Phenology of Cheatgrass and Associated Exotic Weeds Charlie D. Clements, Dan N. Harmon, James A. Young and Robert Blank
Rangeland Scientist, Great Basin Rangelands Research Unit, US Department of Agriculture, Agricultural Research Service, 920 Valley Road Reno, NV 89512 charlie.clements@ars.usda.gov Agricultural Research Science Technician, Rangeland Scientist (retired), and Soil Scientist US Department of Agriculture, Agricultural Research Service
C
heatgrass is an exotic, highly invasive annual grass that has dramatically perennial grasses, let alone cheatgrass. Bare-ground species such as Barbwire Russian changed the aspect and ecological functions of vast areas of formerly big thistle and Halogeton are often problems on disturbed sites. Barbwire Russian thistle sagebrush/bunchgrass and salt desert rangelands in the Intermountain emerges in early February, yet seed ripening was not until July. Halogeton did not west. Cheatgrass increases the chance of ignition, rate of spread and ex- emerge until mid-March and did not reach seed ripening until October. Halogeton tends the season of wildfires. This in turn reduces the interval between is known to produce seeds that have the ability to lay dormant in the soil for more recurrent wildfires, eliminating most woody vegetation. Cheatgrass is such an efficient than 10 years, so at around 100 seeds per plant produced, a very small percentage of competitor for soil moisture that it closes communities to the recruitment of seedlings dormant seeds can ensure the existence of viable seeds in the community for decade of native perennial species, resulting in the truncation of succession and annual grass after decade. Both the exotic Tumble mustard and the native Tansy mustard have dominance. Rangelands repeatedly burned and currently dominated by cheatgrass near simultaneous emergence in early November, very similar to that of cheatgrass, have an appearance of annual grass dominance, even though numerous other exotic yet seed ripening was late-May to early-June. The salt desert shrub accession of cheatinvasive weeds are present (Figure 1). As early as the 1930s, research by R. L. Piemeisel grass, on the other hand, reached seed ripening in early-April while the upland acon the Snake River Plains of Idaho, suggested that there was succession among exotic cession of cheatgrass reached seed ripening in late-April to mid-May. It is important invasive species and that the species that to understand that cheatgrass genermatured first “won the site”. We have ally germinates and emerges throughout documented more than 30 exotic invasive fall, winter, and spring months and on species that play a role in what are often certain events even summer months, considered cheatgrass “mono-cultures”. which results in collection of ripe cheatThese species range from other annual grass seed from April through August. grasses such as medusahead, which has Mustard species play an important been known to successionally replace role in increasing safe-site germination cheatgrass on specific sites, to halogeton for cheatgrass as these mustard species which can invade bare areas before Rusprovide excellent litter and increase the sian thistle. To get a better idea of the role germination of cheatgrass seeds. Red of many of these exotic invasive species brome shares dominance with cheatplay in cheatgrass communities, we set up grass or is the dominant annual exotic a common garden study to compare the grass in the warm deserts of the southphenology of certain exotic invasive speern Great Basin. In the northern Great cies (including one native; tansy mustard) Basin it occurs in isolated small comthat occur in cheatgrass communities as munities intermixed with cheatgrass. a means of assessing the nature of seral Red brome, used in this experiment, is stage dominance and ecological amplisimilar to cheatgrass in emergence, but tude of this invasion (Table 1). A total of reached seed ripening by late-March Figure 1. Numerous exotic invasive annual weeds 20 species were used, including two acto early-April. There are potentially hidden in a landscape dominated by cheatgrass. cessions of cheatgrass; upland and salt desmany several biennial and perennial exotic ert. The upland and salt desert cheatgrass accession are the same species but are known invasive weed species that have the ability to replace cheatgrass (e.g. knapweed). The to differ in phenology, morphology and physiological characteristics. Timing of: 1) exotic annual grass species, medusahead, is known to replace cheatgrass on certain emergence, 2) flowering, and 3) seed ripening was recorded weekly for the whole year soil types and during certain precipitation years. In other common garden studies, it (Figure 2). Initial germination in some species can happen quite quickly but is hard has been pointed out that the majority of medusahead accessions matured later than to record in this experimental design as we would have had to dig up seeds to count cheatgrass, although a few accessions did mature earlier than cheatgrass. In this study, percent and timing of seed germination. It is not uncommon to have seed species that medusahead emerged later than cheatgrass, mid-November and reached seed ripening germinate under the soil, yet not emerge for quite some time. Bur buttercup, an early in early to mid-April, similar to the upland cheatgrass accession. On given years, one season ephemeral species, germinated and emerged in less than a week in some cases can observe this slight difference where the two species co-exist as cheatgrass is in the and also reached seed ripening as early as late-March, which was by far the shortest red-stage while medusahead seed heads exhibit a bright green color. life span of any of the exotic annuals we tested (Figure 3). In fact, this species has the The array of exotic weed species that occur and exhibit germination, emergence, ability to germinate, emerge, grow and reach seed ripening in cheatgrass communities growth/competition and maturity in cheatgrass communities help to assure the closwhich are closed to the recruitment of native and desirable introduced species. Some ing of the site to the recruitment of less competitive perennial species. The year-long researchers and resource managers believe bur buttercup can out-compete cheatgrass overlapping of phenologies ensure complete utilization of limited resources, and the as well as emerging native species. We originally had a similar view, but while record- succession of these exotic annuals greatly complicate effective weed control practices. ing seedling emergence and recruitment on our hands and knees in one of our plant When conducting rehabilitation/restoration efforts, rangeland managers and property material testing plots in northern Nevada, we learned that bur buttercup is so early and owners must be aware of and include the array of other exotic invasive weeds that can so quick that it does not limit available resources for emergence and establishment of ultimately negatively impact the success rates of such efforts. 8 May-June 2016
The Progressive Rancher
www.progressiverancher.com