Relationship between age, size, and reproduction in populations of American ginseng, Panax quinquefolius (Araliaceae), across a range of harvest pressures

Abstract

Size-selective harvest occurs not only in some animal species in the wild, but in some plant species. Panax quinquefolius, a perennial plant of eastern North America, is one such species. As harvest of this species is fatal, there is potential for evolutionary change if selected traits are heritable. In this study, we compared traits potentially affected by selection among 12 populations with different harvest pressures. We used the recovery pattern of an experimentally harvested population to develop an index of harvest pressure: the proportion of seedlings and juveniles. Age was related to leaf area, sympodium (stem) height, and reproduction in populations across a range of harvest indices (HI = 0.4122–0.9583). We detected variation among populations with different harvest indices in the age-leaf area relationship in 2006. A 10-y-old plant would have 30% less leaf area in a population with high harvest pressure (HI = 0.9) than in a population with low harvest pressure (HI = 0.4). Similar results were observed with sympodium height in 2005 and 2006. Reproductive plants in populations with higher harvest indices had reduced seed set, likely due to Allee effects. A separate, related study showed that leaf area differences were maintained among plants from 8 populations 4 to 5 y after transplantation to a common environment. Reduced growth rates in populations with higher harvest pressure may be the outcome of appearance-mediated selection.