As you can tell by going through archived blogs on this site, medusahead (Taeniatherum caput-medusae) is an extremely popular grass. Well, an infamous one, perhaps. I am fairly certain that none of us actually like it. In this blog I will add to the plethora of medusahead posts; but first, a public service announcement.
On May 2, 2017, there will be a Medusahead Management Workshop at Lindcove REC, in Exeter. Online registration is available at ucanr.edu/medusahead. This workshop aims to inform attendees about medusahead biology, its economic impact on cattle operations, and a variety of tools available to ranchers and rangeland managers to tackle medusahead. Medusahead is already found throughout California's Central Valley rangelands. In my counties of Fresno and Madera, medusahead does not yet have the notoriety that yellow starthistle does, but ranchers are noticing it. With luck, we can raise their awareness and encourage action before it becomes the recurring problem that starthistle poses.
Now back to the grass. Let's talk about how medusahead compares to another invasive annual grass on rangelands. The two species have similar invasion histories and ecological attributes. This similar species is downy brome (Bromus tectorum, cheatgrass), which I studied for my Master's thesis in Montana and later encountered in northwestern Utah rangelands. In contrast to the southern San Joaquin Valley's annual grasslands/oak woodlands, Montana and Utah have perennial grasslands and shrublands, and most precipitation comes in late spring and early summer. As a result, the perennial systems interact with annual grass weeds differently than our annual grasslands do - usually.
Downy Brome inflorescence Medusahead inflorescence
Patch of Downy Brome Patch of Medusahead
Background on Downy Brome – in California and Elsewhere
Downy brome has not always been considered “bad”, even though most current discussion could convince you otherwise. Decades ago, many Great Basin cattle owners appreciated downy brome as a source of nutritious forage early in spring when the dominant landscape included unpalatable shrubs, dormant perennial grasses and large patches of naturally bare soil between them. Downy brome is quite palatable and nutritious for the first few weeks after snowmelt, or after fall germination in areas without winter snowpack. Even today, some ranchers still take advantage of downy brome when it is young and green. Downy brome seeds have also become an important part of some wild granivore diets (Young 1992). However, most land managers are not willing to overlook the increased chance of wildfire and the variability in annual downy brome forage production (Schmelzer et al. 2014), for the short-lived benefit to their livestock. In many areas, downy brome also displaces better forages, negating any benefit to grazers in those ecosystems.
Fortunately, downy brome is not a major concern on rangelands in the San Joaquin Valley. Even when it enters our systems, downy brome does not have the same opportunities to establish that it has found in perennial grass and shrub systems elsewhere. Downy brome follows more or less the same winter annual life cycle as the dominant forage species in California annual grasslands. It does not pose any greater risk of wildfire than the existing annual grasses here. Compared to the landscape in the Great Basin and Montana, there is no vacancy on these grasslands for downy brome to exploit. In fact, several other bromes are much more common on our rangelands, including ripgut brome (Bromus diandrus) and red brome (B. rubens). Here, downy brome is just one of many grasses in the mix – and the others have been here longer, with larger seed banks and many more decades of adaptation to local microclimates.
Comparison to Medusahead
Medusahead has invaded many of the same places downy brome is now found, including the Great Basin and other parts of the Intermountain West, Montana, and California. Ecologically speaking, medusahead does provide soil cover and stabilization, making it marginally better for soil erosion prevention than bare soil. Otherwise, medusahead has most of the same negative qualities of downy brome, and worse. Medusahead seeds do not appear to be palatable to granivores (Young 1992). Its thatch, as has been previously discussed on this blog, is nearly impenetrable to seedlings of other species, in part due to its slow degradation, a side effect of high silica content (Harris 1965; Kyser et al. 2014; Hamilton et al. 2015). Downy brome litter, while it can form a continuous source of fine fuels, does not result in the same restriction of other plants that is imposed by the persistent medusahead thatch. Whether these differences have caused the different invasion ability of medusahead as compared to downy brome, I cannot say. However, some combination of characteristics clearly differentiates the two species on an ecological or “behavioral” level, because medusahead is a problem in both the Great Basin type systems and our own annual grasslands.
Medusahead can remain green later than other annual grass species, including downy brome, especially where some soil moisture is still available later in the season (Young 1992). Nevertheless, the combination of long awns and silica deposits makes medusahead both less palatable and likely more difficult to digest than downy brome (Hamilton et al. 2015). These qualities reduce the potential of prescribed grazing to be an effective tool to tackle medusahead, relative to downy brome, although it still can be done (Kyser et al. 2014). Fortunately, grazing is only one of many tools to control medusahead that have been and continue to be studied by UC ANR scientists and others, and I am optimistic that we will find ways to limit the impact of medusahead on rangelands and livestock production in California.
Ultimately, while downy brome has failed to become invasive and abundant on San Joaquin Valley rangelands, medusahead appears to be capable of invading and dominating our annual grasslands. As such, we'll leave the concern about downy brome to other areas, and continue to focus on medusahead here at home.
References:
Hamilton, T., E. A. Burritt, and J. J. Villalba. 2015. Assessing the impact of supplements, food aversions, and silica on medusahead (Taeniatherum caput-medusae (L.) Nevski) use by sheep. Small Ruminant Research 124: 45-54. DOI: http://dx.doi.org/10.1016/j.smallrumres.2015.01.014
Harris, G. A. 1965. Medusahead competition. In: Proceedings of the Cheatrgrass Symposium, Vale, Oregon. Portland, OR, USA: Bureau of Land Management. p. 66-69.
Kyser, G. B., J. M. DiTomaso , K. W. Davies, J. S. Davy, B. S. Smith. 2014. Medusahead Management Guide for the Western States. University of California, Weed Research and Information Center, Davis. 68 p. Available at: wric.ucdavis.edu.
Schmelzer, L., B. Perryman, B. Bruce PAS, B. Schultz, K. McAdoo, G. McCuin, S. Swanson, J. Wilker, and K. Conley. 2014. Case study: reducing downy brome (Bromus tectorum L.) fuel loads using fall cattle grazing. The Professional Animal Scientist 30:270-278.
Young, J. A. 1992. Ecology and management of medusahead (Taeniatherum caput-medusae ssp. asperum [Simk.] Melderis). Great Basin Naturalist 52:245-252.