Deer browsing and population viability of a forest understory plant.

American ginseng is the premier medicinal plant harvested from the wild in the United States. In this study, seven populations of ginseng plants were censused every 3 weeks during the growing season over 5 years to monitor deer browse and harvest and to project population growth and viability. The minimum viable population size was approximately 800 plants, a value greater than that of all populations currently being monitored. When simulated deer browsing rates were reduced 50% or more, population viability rose sharply. Without more effective deer population control, ginseng and many other valuable understory herbs are likely to become extinct in the coming century.