Threats to Wild American Ginseng
Overbrowse by Whitetail Deer
White-tailed deer are currently the most abundant ungulate in the eastern deciduous forest. Due to loss of top predators, creation of ideal edge habitat, and management to maximize hunting success, the deer herd is near historic highs across much of its range. The most visible effect of single-purpose management for people is that overpopulation by deer increases collisions with cars, increases car insurance rates, and even more seriously, can cause injury or death of drivers. Deer also browse landscaping, making it impossible to grow some species of plants and requiring vegetable gardeners to vigorously fence their plots.
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Image right: White tailed deer on study trail cam. Credit: McGraw Labs, WVU
Less visible, but still serious, are the many ways that deer impact natural plant populations, including ginseng. Deer do not particularly prefer ginseng over other plants, but deer will eat ginseng if they are in the same area (Fig. 1). Scientific research has demonstrated that the effect of over browse by white-tailed deer is overwhelmingly negative and can quickly lead to a depauperate understory. When deer eat reproductive plants, they destroy the seeds (1) . With repeated browsing, plants shrink, have lower seed production and eventually die (2,3,4) . At current deer population densities browsing significantly increases local extinction risk, sometimes beyond even that of poor harvest practices
4 . Indeed, a recent study found that while a group of plants located safely atop a large boulder refugia in a heavily deer- browsed site exhibited increases in population size over time, the population
size of plants exposed to deer browse off of the rock at the same site decreased by 4.5% per year (5) . Moreover, when compared to the protected plants on the rock refugia, a large percentage of the plants exposed to over browse remained in a stunted, juvenile state (5). As with management of most of our natural resources, when one element gets out of balance, the rest of the system suffers.
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Notice below, that the leaves of the 4-prong American ginseng in the top two images are eaten, and are no longer visible in the bottom two images, which were captured three minutes later.
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Figure 1) Images of a white-tailed deer browsing the leaves of a mature, adult American ginseng plant are caught on a trail camera.
Deer and ginseng sequence from study trail cam. Credit: McGraw Labs, WVU
(1) Furedi and McGraw 2004. White-tailed deer: Dispersers or predators of American ginseng seeds?
(2) Furedi 2004.
(3) McGraw and Furedi 2005. Deer browsing and population viability of a forest understory plant.
(4) Farrington et al. 2008.
(5) McGraw and Chandler 2018. Demographic hallmarks of an overbrowsed population state in American ginseng.
What can you do about overbrowse by deer?
(1) If you are a landowner, encourage ethical deer hunting to reduce population sizes (and encourage your neighbors to do likewise).
(2) Encourage holistic ecosystem management for the good of all biodiversity.
(3) While this one is more controversial, in areas where hunting pressure cannot be raised to sufficient levels, natural controls may need to be introduced. Consider supporting reintroduction of top predators and/or protecting those already in the forest to help control deer populations.