Novel Approaches to Fuel Breaks & Invasive Species Management

Introduction

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The Sonoran Desert spans across the southwestern United States and northern Mexico and is the most biodiverse desert in the world, known for its iconic saguaro cacti (Carnegiea gigantea). The Sonoran Desert is a semi-arid desert, with bimodal precipitation patterns that include summer monsoon rains and temperate winter storms. The vegetation structure structure
Something temporarily or permanently constructed, built, or placed; and constructed of natural or manufactured parts including, but not limited to, a building, shed, cabin, porch, bridge, walkway, stair steps, sign, landing, platform, dock, rack, fence, telecommunication device, antennae, fish cleaning table, satellite dish/mount, or well head.

Learn more about structure in the Sonoran Desert is naturally sparse and open, with large gaps between established perennial plants. 

Invasive perennial grasses that were introduced to the Sonoran Desert for erosion mitigation now threaten to alter the fire regimes of the landscape and convert the desert into a grassland ecosystem. Buffelgrass (Cenchrus ciliaris) is a warm-season, non-native perennial grass that originates from regions of Africa, Asia, and the Middle East. The lesser-studied stinknet (Oncosiphon pilulifer) is a non-native forb from southern Africa. Both plants threaten the natural Sonoran Desert ecosystem by outcompeting native plants for space, soil nutrients, and water resources, and by creating new, more frequent fire regimes that native plants are not adapted to. 

Fire regimes in the Sonoran Desert are not well-studied, leading to disagreement about the historic frequency, size, and severity of fire. Fire regimes are thought to be between 250 and 1000 years, depending on the distribution of native vegetation in an area of interest. However, it is agreed that the Sonoran Desert is not adapted to fire at its current frequency. 

Siphon Draw Environmental Services (SDES) started various projects around the city of Apache Junction, Arizona in 2021, to study the effects of invasive species invasive species
An invasive species is any plant or animal that has spread or been introduced into a new area where they are, or could, cause harm to the environment, economy, or human, animal, or plant health. Their unwelcome presence can destroy ecosystems and cost millions of dollars.

Learn more about invasive species within the Sonoran Desert and find novel solutions to developing fuel breaks by managing invasive species in response to the “grassification” of the Sonoran Desert. These projects include ecosystem restoration, mitigating invasive grasses and forbs by placing wood chips on the landscape, torching plants, and removing vegetation by hand.

Key Issues Addressed

Hotter, drier climate patterns have heightened the risk of ignition in the Sonoran Desert: summer monsoons have brought less water and winter months are becoming warmer, leading to longer fire seasons. Since native vegetation in the Sonoran Desert did not evolve adaptations to fire, it often dies when ignition occurs. The ecosystem is not adapted to withstand fire, especially at its current heightened severity, more frequent interval, and increased size.

The Sonoran Desert is a fuel-limited landscape, meaning that it naturally has the right weather conditions for fire to be present in the ecosystem, but fire cannot be spread very far due to the sparse distribution of fuels. Non-native perennial grasses and forbs disrupt the natural distribution of fuels by creating fuel continuity across natural desert fuel breaks, allowing fire to quickly spread across the landscape. However, invasive species in the Sonoran Desert are so abundant that it is now impossible to completely eradicate them from the ecosystem. It may be more realistic and cost-effective for land managers to focus on invasive species management solutions in heavily invaded areas rather than striving for complete eradication.

Project Goals

• Develop fuel breaks that cause minimal impact on the native ecosystem and establish fire resilience if a fire is ignited.
• Explore methods of invasive species management that emphasize creating minimal soil disturbances, restoring and maintaining the natural vegetation distribution of the Sonoran Desert, and do not rely on using herbicides for cases where herbicide use is not appropriate.

Project Highlights

• Establishing Fuel Breaks for Fire Resistance: The Lost Dutchman Fuel Break Project established new fuel breaks on Bureau of Land Management ground to mitigate the spread of fire if an ignition were to occur. Chainsaws and pruning hand tools were used by SDES project staff to remove abundant vegetation from the fuel break while leaving a majority of native vegetation intact. Most vegetation removal was done 15 feet from the property fence line, with less vegetation removed 15 to 150 feet from the property fence line.
• Mulching to Stop New Plant Establishment: Wood chips were thickly layered across plots to stop new growth of stinknet. Wood chips can burn when a fire is started; however, the fire burns at a lower severity than a grass fire. By using wood chips, the naturally sparse distribution of fuels can be maintained and new growth of invasive grasses and forbs is inhibited. Using wood chips can also reduce the amount of “green waste” produced during the creation and maintenance of fuel breaks that needs to be taken off-site or burned.
• Torching to Disrupt Horizontal Fuel Continuity: SDES project staff used portable propane tanks to torch fine fuels after removing heavy woody material and invasive grasses with large biomass such as buffelgrass and fountain grass. Removing fine fuels with torches in fuel breaks helps slow the spread of future fires by creating a mosaic of burned and unburned vegetation that disrupts the continuity of continuous fine fuels leaving the natural structure of native desert plants intact.

Lessons Learned

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Grassification Threat: The increased fire risk in the Sonoran Desert is not because of excessive fire-suppression, but rather because of the increase in non-native, fire-adapted grasses and forbs.

When deciding what vegetation to remove in fuel breaks, SDES considers plant relationships between trees and understory vegetation. After the Lost Dutchman project in 2021, SDES learned that aggressively removing vegetation via cutting and limbing can enhance the growth of invasive species. SDES now seeks to only remove enough vegetation to restore the historical distribution of vegetation on the landscape, before the presence of invasive species. Because there are few studies from the Sonoran Desert about creating fuel breaks, it was difficult to identify which plants should be prioritized for removal. SDES decided to leave standing dead ironwood trees in place to provide habitat for native animal species, such as lizards and cavity-nesting birds. 

When thinning and removing dead wood from established plants in fuel breaks, ensuring that all burning happens on disturbed soil can help reduce the risk of non-native species encroaching in new areas. However, pile burning can have adverse impacts on air quality due to smoke production from the fire. Turning removed wood biomass into wood chips to use on the landscape can reduce environmental impacts, including soil disturbances and air quality effects. However, if wood chips are layered too thin, new plants can grow despite limited sunlight for the seedling. 

Staff at SDES have learned that frequent communication across agencies and jurisdictional boundaries is important to establish collaborative approaches for invasive species management. Regular communication about invasive species assists land managers in understanding how the Sonoran Desert is changing and actions that can be taken to create and manage fuel breaks. Without communication and collaboration between landowners, unmanaged landadjacent to treated land will still be susceptible to high-severity, ecosystem-damaging fire and cause fire risk across property boundaries. Additionally, communication with a wide range of partners can provide land managers with alternative ideas and approaches to managing invasive species. 

Through the various projects that SDES has implemented, they have learned that fuel breaks need to be maintained regularly once developed, to retain their efficacy for firefighters using them to control fires. Without routine maintenance, non-native species can re-establish and spread, rendering the fuel break ineffective. To create fuel breaks in the Sonoran Desert, SDES currently recommends first removing large fallen and dead vegetation from the fuel break during fall or winter months. Then, starting the following spring, burning twice a year to clear out fine fuels and invasive species from the fuel break. Routine maintenance and monitoring of the site will ensure that the fuel break is still effective for firefighter use.

Next Steps

• Work with graduate students to study the long-term effects of various techniques to create and maintain fuel breaks including herbicide usage, experimental mulching, and propane torching treatments on invasive species growth. Research goals are focused on finding effective alternative solutions to managing invasive species with minimal impact on the Sonoran Desert ecosystem.
• Investigate whether burning with propane torches can sterilize seeds of stinknet and other invasive plants.
• Explore employment opportunities for unsheltered populations: This would include payment to harvest wild medicinal plants and prune vegetation.
• Continue to study current fire regimes and develop an understanding of what beneficial fire looks like in the Sonoran Desert: Studying fire behavior in the desert will allow the development of tailored fire prescriptions to begin easing the Sonoran Desert into an ecosystem that is more fire-tolerant and causes minimal impact to the native ecosystem.
• Monitor the effectiveness of new projects and incorporate lessons learned into adaptive management strategies.

Funding Partners

• Siphon Draw Environmental Services
• Arizona Department of Forestry and Fire Management Healthy Forest Initiative
• City of Apache Junction

Resources

• Zouhar et al. (2023). “Fire Regimes of Sonoran Desert Scrub Communities” Fire Effects Information System [Online].
• Wilder et al. (2021). “Grassification and Fast-Evolving Fire Connectivity and Risk in the Sonoran Desert, United States” Frontiers in Ecology and Evolution. Vol. 9
• Tucson Audobon Stinknet Information Webpage
• Arizona-Sonora Desert Museum Buffelgrass Information Webpage
• Lost Dutchman Fuel Break Report
• Enhancing the Natural Patchiness of the Sonoran Desert as a Fire / Fuel Break Option Summary Report
• Southwest Fire Science Consortium Sonoran Desert Grassification Webinar
• Southwest Fire Science Consortium: Sonoran Fuel Breaks Storymap

Contacts

Alan Sinclair, Siphon Draw Environmental Services: siphondrawenvironmental@gmail.com

CART Lead Author

Alexandra Gerber, CART Student Author, University of Arizona

Suggested Citation

Gerber, A., L., Sinclair, A. (2024). “Novel Approaches to Fire Breaks and Invasive Species Management in the Sonoran Desert.” CART. Retrieved from https://www.fws.gov/project/novel-approaches-fuel-breaks-invasive-species-management.