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Introduction

Image Details

Elkhorn Ranch (the Ranch) sits on approximately 10,000 acres in the Altar Valley of southern Arizona. The Ranch was purchased by the Miller family in 1945 as a guest ranch and cattle operation. In response to severe drought in the 1970s, the family removed cattle and focused on using the property to breed saddle horses and run a guest ranch. The ranch owners practice conservation-minded land management, and work with the US Natural Resource Conservation Service to scientifically monitor range vegetation and conduct stewardship projects. They have been engaged in a long term brush management project since 1984. 

The owners of Elkhorn Ranch and other local ranchers work collaboratively as the Altar Valley Conservation Alliance (AVCA) to care for the 600,000 plus acre watershed surrounding the Ranch. The valley is home to the Buenos Aires National Wildlife Refuge, as well as over 200,000 acres of ranch land that is part of Pima County’s conservation land system. AVCA partners work to maintain the Altar Valley as a thriving ranching community that will be sustained for future generations. 

Key Issues Addressed

Woody species encroachment is occurring in arid and semi-arid regions worldwide. In western North America, extensive replacement of grasslands by mesquite trees (Prosopis spp.) is driven by numerous interacting factors including historical overgrazing, fire suppression, and climate change climate change
Climate change includes both global warming driven by human-induced emissions of greenhouse gases and the resulting large-scale shifts in weather patterns. Though there have been previous periods of climatic change, since the mid-20th century humans have had an unprecedented impact on Earth's climate system and caused change on a global scale.

Learn more about climate change . The conversion of grasslands to shrublands can lead to decreased rangeland productivity and loss of grassland-dependent wildlife. Brush management is the practice of removing or reducing undesirable trees or shrubs, often with the goal of promoting herbaceous cover. Prior to implementing brush management, mesquite cover in the treatment area at Elkhorn Ranch was over 50% with severe gully erosion and minimal understory vegetation.

Project Goals

• Reduce woody vegetation cover to increase productivity of herbaceous species
• Slow the flow of water in gullies to minimize erosion and keep water on the landscape 

Project Highlights

Brush Has Value Too: Belts of woody vegetation left along drainages provide corridors to support wildlife movement. 

• Long-Term Treatments: Brush management treatments were implemented on 1,000 acres starting with mechanical removal of woody vegetation between 1984 and 1990. Follow-up treatments with herbicide backpack sprayers have occurred since 2002. They have used Tordon since 2002 and started using Remedy in 2004 as a follow-up treatment. Maintenance includes annual spot treatment of resprouts and seedlings using herbicide backpack sprayers.
• Beneficial Use of Brush Piles: Cleared trees were pushed into incised gullies to slow down water and help reduce erosion.
• Aerial Imagery Analysis: To assess treatment effectiveness and monitor changes in woody species cover over time, the ranch owners collaborated with AVCA and a GIS contractor to analyze aerial imagery beginning with pre-treatment conditions of 1974.
• Monitoring to Inform Management: The ranch owners have conducted annual rangeland monitoring with NRCS since 1983. Additionally, simply observing their land over time has afforded the ranch owners an intimate understanding of the landscape’s response to variable climate patterns and management practices. 

Lessons Learned

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• Though the work took place on just 10% of the Ranch, it has had a noticeable impact on rangeland condition on the remaining acreage. The increase in productivity on treated areas has allowed for greater pasture rotation flexibility, and untreated areas have seen a recovery of native grass species.
• The treatment areas are more amenable to the guest ranch operations. The reduced woody vegetation cover has made these areas more scenic, more open, and easier to traverse on horseback.
• Using prescribed fire to maintain cleared areas has proven challenging in the past due to complex planning and permitting requirements, fuel and climate conditions, fire resource availability, and liability issues. Even with these challenges, ranch managers consider prescribed fire to be a critical tool and remain committed to working through the challenges in the near future.
• The ranch owners have observed a reverse in gully erosion trends in treated and untreated areas. This is likely due to a combination of factors including increased perennial grass cover following brush removal, and the practice of pushing brush into the gullies.
• Aerial imagery analysis shows that woody vegetation cover has declined each year since treatment began. However, imagery from 2017 suggests an increase in woody cover from 1% to 5%, possibly due to growing resprouts becoming more visible, as well as an increase in pixel resolution.
• Non-native Lehmann lovegrass was part of the seed mix after the initial treatments in the 1980s. Today, Lehmann lovegrass is considered an 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 , but it was a commonly recommended species for seeding at the time. It has been effective at providing ground cover and watershed stability during and following periods of intense drought. Ranch managers have seeded with native species with varied success to establish a wider diversity of perennial grass cover. 

Next Steps

• Work with the Altar Valley Conservation Alliance partners to explore the use of prescribed fire and aerial herbicide applications
• Examine seeding strategies to increase native grass establishment

Funding Partners

• , Formerly Soil Conservation Service (1984-1990)
• (2007) 

Resources

• Robinett Rangeland Resources

Contact

• Mary and Charley Miller: mary@elkhornranch.com

Case Study Lead Author

• Ashlee Simpson, CART Graduate Research Assistant, University of Arizona

Suggested Citation

Simpson, A. C. (2018). “Over 30 Years of Brush Management on the Elkhorn Ranch.” CART. Retrieved from /project/brush-management-elkhorn-ranch.