Thursday, Feb. 23, 2006 | 7:11 a.m.
Nevada is under siege. And we welcomed the attack.
While little-noticed by the urban denizens of Southern Nevada, an assortment of plants and animals is destroying elements of the desert ecosystem.
Many of those invaders are hitchhiking rides from people who are out to enjoy the desert, but could end up destroying what they have come to see. Other species, especially animals, have been deliberately introduced as game or even as bait.
Either way, the invaders are wiping out native species and costing taxpayers millions. The plants make conditions ripe for devastating wildfires, while the aquatic invaders are rapidly replacing species that made Nevada's streams and lakes their homes for eons.
The "Who's Who" includes red brome and cheat grass, related species that fuel wildfires in areas that once resisted such fires; Sahara mustard, growing fat on the sides of roads; crayfish in clawholds throughout Southern Nevada; bullfrogs in the region's warm springs; tilapia in Lake Mead and its tributaries; and salt cedar sucking up huge amounts of water as it takes over stream banks.
The victims of the invading species are native fish, plants and animals.
Also feeling the burn from these invaders, most of them from Europe and Asia, are taxpayers, mostly because the plant invaders have turned Southern Nevada into a tinderbox.
Pete Anderson, state forester for the Nevada Forestry Division, said invasive grasses helped fuel fires that swept through 1.1 million acres in the state and 750,000 acres in the southern half last year.
In an average season, less than a third of that would burn, he said.
As the amount of blackened acreage goes up, so do the costs. The division doesn't have an estimate yet of the cost for last year's firefights, but Anderson said he would expect it to be considerably higher than the average cost of $50 million.
"I don't think we've ever had fire of the magnitude we had in the Mojave last year," Anderson said. "The forecast for this season is not a lot better."
Anderson agrees with scientists who have concluded that invading grasses - which provide little forage for wild horses, wildlife or cattle - are responsible for the worsening wildfire situation.
John Hiatt, chairman of the Red Rock Audubon Society's conservation committee and a well-known Las Vegas conservationist, said he has seen great change in the desert over the last decade.
"Fire was virtually unheard of in the Mojave ecosystem until you got some of this non-native vegetation," he said. "The worst fire year in Mojave history was 2005.
"These non-native plants are very well fire-adapted. The native vegetation is not resistant to fire. When it's burned, it's gone."
Among the species threatened by invading grasses and mustards is the Joshua tree, the distinctively gnarled and twisted resident of much of the region.
"Joshua trees, those are wonderful, supporting a lot of biological diversity, a lot of mammals, a lot of birds, and they're aesthetically pleasing," said Stan Smith, a UNLV biology professor. "We are looking at losing that and having it replaced with exotic grasslands.''
The newcomer animals are an odd and diverse lot. "Crayfish, aquarium fish in general, bullfrogs and tilapia - those are the top ones," said Jon Sjoberg, a Nevada Wildlife Department biologist.
Crayfish, the same species that one will find in a Louisiana gumbo, are making themselves at home throughout Nevada and the Great Basin - and wiping out their native competitors.
"There are no crayfish native to Nevada or the Great Basin," he said. "They've now started showing up all over the place. They just hammer everything. They're just really, really difficult to get rid of."
Sjoberg said that among the animals getting hit hard are the Moapa dace, a 3-inch, federally protected and endangered fish that lives in Clark County's Muddy River.
Another rare animal, for which conservationists are seeking federal protection, is the native relict leopard frog, which is estimated to have a population of about 1,000 left in the wild. Scientists believe the species is on the edge of extinction.
Sjoberg said that while scientists and conservationists are most concerned about rare and threatened native species, virtually any fish or amphibian that lives in Southern Nevada's springs and wetlands can fall prey to the onslaught of invaders.
Like other invading plants and animals, crayfish are getting help from people to take over new habitats.
"They have a limited ability to move over land in wet weather, but the ability of red swamp crayfish to get from Lake Mead to Beatty is probably pretty limited," Sjoberg said. "We assume people are moving them."
Tilapia, once native to Eurasia, are potentially beneficial sources of fish protein, but they are menaces to local fish and aquatic plants. Sjoberg said tilapia, which were deliberately introduced into the lower Colorado River, have adapted well to Lake Mead and moved into the Muddy and Virgin river tributaries. Along the way, they are threatening the already precarious existence of small native fishes.
"They're a good fish for aquaculture, and that's how I like them, in frozen fillets," Sjoberg said.
"They're a very bad thing in the wrong place, and the lower Colorado River is the wrong place," he said. "They're extremely aggressive. They dominate these habitats. They'll strip out vegetation and cover. And they're not just herbivores."
People are also responsible for introducing what might be the most bizarre new inhabitants of Nevada's lakes and rivers - common aquarium fish. Many springs throughout Nevada are heated by geothermal processes, essentially creating warm-water oases for mollies, convict cichlids, tetras, suckermouth catfish and other common aquarium fish.
"People think they're doing their fish a favor by releasing it into the wild and not flushing it down the drain," Sjoberg said. "But these are very aggressive. Not only are they predators, they're competitors as well.
"All kinds of weird stuff is showing up out there."
Sjoberg said 18-inch suckermouth catfish have turned up in Las Vegas Wash.
"They're potentially reproducing," he said.
People who don't spend a lot of time outdoors may not have seen the changes to the environment, but they are happening, Sjoberg said. Mule deer, for example, are finding it tough to survive in the new ecological regime.
"In the past 20 to 30 years, we have seen almost an entire ecological shift," he said. "People ask, 'Where are all the deer?' We say, 'What happened to the habitat?' "
Scientists and state and federal officials are generally pessimistic about getting rid of the invading species that are already here.
"Once it's there, it's extremely difficult to get rid of," Brett Riddle, a UNLV biologist, said about invading plants. "We need to be extremely proactive about preventing the possible spread beyond where it is right now."
One way to do that is to keep off-road vehicles out of designated areas of critical environmental concern, Riddle said. The scientist said he's not opposed to all off-road activities, but is concerned that the vehicles can introduce seeds into areas that have so far been spared the invasions.
Matt Brooks, a research botanist with the U.S. Geological Survey's Henderson laboratory, said the response to the invasion of plant species is, at this point, to curtail the damage.
Weed-control efforts can help but can't eliminate the problem species, he said. Nevada residents, including professional horticulturists, need to prevent new invasions by making sure that non-native species don't leave back yard gardens.
"The most effective strategy is to deal with the problem before it becomes a problem," Brooks said.
Riddle said people have a way of changing the environment.
"They do it without thinking," he said. "There's so much we do out there without thinking, it's unreal. We really need a crash course - particularly in this city where everybody is from somewhere else - in the sensitivity of arid lands."
Launce Rake can be reached at 259-4127 or at [email protected].
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