Sunday, July 13, 2014

The Evil Disappears along with Canada Barberry?

Berberis canadensis showing the bristly leaf margins
Canada Barberry (Berberis canadensis) and the non-native Common Barberry (Berberis vulgaris) are very similar in appearance. According to Weakley's flora the most obvious difference between the two is the number of bristles on the leaf margins (the image on the right shows the relatively sparser bristles on B. canadensis).

Distinguishing these two may be especially relevant given that Common Barberry was apparently heavily naturalized in the eastern US by the early 1900's. In a 1920 survey, over 1,600,000 "escaped bushes" were found in the north-central states (1). The status of B. vulgaris in NC is unclear although it has been documented here (8)

Although Common Barberry was introduced for various beneficial uses, it had also long been considered a potential threat to agriculture for well over a century; "One extraordinary fact is that the barberry bush will produce smut, or something very similar to it, in all corn growing within a considerable distance of soon as the barberry has been thoroughly extirpated, the evil disappears" (2)  

This "extraordinary fact" ended up contributing to what has been considered the largest and most intensive non-native plant control effort in US history (3).  By 1918, USDA and numerous states were implementing broad reaching programs to eradicate Barberry in an attempt to protect wheat and other cereal crops from infestation by black wheat rust, the spores of which were determined to be spread especially by Common Barberry (Berberis vulgaris). At least one botanist posed objections to the wholesale slaughter of the Common Barberry, but never mentioned the potential loss of, or confusion with, Canada Barberry (4) .

Perhaps, this lack of concern was initially based on statements by USDA that native barberries...."seem to be of very little or no importance in spreading rust" (5). However, by 1921, it had been determined that "only one species of native barberry (Berberis canadensis) rusts abundantly enough to be dangerous" (1).  It is unclear how aggressively, if at all, Canada Barberry was pursued for eradication, but given the similarity of appearance to Common Barberry and the wide range of citizens involved in control programs, it is likely that Canada Barberry would have been destroyed if encountered.

Control efforts focused on the north-central states (1) and continued through at least 1981 although it was believed that 98% of the infected areas had been eradicated nearly a decade prior to that (6). It has been estimated that over 500 million Berberis were removed by cooperative eradication programs (3).

The current rarity of Berberis canadensis in the northern parts of the known natural range (PA, VA, IN, IL, MO) could well have been facilitated by Wheat Rust-associated eradication programs. However, such programs apparently did not extend south of Virginia (6); wheat rust spores in the south (Missouri and Kentucky southward) lose viability (1) and therefore, eradication programs were less needed. Although at least one southern state (7) still lists eradication programs as a threat, I have found no reliable evidence for barberry eradication in NC or southward, and am not convinced it was a significant factor in creating rarity in NC, SC, GA or other southern states.

Berberis canadensis with dangling inflorescences

Trifurcate thorns are typical of B. canadensis
(but also B. vulgaris)
It is unclear why Canada Barberry is so uncommon in NC and places southward. Possible explanations are its tendency to associate with higher pH soils (rare in and of themselves) and relatively open sites (also rare and becoming rare).  A couple of years ago I found a large population (which Harry LeGrand later estimated to be NC's largest) in the Uwharrie region of NC, along an open roadside with a host of prairie associates; the site has since been destroyed by road construction. I know of one apparently thriving and protected population which is the source of the images here. More commonly, Japanese Barberry can be found naturalizing in NC.  
Japanese Barberry (Berberis thunbergii);
this specimen apparently planted at the Linville Falls trailhead
Today, in North Carolina's "natural areas" we may need to reconsider the message on the sign below.
(1) Annual Reports of the Department of Agriculture , 1920
(2) The Principles of Agriculture, Thaer 1844, 2 volumes, London
(4) American Botanist, 1918 (William Clute essay)

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