many other routinely censused populations that were not included in this study (J.L.…”

Evolution of the Araliaceae family involved rapid diversification of the Asian Palmate group and Hydrocotyle specific mutational pressure

“…This implies that natural dispersal may have been difficult owing to geographical and climatic isolation and that some mediator was needed for migration. It has previously been suggested that birds or small mammals might have carried Panax species into North America [76][77][78] . Furthermore, during the Early Pleistocene, the steppe mammoth (Mammuthus trogontherii), a trunked mammal, was estimated to have migrated from Eurasia to North America around 1.3-1.5 Ma 79 , coinciding with the split between P. ginseng and P. quinquefolius in this study (Figs.…”

“…4) [72][73][74] , and the second stage was migration of P. quinquefolius (node 106 in Fig. 4), which occurred during recurrent glaciations and was likely mediated by animals, including birds and small mammals 33,35,[76][77][78] , as well as trunked mammals.…”

Ecological Effects of Forest Canopy Disturbance on the Understory Plant, American Ginseng (Panax quinquefolius L.)

“…While population growth rate was stimulated by the ice storm, leaves of plants that remained were noticeably thickened and showed signs of photooxidation (Chandler and McGraw, personal observations). Additionally, although fertility of surviving individuals increased directly following the ice storm, many of the berries that were produced desiccated prior to dispersal (Chandler and McGraw, personal observation), limiting both seed viability and the potential for long-distance dispersal via frugivorous birds Elza, Slover & McGraw 2015). Further, the aboveground portion of the plants at the WKY populations began senescing earlier in the fall than plants in many other routinely censused populations that were not included in this study (Chandler and McGraw, personal observation), a pattern also observed in Panax ginseng grown under high irradiance (Parmenter and Littlejohn 2000).…”