Invasive grasses are a global problem that reduces biodiversity, changes ecosystem function, and can increase wildfire frequency and intensity. These grasses represent a widespread and costly problem in Texas and more broadly in rangelands, and pasturelands across the United States. Such grasses often outcompete and displace native grasses and forbs where they occur, reducing species richness and evenness across large swaths of habitat, often rendering the landscape less suitable for wildlife. The Invasive Species Research Lab at BFL is researching the ecology of these grasses in both native and introduced ranges to better inform approaches for the sustainable management of these species. We currently work with two focal invasive grasses; Buffelgrass and Guinea grass.
Cenchrus ciliaris (Buffelgrass)
Buffelgrass is a perennial African grass that began widespread introduction to Texas in the 1950s and has been heavily cultivated for improving livestock yields in semi-arid rangelands of South Texas. However, the same traits that make buffelgrass desirable for ranching also hinder natural ecosystem processes. Buffelgrass grows in dense stands that can shade out other native plants and usurp large amounts of water. By outcompeting native plants for space and water resources, this species often disrupts the native plant community, colonizing available space and creating nearly pure stands of buffelgrass in some cases. Buffelgrass is also adapted to frequent, hot fires, rendering burn treatments ineffective or even counterproductive, especially when large dense stands of buffelgrass ignite. While buffelgrass is still considered to be of benefit to many ranchers since it provides large stands of forage, the escape into natural brush communities hurts wildlife and native plant populations. A balanced approach is needed, for example by limiting seed production and escape into natural areas and reduction of excess biomass which presents a fire hazard.
Panicum maximum (Megathyrsus maximus) (Guinea grass)
Guinea grass is another perennial bunch grass native to Africa that grows in thick stands, outcompeting native plants and reducing diversity. Like buffelgrass, it is adapted to frequent fires and can even change fire regimes in areas where it becomes dominant by vastly increasing the available fuel load. It is also known to colonize open, recently disturbed areas, putting large areas of South Texas rangeland at risk of invasion. In South Texas, Guinea grass is commonly observed mostly around shrub clumps, or mottes, rather than in the grassy matrix between the trees. These shrub clumps are usually based around a central mesquite tree, a nitrogen-fixing species that also provides shade cover and higher soil moisture under the canopy, which are important factors in nutrient-poor, arid regions. The benefits of Guinea grass to ranching in South Texas is less clear, as it appears to be spreading quickly along highways across the south and into the San Antonio and Austin areas.
Our Invasive Grass Research Program
Our lab is interested in determining what functional and life history traits are associated with Guinea grass distribution in South Texas. We are studying how reproductive ecology drives patterns of invasion in South Texas. More broadly we are looking at how climate, geography, and genetics relate to current global distributions and future invasion potential. Understanding these patterns can inform management strategies that aim to protect native plant communities from Guinea grass invasion. We are using this knowledge towards applications in management, and aiding in the search for potential biological control. Brackenridge Field Lab leverages public and private partnerships with local and international partners in order to understand the basic biology and ecology of invasion. Specifically, we are testing the enemy release, and ecological release hypotheses to better understand what makes these two grasses so invasive.
We are further interested in ecological applications by understanding the ecological mechanisms underlying the success of buffelgrass and Guinea grass. Given their current and historical use as pasture grasses, our research must inform sustainable management strategies by ranchers and potential biological control.
For example, in one study we examine the effects that grazing treatments of different intensities can have on buffelgrass dominance and determining which patterns of disturbance encourage native plant diversity to recover. This study is being conducted in South Texas chaparral habitat in areas of frequent disturbance by cattle. We are also collaborating with a Kenyan research group at Mpala Research Center led by Dr. Dino Martins to understand buffelgrass' home range ecology and explore prospective biological control approaches. Here, we are experimentally removing natural enemies in buffelgrass’ native range in order to better understand which natural enemies hinder buffelgrass. If we can understand what these biotic and abiotic components are, we may simulate invasion in native habitats and better understand how grasses invade when introduced elsewhere.
Our Research Tools
We use ecological measurements in the field, plant functional and physiological measures in the field and in greenhouse experiments on BFL campus. We are cataloging arthropod species associated with both of our grasses species in Kenya and in Texas. We are developing novel tools in invasion ecology leveraging hyperspectral remotely sensed data on an uncrewed aerial vehicle (UAV). We also have several long-term studies across Kenya and in Texas that leverage camera traps, exclosures, and regular monitoring to understand the fundamental ecology of invasion and determine mechanisms of grass invasion.