Restoration Plan

Buffelgrass in Saguaro National Park

Visitors from around the world arrive at Saguaro National Park anticipating a breath-taking view of giant cacti and a prime example of Sonoran desert plants and animals. This splendid landscape is threatened by invasive plants, like buffelgrass (Cenchrus ciliaris). Buffelgrass, native to Africa, was brought to the U.S. for cattle forage and erosion control in the 1930s. Its rapid and aggressive growth crowds out native plants, alters wildlife habitat, and increases the risk of wildfires. Buffelgrass-fueled wildfires burn very hot, spread rapidly, and are capable of destroying cactus and wildlife alike, changing the Sonoran Desert as we know it.

Buffelgrass was first noted in the park 1989; and hand removal of this weed began in the early 1990s. Manual removal is very labor intensive, and the rapid growth and spread of buffelgrass quickly outpaced our efforts. The Park's 2004 Exotic Plant Management and Environmental Assessment Plan authorized the use of herbicides to treat invasive non-native plant species based on cost, effectiveness, and Park Service regulations. Herbicide selection is based on effectiveness versus potential impacts of the environment and non-target species. Herbicides with the active ingredient of glyphosate are very effective at killing buffelgrass, virtually non-toxic to wildlife, and do not accumulate in water or soils. However, they must by applied when plants are actively growing, which limits treatments to the monsoon season. The disadvantage of herbicides like glyphosate are that they are non-selective, and impact non-target plants.

 

The Plan to Fight Buffelgrass and Restore Native Habitat

Saguaro National Park completed a Restoration Plan and Environmental Assessment (RPEA) in 2014 that describes management actions proposed to restore native vegetation and mitigate negative impacts to park lands from damage caused by wildfire, floods,invasive species, or other large-scale changes to the environment. The RPEA, which was available for public review and comment for 30 days, included descriptions of the proposed alternatives, and identified and compared their potential environmental impacts. The preferred alternative includes all of the restoration techniques the park had been using to date, and allows for aerial (helicopter) delivery of restoration treatments to sites that are not accessible by ground crews. The National Park Service approved the RPEA with a Finding of No Significant Impact (FONSI) that took the assessment and public comments into account, and accepted the preferred alternative.

Subsequently, over 250 acres of buffelgrass infested park lands were aerially treated with herbicide between August 18-24, 2014. There was evidence of die back within a few days of treatment, and four months later it was clear that the treatment had been effective. Per the Plan, monitoring of both buffelgrass and native plants in treated areas will inform future park decisions regarding future aerial treatments. Some areas with a large seed bank will require several years of retreatment to kill new buffelgrass plants, before the native vegetation can recover.

 

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Science-based Solutions

At Saguaro National Park we are committed to evaluating the effectiveness and costs of different methods of buffelgrass control. Our research includes studies on herbicides efficacy and toxicity on both buffelgrass and non-target native vegetation and wildlife, such as desert tortoise. The Park has also funded studies on the use of remote sensing techniques, such as satellite imagery, to identify and monitor buffelgrass and its fuel loads, and we are also developing computer models to predict buffelgrass spread and buffelgrass-fueled fire behavior.

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Series of "drift cards" set out to record herbicide drift. They are 4 x 6 inch water sensitive cards that show each drop that hit them. We put them out around sprayed areas to ensure that the buffelgrass patches are hit and drift off site is minimized.

Left image
This drift card was placed in the center of the intended dropzone.  Notice the big, rain sized droplets.  The weight of the drops is enough to fall straight down onto the intended area.

Right image
This drift card was placed 15 feet away from the intended drop zone.  Notice how little herbicide drifted 15 feet.

 

Success - at a Small Scale

Our ground-based control efforts include manual pulling of plants, and spraying herbicides with backpack in areas accessed on foot. Through a process called adaptive management (assessing the results of our actions to ensure that our goals are met without unacceptable side effects, and adjusting our strategies accordingly), we've learned that to successfully control buffelgrass, treatments must occur several times a year for up to five years.

Constrained by factors such as inaccessibility, a limited treatment window, and the need for repeated treatments, there was little hope of controlling the estimated 2,000 acres of buffelgrass growing in 2014 throughout the park by ground-based efforts alone. At a predicted spread rate of 10% - 35% annually, we simply cannot keep up with the growth of buffelgrass.

 

Helicopter with a boom sprayer applies herbicide over buffelgrass.  The rain drop sized droplets are heavy enough to fall directly to the ground.  Application is suspended if winds exceed 10 mph to prevent herbicide drift from the target area.

Next Step

In 2010, we partnered with other local, state, and federal agencies to evaluate the use of helicopters to deliver herbicides for buffelgrass control. Both a boom mounted to the underside of a helicopter, and a "spray ball" tethered from a helicopter, proved to be effective delivery mechanisms for the herbicide. The boom application is appropriate for treating large infestations that no longer support native plant communities; and because of its precision, the spray ball is ideal for treating small infestations. Follow-up studies of this treatment found that many native species, particularly cacti and trees, were largely unaffected by glyphosate (see links below).

Per the 2014 RPEA aerial herbicide treatments proposed only for remote and difficult to access sites that are dominated by (>50% cover). Aerial spraying of herbicides will not occur within a quarter-mile of occupied private property, one hundred and sixty-five feet of a spring or other water source, or in areas above six thousand feet elevation.

We will continue to monitor treated areas to evaluate the effectiveness of aerial spraying, and to identify and mitigate negative impacts.