Impacts of invasive plant removal treatments on bird and butterfly communities in a desert riparian floodplain ecosystem

PARTNERS: National Park Service (NPS); Wood Lab of Avian Ecology and Conservation at Cal State University, Los Angeles

SUMMARY: Eastern Threat Center ecologist Lars Pomara is working with partners to understand how bird and butterfly communities respond to ongoing ecological restoration efforts in riparian habitats in the floodplain of the Rio Grande, in Big Bend National Park, on the Texas/Mexico border. This work has been supported by grants from the National Park Service’s Southwest Border Resource Protection Program.

The Rio Grande riparian system is one of the most significant of its kind in the U.S. Southwest and northern Mexico, providing habitat for a wide array of plant, fish, and wildlife species. The river and its floodplain have changed dramatically over the past century due to water diversion for agricultural irrigation, damming, urban expansion, floodplain agriculture, and other impacts.

Pictured: Riparian floodplain vegetation along the Rio Grande/Bravo in Mexico and Texas. Photo by Lars Pomara, U.S. Forest Service.

These changes have facilitated the spread of invasive plant species, which further alter river hydrology and cause important changes in floodplain vegetation and habitat conditions for wildlife. Over the past several decades large stands of giant cane (Arundo donax) have come to dominate significant portions of the riverbank in both the United States and Mexico, exacerbating stream channelization through bank armoring, and displacing more diverse native vegetation. Big Bend National Park in west Texas and adjacent protected areas in northern Mexico have undertaken a major restoration initiative, using prescribed fire and manual treatments to remove giant cane stands along 118 miles of shared river floodplain. A recent New York Times story highlighted this difficult work in a visually stunning way.

Pictured: Giant cane invades the banks of the Rio Grande/Bravo in Big Bend National Park, Texas. Photo by Heather Mackey.

With support from the National Park Service, Pomara and collaborators at Cal State L.A. are assessing the impacts of the restoration efforts on floodplain wildlife by monitoring the status of the bird and butterfly communities in relation to vegetation treatments. During 2016 and 2017, researchers began establishing a baseline understanding of how bird and butterfly species composition and diversity vary across the landscape with variations in habitat, and are now examining how these community characteristics change when the treatments alter the vegetation. A species of particular concern is the Yellow-billed Cuckoo (Coccyzus americanus), whose western population was recently listed as threatened under the U.S. Endangered Species Act. In addition to community-level monitoring, researchers are examining habitat relationships across the landscape and over time for this species and other select riparian-associated species. NPS partners hope to use resulting information about the distribution of high-quality floodplain habitat to inform Yellow-billed Cuckoo management, and other regional state and private conservation partners should also benefit from these findings. Throughout the Chihuahuan desert region in the United States and Mexico, river floodplain vegetation is one of the highest-priority wildlife habitats in terms of its high biological diversity as well as the variety of threats that are posed to its conservation. Monitoring the status of its wildlife to inform management decisions therefore also remains a priority.

Pictured: Reakirt’s Blue butterfly nectaring on Tamarisk (salt cedar), a non-native invasive woody shrub/tree in North American desert riparian systems. Photo by Eric Wood.

EFETAC'S ROLE: This project is supported by Eastern Threat Center research.

STATUS: Initiated 2016; Ongoing.

PROGRESS: Project annual reports have been submitted to the National Park Service in spring of 2017 and 2018. In spring/summer 2018, Heather Mackie and Julie Coffey each completed their Master’s Thesis on this project, in Eric Wood’s lab at Cal State L.A. Peer-reviewed publications are underway.

Pictured: Mackie and Coffey survey birds in a recently burned Giant Cane stand. Eradication typically requires repeat burns (Big Bend National Park, Texas). Photo by Eric Wood.

Project annual reports to the NPS:

Mackie, H., J. Coffey, E.M. Wood, and L.Y. Pomara. 2017. Bird and butterfly community response to large-scale invasive plant removal and native plant restoration in desert riparian habitat along the Rio Grande/Bravo, Big Bend National Park, Texas. 2016 annual report to the National Park Service.

Coffey, J., H. Mackie, L.Y. Pomara, and E.M. Wood. 2018. Bird and butterfly community response to large-scale invasive plant removal and native plant restoration in desert riparian habitat along the Rio Grande/Bravo, Big Bend National Park, Texas. 2017 annual report to the National Park Service.

Project publication

Removing invasive giant reed reshapes desert riparian butterfly and bird communities

CONTACT:

Lars Pomara, Eastern Threat Center Ecologist, lazarus.y.pomara@usda.gov or (828) 257-4357

Updated June 2018