Under the direction of Morgan Treadwell, Ph.D., associate professor and AgriLife Extension range specialist, San Angelo, graduate student Deann Burson is working to shed light on how range management practices, such as prescribed fire and herbicide application, affect the concentrations of secondary metabolites in woody species including mesquite, redberry juniper, lotebush and algerita.
“Secondary compounds are not directly related to the plant’s overall growth and development but can have important benefits like protecting the plant from being grazed or browsed by herbivores,” Burson explained. “They can also attract pollinators and help the plant recover from injury.”
Burson, who is pursuing a Ph.D., said concentrations of these secondary metabolites, such as alkaloids, terpenes and phenolic compounds, affect plant palatability among livestock.
Currently, she is focused on mesquite—a highly competitive species that, without management, can quickly establish a monoculture across grazing lands.
Burson recently presented initial findings on secondary metabolites found in mesquite sprouts following a prescribed burn during a Three-Minute Thesis competition held at the Texas Section Society for Range Management annual meeting and won third place honors.
“Through my initial research, I have worked with the Texas A&M AgriLife Research and Extension Center at Stephenville to look at some of the phenolic compounds and condensed tannins in mesquite, and the concentrations are pretty negligible,” Burson said.
However, she said the U.S. Department of Agriculture Poisonous Plant Research Laboratory in Logan, Utah, has identified several alkaloids present in mesquite samples.
“I don’t know if I’m going to be able to figure out what specific compound causes browsing herbivores to avoid mesquite, but I’m hoping to gain a better idea of those present so we can develop a plan for its management,” Burson said.
One example of Burson’s findings guiding management can be seen in the response of the redberry juniper to prescribed fire.
“When redberry juniper resprouts after a fire, its concentration of terpenes is lower for a period of time,” Burson said. “In terms of management, this provides a window of time for ranchers to browse goats. The goats will select the new foliage, which helps ranchers manage the plant.”
Burson noted that although her research plots are within an exclosure to keep out livestock, she has seen evidence of other ungulates—namely white-tailed deer—taking advantage of the new sprouts.
Moving forward, Burson said she hopes to bridge the gap between basic chemical ecology and applied management to provide land managers with more tools to address vegetative competition on range lands.
“We can’t control all of the variables on the landscape that drive change, but we can increase our knowledge of how individual parts respond to these changes, alter our management strategies accordingly and build upon the resiliency of rangelands,” Burson said.
