A 'barker' was a person who stripped bark from trees to supply bark mills.
Tanbark around the world 
In some areas of the United States, such as central Pennsylvania and northern California, tanbark is often called "mulch," even by manufacturers and distributors. In these areas, the word "mulch" may refer to peat moss or to very fine tanbark. In California, Lithocarpus densiflorus (commonly known as the tanoak or tanbark-oak) was used. In New York, on the slopes of Mount Tremper, hemlock bark was a major source of tanbark during the 19th century.
In Africa and Australia, acacia (called "wattle") bark is used by tanners.
Oak bark 
In Europe, oak is a common source of tanbark. Quercitannic acid is the chief constituent found in oak barks. The bark is taken from young branches and twigs in oak coppices and can be up to 4 mm thick; it is grayish brown on the outside and brownish red on the inner surface.
See also 
- Chapter 8 - Tannins: Major Sources, Properties and Applications. Antonio Pizzi, Monomers, Polymers and Composites from Renewable Resources 2008, Pages 179-199, doi:10.1016/B978-0-08-045316-3.00008-9
- Flavan and procyanidin glycosides from the bark of blackjack oak. Young-soo Bae, Johann F.W. Burger, Jan P. Steynberg, Daneel Ferreira and Richard W. Hemingway, Phytochemistry, Volume 35, Issue 2, January 1994, Pages 473-478, doi:10.1016/S0031-9422(00)94785-X
- Quercus on www.henriettesherbal.com
- Oak on www.online-health-care.com
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