In Texas, mesquite trees are as common as football, thunderstorms and hot summer nights. It is a staple of outdoor cooking and prevalent in almost every part of the state. But, for land managers, the spread of honey mesquite, a native and prevalent species, is an issue, as is the non-native yellow bluestem, a grass species native to eastern Europe and Asia that has been spreading throughout the southern United States over the last few decades.

Together, these two species are a threat to maintaining rangeland diversity and productivity. Controlling these two species, however, has been difficult. Hopefully, thanks to research by a team from Texas Tech's Department of Natural Resources Management, rangeland managers may now have a method to get a leg up on controlling the spread of honey mesquite and yellow bluestem.

"Rangeland managers are interested in eradicating both species in order to maintain rangeland diversity and productivity," said Carlos Portillo-Quintero, an associate professor with Tech's Department of Natural Resources Management. "However, their suppression is a site-level process implemented by the rangeland manager that involves regular mechanical or chemical treatments."

Former master's student Matthew Jackson, who now serves as the Geographic Information System/Remote Sensing Manager for the Memorial Park Conservatory in Houston, led a project along with Portillo-Quintero and Robert Cox, an associate professor and President's Excellence in Teaching Professor in the Department of Natural Resources Management, using unmanned aerial vehicles (UAV) to study the effects of and the ability to detect and map mesquite and bluestem growth.

The results could help rangeland managers better control the spread and effectiveness of eradication techniques. "At Texas Tech's Geospatial Technologies Laboratory, we have been using low-cost commercial UAVs to inspect and map ecological features in different types of landscapes around Texas," Portillo-Quintero said. "The objective was to generate knowledge on the best practices that rangeland managers and contractors can apply when using this type of mapping technology."

Joining Jackson, Portillo-Quintero and Cox on the project were Tech's Department of Plant and Soil Science Chairman Glen Ritchie, Natural Resources Management graduate students Mark Johnson and Mukti Subedi, and State University of New York-Potsdam geology assistant professor Kamal Humagain. The research was conducted at Tech's College of Agricultural Sciences & Natural Resources native rangeland site in Lubbock County, designed for studies in ecological and range management research.

In order to best determine how widely and quickly the honey mesquite and yellow bluestem spread, the Texas Tech researchers utilized a DJI Phantom 3 Pro UAV equipped with a 12-megapixel camera. The UAV would conduct one-hour flights using the Pix 4D Capture mobile application on an iPhone to create flight plans and automatically fly the UAV.

Portillo-Quintero said this setup was used because of its popularity and low cost so that land managers could affordably use the same setup if they wanted to conduct the same flights. Flights were conducted and data was collected at altitudes of 30, 60 and 100 meters. The UAV and camera were able to capture high-resolution imagery and elevations over the entire rangeland site, and an image classification process using artificial intelligence algorithms and other classifiers were used to detect the honey mesquite and yellow bluestem plants.

"In order to be detectable, mesquite shrubs would have to be juveniles or adult plants," Portillo-Quintero said. "Yellow bluestem would have to be adults. The influence of the soil background and its similarity to other species of grasses makes it more difficult to accurately detect."

Of all the flights made by the UAV over all types of seasons, it was determined the flights at 100 meters conducted during the spring were the most effective – with more than 80% accuracy – for mapping mesquite canopies based on reflection values and image segmentation information. However, for yellow bluestem, the mapping accuracy at 100 meters was extremely low, less than 20%.

"Using the recommendations from our work, it is possible to map the distribution of the mesquite trees and plan ahead for their removal with high accuracy," Portillo-Quintero said. "It is now much easier for technicians and investigators to perform such assessment with less cost and effort in a shorter time."

Contractors in charge of managing a mesquite invasion, for example, can rely on UAV-based measurements to have a better sense of the amount of materials and equipment needed for its removal, he said. A before-and after-assessment also can show the effectiveness of their removal techniques to the landowner.

Given the success of this project, Portillo-Quintero said the next step would be continuing this line of research using UAVs and multispectral cameras, potentially investigating other remotely sensed data such as light detection and ranging (lidar), or using laser light to illuminate and measure the reflection off an object. Portillo-Quintero said Jackson has begun implementing these techniques for tree-cover mapping and urban ecology research in his position at the Memorial Park Conservatory.

"Identifying and monitoring juvenile and adult plants while they colonize new areas across the landscape helps prioritize locations for treatment," Portillo-Quintero said. "These are all money- and time-consuming activities."

CONTACT: Carlos Portillo-Quintero, Associate Professor, Department of Natural Resources Management, Texas Tech University at (806) 834- 7309 or carlos.portillo@ttu.edu

0918NM20 / Editor's Note: To see the full text version of George Watson's news article, please click here