Tumbleweeds are a familiar sight in arid and semi-arid regions, often seen rolling across open landscapes. These are not a specific plant species, but a growth habit adopted by various plants, such as Russian thistle (Salsola tragus), once they reach maturity and detach from their roots. This detachment allows the dead plant material to be propelled by wind, effectively dispersing its seeds across wide areas. Their presence raises questions about what consumes them.
Animals That Consume Tumbleweeds
Livestock, including cattle, sheep, and goats, sometimes consume tumbleweeds, especially when other forage is scarce, such as during droughts. Young, green tumbleweed plants are more palatable and less fibrous than mature ones and contain some nutritional value. They can provide protein, vitamin A, and phosphorus, with some reports indicating that the protein content can even increase in their dry, winter state for goats.
Despite some nutritional content, mature tumbleweeds are generally not a preferred food source for livestock. These plants develop sharp spines as they mature, which can cause physical irritation to an animal’s mouth and digestive tract. Additionally, certain tumbleweed species, like Russian thistle, can accumulate high levels of nitrates and oxalates, particularly when stressed by drought or other environmental factors. Ingesting too much of these compounds can lead to nitrate poisoning in ruminants like cattle and sheep, a serious condition that prevents red blood cells from carrying oxygen.
While livestock may consume tumbleweeds under specific conditions, wild animal consumption of the mature, dry form is less common. Some wildlife, such as mule deer, pronghorn, and prairie dogs, may eat the tender, young shoots of tumbleweeds. However, once the plant dries, its palatability and nutritional appeal diminish significantly for most wild herbivores. The tough, spiky texture and potential for toxicity further deter consistent consumption by most species.
Insects, Microbes, and Other Factors
Insects and microbes also play a role in the breakdown and consumption of tumbleweeds. Certain insect species are specifically studied for their potential in biological control efforts against invasive tumbleweed species. For example, the eriophyid mite, Aceria salsolae, is a biological control agent that attacks Russian thistle, stunting its growth and damaging its tissues. Their activity damages the plant, making it less viable and more susceptible to decomposition.
Microorganisms, including fungi and bacteria, are primary decomposers of dead plant material, and tumbleweeds are no exception. Once a tumbleweed comes to rest, these microbes colonize the plant material. They produce enzymes that break down complex organic substances like cellulose and lignin. This microbial activity is essential for recycling nutrients back into the soil, completing the natural decomposition cycle.
Tumbleweeds are not a preferred food source for many organisms. Their high fiber content makes them difficult to digest, and the sharp, spiny structure of mature plants deters grazing. Furthermore, some species or stages of tumbleweeds can contain compounds that are unpalatable or potentially toxic. As dead plants, they lack the moisture and fresh nutrients that most herbivores seek.