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Study: Invasive Plants Threaten to Push Animals Out, Wildfires Into Southwestern United States

82 percent of America’s three largest national parks are infested with at least one type of foreign foliage that’s ripe for becoming brushfire kindling.

Research  |  Jul 10, 2015  |  By Keyonna Summers
dry grass at red rock canyon

Dead stalks of the non-native grass red brome (Bromus rubens) provide dry tinder for fueling wildfires across southern Nevada landscapes like here at Red Rock Canyon.  Red brome is an annual plant, meaning it germinates, grows, and dies all in the same year.  It produces more abundant fuel that lasts longer than native annual wildflowers and grasses.  As a result, fuel conditions and wildfires have become more severe in recent decades in the Las Vegas area desert. (Aaron Mayes/UNLV Photo Services)

Welcome to summer in the desert southwest! Is it hot enough for you out there? Well, brace yourselves because new data released by UNLV scientists shows that uncontrolled growth of invasive plants in Southern Nevada, California and Arizona is threatening to turn up the heat on wildfires.

Researchers studied Mojave National Park, Death Valley National Park and Lake Mead National Recreational Area and found that foreign plants and grasses are disrupting the parks' ecosystems. The invasive plants are crowding out and killing off native vegetation and harming the animals that eat them, before dying and becoming fuel for wildfires.

The potential for disaster is apparent, scientists say, considering the research area spans nearly 6 million acres (or 23 percent of national park land in the contiguous United States) and a whopping 82 percent of plots were found to harbor at least one invasive species.

Red brome -- a type of grass known for altering fire patterns by increasing flames' spread and intensity -- was the biggest culprit, infesting 60 percent of plots and leaving dead stalks standing upright for as long as two years. Other plant invaders included redstem filaree, Mediterranean grass, prickly Russian thistle, Sahara mustard and saltcedar. Researchers found that 30 percent of plots contained two types of foreign plants, 17 percent contained three and 4 percent contained four to 10.

And it's not just a problem for forest rangers far removed from the bright city lights. Researchers say invasive desert flora played a role in blazes right here in the Las Vegas Valley, where landscape changes exacted more than a decade ago at the famed Red Rock hiking, bicycling and picnic area on the western outskirts of town are still visible.

The UNLV paper, recently published in the peer-reviewed journal "Nature Conservation," offers tips to start phasing out non-natives:

  • Enhance visitor education, and introduce ways for park visitors and staff to report infestations
  • Save money and time by addressing invasive infestations at the same time as other park problems, such as air pollution
  • Dedicate more resources to fighting non-native plants

But what if that doesn't happen? We spoke with UNLV ecologist and study lead author Scott Abella about the possible impact on both locals and tourists:

1. How did red brome and other non-natives mentioned in the study end up in these parks?

Many non-native plants were introduced to the United States over 100 years ago. Some plants were intentionally introduced for purposes such as to feed livestock. Other plants were inadvertently introduced, like "stowaways" in seeds of agricultural crops. Some of the non-native plants in the national parks we studied may have even been introduced by Spanish missionaries in the 1500s.

2. Why should we as residents, tourists or nature lovers care about these non-native plants?

When many non-native desert plants die, they produce an unnatural amount of dried out material and pose a severe risk of fire. Several of the wildfires in the past 10 years around Las Vegas, including in Red Rock Canyon National Conservation Area, were partly fueled by dead non-native plants. Scenery at Red Rock remains altered by fires that occurred over 10 years ago. These non-native plants also have other ecological impacts. One example is that an iconic species of the Mojave Desert around Las Vegas -- the desert tortoise -- avoids eating non-native grasses whenever possible. Instead, tortoises prefer foraging on native plants, which are being impacted by crowding out by the non-natives.

3. Why should national park managers care?

National parks occupy only 1.3 percent of the lower 48 states. In this small fraction of the United States, nature is supposed to be authentic - where natural processes and native species predominate. Invasion by non-native species threatens the very ideal of national parks. As a result, trying to reduce non-native plants is one of the main conservation strategies being undertaken in national parks.