Are Black Cohosh Harvests Sustainable?

New tool helps managers estimate black cohosh in forest stands

Volunteer citizen scientist harvests black cohosh root to measure above and below ground biomass for development of a model to predict root biomass. Photo by U.S. Forest Service.
Volunteer citizen scientist harvests black cohosh root to measure above- and below-ground biomass for development of a model to predict root biomass. Photo by U.S. Forest Service.

In Southern Appalachians forests, harvests of non-timber forest products—plants used for culinary, floral, medicinal and other purposes—just keep increasing. Though overharvesting seems to be a major cause for population declines in plants such as American ginseng, black cohosh, and other medicinal plants, forest managers have lacked methods that would allow them to measure the extent of plant populations and to accurately assess the effects of harvest.

In an article published in the April issue of Forest Ecology and Management, U.S. Forest Service research Jim Chamberlain and university co-authors present a tool that estimates the below-ground biomass of black cohosh (Actaea racemosa) based on measurements of above-ground vegetation.

“The model we developed provides a practical, efficient, and simple approach to guide forest managers in the sustainable use of black cohosh,” says Chamberlain. “It should also serve as a template for developing inventory and management plans for other non-timber forest products.”

Black cohosh, a forest herb native to the Appalachian Mountains region, spreads by sending out rhizomes, underground stems that spread horizontally and produce roots and shoots. Before European settlement, Native Americans harvested the rhizomes of black cohosh to treat female conditions and a variety of other ailments. The use of the herb expanded when European settlers adopted Native American treatments and started using it to treat smallpox and cholera.

“Today, rhizomes of black cohosh are harvested primarily to support demand for herbal treatments of menopausal symptoms, with over 2 million pounds harvested from the forests of the eastern United States from 1997 to 2005 alone,” says Chamberlain. “The American Herbal Product Association estimates that more black cohosh was harvested during that period than any other herb it tracks, with little effort to manage the plant as a natural resource.”

Though foresters have a long history of developing accurate measurement of timber and tree growth, there are few such measures for black cohosh and other non-timber forest products. “No methods have existed to estimate the extent of rhizomes below the ground based on above-ground vegetation,” says Chamberlain. “Because of this there hasn’t been a way to find out how much rhizome biomass accrues or decreases in a year, or how much volume is available for harvest in a given year.”

Black cohosh rhizomes. Photo by National Park Service.
Black cohosh rhizomes. Photo by National Park Service.

The researchers set out to develop their model using data from long-term study sites established in 2005 in Virginia to examine sustainable harvest. In 2011, they extended the study to three more sites in Virginia to validate the accuracy of the model developed from the 2005 sites. In the course of the study, the researchers dug up and measured 1164 rhizomes and associated vegetation to make the calculations for the model and to validate its accuracy.

Though wide variability in plant size and the tight interwoven nature of the rhizomes themselves precludes using the model to predict the below-ground mass for individual plants, the researchers found that the model gives a good assessment of the volume of black cohosh rhizomes available for harvest at the stand level.

‘To date, there’s been no effective way to predict the total abundance of below-ground plant material in natural populations without destructive harvesting,” says Chamberlain. “The ability to make stand-level predictions will be very useful to managers who are trying to determine sustainable harvest levels of black cohosh. Though focused on black cohosh, the protocols and model we developed is probably adaptable to other species harvested for their below-ground rhizomes such as goldenseal and wild yam.”

Working with colleagues at Radford University, Chamberlain is expanding the study to include blue cohosh, bloodroot and wild yam, with the goal of establishing harvest and inventory protocols.

Access the full text of the article including the model.

Chamberlains annotated bibliography on black cohosh.

For more information, email Jim Chamberlain at jchamberlain@fs.fed.us.

Watch an SRS video made at the beginning of Jim Chamberlain’s black cohosh sustainability study:

[youtube_sc url=http://youtu.be/WSvgI1gW5g8 rel=0 fs=1 autohide=1 modestbranding=1]

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