Cheatgrass: Fire and Forage on the Range

Chapter 5. Seral Continuum: The First Step

Does the plant community concept of ecology as taught by John Weaver and Frederic Clements apply to introduced weeds such as cheatgrass? The answer is a highly qualified “yes and no.” Succession does occur among plant communities dominated by exotic annual species on temperate desert rangelands. In fact, we will show in this chapter that a host of exotic species occupy the same site in succession. Each succeeding assemblage of species modifies the potential of the site, paving the way for the next step in succession . The environmental factors modified by each assemblage of plants are most often seedbed characteristics, because the seedbed is the selective filter that controls the species composition of the next successional stage. The radical difference between the secondary successional process that actually occurs in Great Basin rangelands and the one Clements envisioned is that succession does not proceed through a series of stages, increasingly dominated by perennials, until a stable climax of native species is in equilibrium with the potential of the site. Cheatgrass truncates succession and becomes dominant for prolonged periods. The slightest disturbance is sufficient to perpetuate cheatgrass dominance. Classic secondary plant succession begins with bare ground, just as it did in Weaver’s and Clements’s abandoned vegetable garden. The first exotic species introduced into the degraded rangelands of the Intermountain Area chapter 5 Seral Continuum The First Step 66 turned out to be the primary successional species in the seral continuum that ends in cheatgrass dominance. This species is Russian thistle. Russian thistle is a weed that has been associated with agriculture for so long that its original range is lost in antiquity.1 It came out of the steppes of Asiatic Russia , where cereal production covered extensive areas. It is one of the few species whose original introduction into North America and subsequent spread are fairly certainly known. The fact that this history was recorded is a tribute to the devastating influence the weed has had on American agriculture, especially on the northern Great Plains. Late in the nineteenth century, the U.S. secretary of agriculture received multiple complaints from the northern Great Plains about a terrible weed that was destroying wheat production . S. W. Narregang, president of the Dakota Irrigation Company, wrote on October 28, 1891: I send you here a fair specimen of the Russian thistle. I would say that we first saw it three years ago. Since that time, it has steadily increased, until at present the greater portion of South Dakota east of the Missouri River is infested with the thistle, particularly the strip of counties extending from Eureka, Campbell southeasterly to Sioux Falls, which is covered thickly with this weed. This obnoxious weed has become so formidable in some portions of the state, notably in Scotland, South Dakota, where the Russian[s] formerly settled, that many farmers are driven from their homes on account of it. A man who was there some time ago states that farmers were leaving their land by the dozens simply because of the evil weed.2 As complaints mounted, the secretary dispatched Assistant Botanist Lyster Moxie Dewey to investigate the biological nature of the plant and find a means of eradication. Dewey proved to be an astute detective as well as a botanist. He discovered that Russian thistle was first introduced on a farm in Bonhomme County, South Dakota, about 1877. A few seeds of the thistle were mixed with flax seed imported from Europe.3 One aspect of the introduction had ugly social undertones; many believed that the weed was deliberately introduced by Russian Mennonite emigrants in revenge for perceived social injustices. Dewey went to considerable lengths to dispel that theory. On the botanical side, Dewey reported that Russian thistle was an annual that completed its life cycle in one year. The most objectionable thing about s e r a l c o n t i n u u m : t h e f i r s t s t e p 67 the plant was its sharp, spinelike leaves, which could lacerate the legs of horses running in pastures. Some farmers bound their horses’ legs with leather to protect them.4 The most remarkable part of the life cycle of Russian thistle occurred in the fall. As the November winds blew across frozen fields, the plants snapped off at the soil surface and tumbled with the wind, racing across the fenceless, treeless plains, scattering seeds with...