Cheatgrass is an ecosystem transformer.
Photo credit: Becky Kerns
Reintroducing fire is considered critical for the restoration of many fire-dependent forest ecosystems. But, although it can bring many benefits, fire is a disturbance that can also create undesired consequences such as the invasion of noxious weeds.
Noxious weeds, also known as invasive exotic plants, are nonnative species that often outcompete native plants for water, nutrients, and space. Left unchecked, invasive weeds can significantly impact the well-being of an entire ecosystem.
Ecologist Becky Kerns studies how disturbances shape the composition and function of forest and rangeland plants. She led a study with colleague Michelle Day on cheatgrass and how it responds to the frequency and season of prescribed burning in ponderosa pine forests. Cheatgrass is an invasive annual grass that is known as an ecosystem “transformer” because of its potential to drastically disrupt ecosystems.
Kerns and Day found that after 10 years, cheatgrass cover increased with fall burning regardless of burn frequency. The existence of native perennial grass cover constrained the extent and impact of cheatgrass invasion, but only when initial cheatgrass abundance was low. Their work suggests that perennial grasses may be important for limiting invasion extent and impact, but native annual forbs may be important for limiting initial spread at fine scales in repeatedly disturbed environments. However, they caution that the successful establishment of native annuals is often limited to specific annual precipitation conditions, which might limit their ability to repel invasions.