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Submitted to: The Progressive Rancher
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 4/9/2016 Publication Date: 4/19/2016 Citation: Clements, D.D., Harmon, D.N., Young, J.A., Blank, R.R. 2016. Phenology of cheatgrass and associated exotic weeds. The Progressive Rancher. 16(5):8-9. Interpretive Summary: Cheatgrass, native to central Eurasia is an exotic, highly invasive annual grass that has dramatically changed the aspect and ecological functions of vast areas of formerly big sagebrush/bunchgrass and salt desert rangelands in the Intermountain west. Cheatgrass increases the chance of ignition, rate of spread and extends the season of wildfires. This reduces the interval between recurrent wildfires, eliminating most woody vegetation. Cheatgrass is such an efficient competitor for soil moisture it closes communities to the recruitment of seedlings of native perennial species, resulting in the truncation of succession and annual grass dominance. An area of rangeland that has been repeatedly burned and currently dominated by cheatgrass has an appearance of annual grass dominance even though numerous other exotic invasive weeds are present. We have documented more than 30 exotic invasive species that play a role in what are often thought of as cheatgrass “mono-cultures”. These range from other annual grasses such as medusahead which has been known to successionally replace cheatgrass on specific sites, to halogeton which can invade bare areas before Russian thistle. To get a better idea of what role many of these exotic invasive species play in these cheatgrass communities we set up an common garden study to compare the phenology of certain exotic invasive species (one native; tansy mustard) that occur in these cheatgrass communities as a means of assessing the nature of seral stage dominance and ecological amplitude of this invasion. Many exotic invasive weeds have overlapping phonologies with cheatgrass, bur buttercup completes its life cycle in the shortest amount of time and in the face of cheatgrass dominance, other species such as Russian thistle and halogeton emerge and set seed long after cheatgrass seed has matured. Understanding the array of exotic invasive weeds associated with cheatgrass can improve weed control practices for future rangeland rehabilitation/restoration practices. Technical Abstract: Cheatgrass (Bromus tectorum), is an exotic, highly invasive annual grass that has dramatically changed the aspect and ecological functions of vast areas of formerly big sagebrush/bunchgrass and salt desert rangelands in the Intermountain west. Cheatgrass increases the chance of ignition, rate of spread and extends the season of wildfires. This reduces the interval between recurrent wildfires, eliminating most woody vegetation. We have documented more than 30 exotic invasive species that play a role in what are often thought of as cheatgrass “mono-cultures”. These range from other annual grasses such as medusahead (Taeniatherum caput-medusa) which has been known to successionally replace cheatgrass on specific sites, to bur buttercup (Ranunculus testiculatus) which can complete its life cycle in the face of cheatgrass dominance. To get a better idea of what role many of these exotic invasive species play in these cheatgrass communities we set up an common garden study to compare the phenology of certain exotic invasive species (one native; tansy mustard) that occur in these cheatgrass communities as a means of assessing the nature of seral stage dominance and ecological amplitude of this invasion. Bare-ground species such as Barbwire Russian thistle (Salsola targus) and Halogeton (Halogeton glomeratus) are often problems on disturbed sites resulted in the emergence of Barbwire Russian thistle in early February, yet seed maturity was not until July. Halogeton did not emerge until mid-March and did not reach seed maturity until October. Both the exotic Tumble mustard (Sisymbrium altissimum) and the native tansy mustard (Descurania pinnata) have near simultaneous emergence in early November, very similar to that of cheatgrass, yet seed maturity was late-May to early-June. Salt desert shrub accession of cheatgrass on the other hand reached seed maturity in early-April while the upland accession of cheatgrass reached seed maturity in late-April to mid-May. Red brome (Bromus madritensis ssp. rubens) shares dominance with cheatgrass or is the dominant annual exotic grass in the warm deserts of the southern Great Basin. In the northern Great Basin it occurs in isolated small communities intermixed with cheatgrass. Red brome, used in this experiment, is similar to cheatgrass in emergence, but reached seed maturity by late-March to early-April. The array of exotic weed species that occur in either pre-successional, co-dominant or post-successional to cheatgrass help to assure the closing of the site to the recruitment of less competitive perennial species. The year-long overlapping of phenologies ensure complete utilization of limited resources, and the succession of these exotic annuals greatly complicate effective weed control practices. |
