Lehmann lovegrass (Eragrostis lehmanniana) is a non-native grass introduced into Arizona in the early 1900s to control erosion and provide forage for cattle. It covers of thousands of acres in southeastern Arizona. It creates fuel loads several times heavier than what the native grassland and savannah in this area contained, and generates abnormally intense fires. In addition to increased threat to homes and property in the wildland-urban interface, usually fire-tolerant plant species can be adversely impacted, especially agave. Parry's agave and Palmer's agave are major nectar sources for the endangered lesser long-nosed bat.
Approximately 15% of Coronado National Memorial is heavily infested with Lehmann lovegrass. Not only is the lovegrass negatively impacting native plant and animal communities, it is a threat to adjacent private homes, the Memorial's headquarters and visitor center, and the park's main evacuation route. An experiment was devised in an attempt to deal with this hazard. Recent research has indicated that fire and herbicide used in combination might be an effective management tool for Lehmann lovegrass. Native grasses and agave have been shown to respond most favorably to fire during the natural fire season, just prior to monsoon rains.
In June 2009, fire managers conducted a prescribed burn of about 35 acres in the Memorial. This was the most heavily-infested part of the Memorial, and directly adjacent to two private residences. In July and October, following monsoon rains, the post-emergent herbicide glyphosate was applied to 15 acres using backpack sprayers. On 5 acres, the pre-emergent herbicide imazapic applied to kill germinating lovegrass seedlings.
Left: Firefighter igniting a flanking fire in heavy Lehmann lovegrass near velvet mesquite trees. NPS photo by Perry Grissiom, June 2009.
Middle: A Palmer's agave, immediately after the prescribed fire.NPS photo by James Leckie, June 2009.
Right: Same agave, one year post-burn. NPS photo by James Leckie, July 2010.
Pie charts showing plant community change one year after burning and herbicide application. The target (non-native Lehmann lovegrass, in red) decreased from 67% cover to 22% cover. Native plants increased from 13% to 55% cover.
Monitoring in 2010 showed that Lehmann lovegrass was greatly reduced and that native plant cover greatly increased. Most of that increase was among native annual forbs. Use of the pre-emergent appeared to have little or no impact. Monitoring will continue to determine if native perennial plants, especially grasses, recover, and Lehmann lovegrass is held down. Additional herbicide application is being considered for summer 2011 to help recovery.
Only 29 agave were found in the burn unit, and they suffered 28% mortality. Most mortality was of small agave located in heavy Lehmann lovegrass fuels.
Contact: Perry Grissom, Fire Ecologist
Phone: (520) 733-5134
*This story supports the National Fire Plan
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