NATURE NOTES:
Fighting Non-Native Plants in Big Bend National Park

By Andrew Stuart

Sweeping prairies, mountain meadows, river canyons – there are places in rural West Texas that feel timeless. And indeed, such places often retain much of their primordial character. Yet no place, however remote, is untouched by the environmental changes humans have wrought in the last century and a half.

One profound change has been the spread of non-native plants – which have displaced or disrupted native plant communities, and the wildlife that relies on them.

Protected lands aren’t exempt. At Big Bend National Park, officials are charged with preserving native flora and fauna. In 2018, the park adopted a new plan for managing non-native or “exotic” plants. 

In Big Bend, exotic plants have perhaps been most pronounced along the Rio Grande. Historic photos show a broad stream, braided and meandering. Annual floods kept riverbanks open, and relatively free of vegetation.

But when the river was dammed, a century ago, annual flooding ceased. Salt cedar – an Asian plant originally introduced for erosion control – spread, and soon choked long stretches of the Rio Grande.  

In the last decade, the salt-cedar tide has turned. In the park, and elsewhere, scientists introduced one of its natural enemies – the tamarisk leaf beetle – and the insect has succeeded in fighting back the plant.

The park plan calls for continued salt-cedar vigilance. But a related plant is the “coming scourge.” 

Athel tamarisk is immense, growing 80 feet high. It’s long been planted as a shade tree. It wasn’t thought to reproduce in the wild. But in 2008, a historic flood on the Rio Grande proved otherwise.

Biologist Raymond Skiles spearheaded the non-natives plan.

“After that, it was clear there had been probably a 10-fold increase, maybe more, in the number of athel tamarisk,” Skiles said. “It’s only been in the last five years, that the park has seen we’re almost behind the curve already on those. It’s fair to say there are thousands in the river corridor.” 

Skiles said the spread of athel tamarisk seeds by another flood would mean a “wholesale shift” on the Big Bend reach of the Rio Grande. The new plan calls for aggressive action – using chainsaws to cut tamarisk, and herbicide to poison stumps.

Native to the Mediterranean region, giant river cane, or giant reed, is another exotic that’s dominated river banks. During the last decade, park staff and managers at protected lands in Mexico partnered to address giant reed. They used controlled fires to burn out thickets, and applied herbicides to kill the plants, throughout the 18-mile length of Boquillas Canyon. 

It’s made a dramatic difference, and the plan calls for expanding the efforts. The removal of giant-reed monocultures has allowed native plants to return. It’s also improved the experience for river-runners – banks that were overgrown are now accessible for camping and picnicking. Open banks give native river life – insects, mussels, fish – a better chance of survival.

“Certainly the goal is to create a habitat that does sustain the native species,” Skiles said. “It’s an incremental step, but it’s a step in the right direction.”

Giant reed and tamarisk are hard to miss – but profound threats to the park come from less noticeable plants: non-native grasses. 

Lehmann lovegrass and buffelgrass were both introduced as livestock forage. The park itself may have included lovegrass when re-seeding after highway construction. Both grasses tend to form homogenous, single-species stands. They edge out native plants, especially in the wake of wildfire.

In some parts of the park, landscapes once characterized by cacti and succulents – that diverse, if spare, tableau of desert plants – are now dominated by non-native grasses.

“In the lower desert, particularly toward the Rio Grande, there are areas where the natural environment was sparse with a lot of bare ground,” Skiles said. “Those areas are classic desert environments, and those could simply go away with the coming dominance by non-native grasses.”

It destroys habitat for desert wildlife. And it also threatens historic structures.

Exotic grasses flourish in the disturbed soils near buildings. Skiles says buffelgrass fueled the 2019 fire that destroyed the park’s historic, and beloved, Castolon Store.

There aren’t easy ways to control exotic grasses. But the plan calls for removing them near historic structures, and in specific areas, like where they threaten the endangered Chisos hedgehog cactus.

Visitors are awed by Big Bend’s wildness. Yet, ecologically, no place is an island. Safeguarding the park is complex work.

The public is invited to join Skiles Saturday morning, Dec. 7, on a field trip exploring exotic plants along the Rio Grande. Visit npsot.org/bigbend and click on “Chapter News” for details.