Ginseng Life Cycle
Ginseng plants, like humans, go through different developmental stages. Ginseng begins life as a seed, remaining in the soil 18 months prior to germination. A recently germinated ginseng has 1 leaf with 3 leaflets. These fragile plants are more susceptible to the 'elements' than they are at any other life stage; a drought or a disease outbreak may kill off all but the strongest juvenile plants. Ginseng may remain a 1 leaf plant for several years as it accumulates enough energy to grow into a 2 leaf, adolescent ginseng. Two leaf ginseng may develop flowers and seeds, but reproduction is intermittent and low. Ginseng remains in this 2 leaf stage for another 3-5 years before developing into a large adult plant (typically with 3 leaves), which may in old age eventually have 4, or rarely 5 leaves. These adult plants are hardy, and contribute the majority of seeds produced in a population of ginseng. It is these large adult plants that are removed from the population during a harvest event.
Defining these life stages is important for demographic research. As you can see, plants at different life stages vary in terms of fecundity and mortality. In order to accurately model population growth in American ginseng, life stages that capture these demographic characteristics must be created. This type of classification is referred to as stage-based classification, because we use the size or stage of the plant, not the age, to assign ginseng to groups. In our actual demographic model of ginseng population growth we use a more detailed version of the life cycle described above. In order to capture differences in reproduction of larger plants, we divide adult plants into two groups based on leaf area. Finally, we incorporate an age-based model of the progression of seeds through the seed bank. Seeds can remain viable in the soil for up to four years. As seeds age, however, the likelihood of that seed germinating decreases. Hence, we incorporate this aspect of ginseng biology into our demographic model of population growth, by adding information on seed bank dynamics.
The analogy with human development only goes so far. In fact, unlike humans, ginseng plants can revert to earlier stages, reflecting a 'plastic' response to the environment. After being browsed by a deer, or experiencing a bad drought, a given plant often comes back the next year reduced in size, lower in reproductive output, and potentially more likely to die.