Invasive Cheatgrass (Bromus tectorum)



Since Bromus tectorum has invaded in several parts of the world there are several other organism and species that it encounters or has an effect on. Again, there are so many that I couldn’t possible catch them all, but we will look at many interactions that go on in this invasive species life. 

Let’s start with something smaller. Cheatgrass is known to host over one hundred units of endophytic fungi; the grass acts as a host for the fungi. A fungivorous nematode, Paraphelenchus acntioides, and an endophyte, Fusarium cf. toulosum, are two other microscopic species that are associated with B. tectorum. It is proposed that the fungivourous P. acontioides uses living plants, like that of Cheatgrass, to increase the amount of the desired fungus on the plant (Baynes et al. 2012). Cheatgrass plants might also be inhabited by vesicular-arbuscular mycorrhizal fungi. It is also commonly known to be infested with a head smut fungus, Ustilago brominvora. This fungus can temporarily reduce the amount of Cheatgrass on some sites; it does this by colonizing the seeds and roots and then produces a toxin that apparently puts cell growth to a halt in new growing plants (Zouhar 2003). For more information on the fungal interactions, take a look at the Prevention Page.

Some other interactions that B. tectorum goes through is the grazing by cattle, horses, and sheep (Forest and Range 2006). Cheatgrass can tolerate repeated grazing, but it becomes an issue when it turns to heavy grazing because it destroys its ability to invade as efficiently via seed production. After about 8 weeks in the digestive tract of cattle the Cheatgrass seeds can no longer reproduce or grow (Zouhar 2003). However, there are times where excessive grazing can help B. tectorum expand because the cattle, or whatever else is eating it, are also eating the perennial plants. When this happens it allows the Cheatgrass seeds to dominate the land during its next growing season (Zouhar 2003).

Uses for other Species
Cheatgrass is not always a bad thing. It is a food source and home for many animals. In the winter, fields of B.tectorum turn to a bed and some “hay” for several cattle and horses. These animals would prefer to have something else, due to the grass being an inadequate source of protein, but they would eat that over starving (Zouhar 2003). Cheatgrass is also a viable food source for lamb ranges (Zouhar 2003). When dry Cheatgrass is being eaten by livestock the animals need to be watched more closely. As the grass matures it dries out and the seeds become sharp; this can be a hazard to animals because it increases the occurrence of mouth infections and eye injuries (Zouhar 2003). Several other animals use Cheatgrass as a source of food. Some examples include: ground squirrels, pronghorn, mule deer, bighorn sheep, montane meadow mice, several birds, other small mammals, and insects. They all use the invasive grass as a way to live and in the mean time they are shaping the land of where the grass intends to grow (Zouhar 2003).

Usually with some positive news come some bad new too. So let’s see how B. tectorum is also a harmful species in other ways than just its invasiveness. Some native plant and animal species that live among Cheatgrass are at risk of going extinct (Zouhar 2003). The amount of fires that happen due to this invasive species is eliminating important food sources for many of the deer and elk. With only having Cheatgrass as the main source of vegetation, the biodiversity of all herbivores and carnivores is being reduced due to lack of resources (Zouhar 2003). Cheatgrass is also associated with the decline of many small mammal populations, and there are two factors that limit this. The first is increased predation due to loss of shrub coverage and the second is the thickness of the fields might be blocking and trapping young mammals, leaving them for death. Loss of smaller mammals can just have a domino effect on the food chain because the species that were feeding on them are now losing their food source. Unless they adapt or find another food source, larger species will start to be effected too (Forest and Range 2006).
            Cheatgrass has even become a problem in alfalfa and wheat fields in the winter. Since it can survive and reproduce in colder temperatures they invade the farm lands while the crops are lying dormant (Forest and Range 2006). The biomass of these crops can be significantly lowered. To fix this, it has been suggested that certain perennial grasses, like bluebunch wheatgrass, bottlebrush squirreltail, Elymus elymoides, and a few others can be introduced to a field of B. tectorum and they have a chance of being a source in an ecological restoration process (Zouhar 2003). These grasses have a competitive impact on Cheatgrass and slow down its growth and reproduction.


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