A remote sensing approach to detecting Old World Bluestems in South Texas

Historical overgrazing of South Texas rangelands transformed the savanna and prairie to a landscape dominated by woody plants and shrubs interspersed with low seral grass species and bare ground. During the first half of the twentieth century, exotic grass species, coupled with the application of industrial agricultural practices, appeared to be the future of forage production in South Texas and elsewhere. Several of these exotic species, namely the Old World bluestems [(Bothriochloa ischaemum), Kleberg bluestem (Dichanthium annulatum), and Angelton bluestem (Dichanthium aristatum)], buffelgrass (Pennisetum ciliare), guineagrass (Megathyrsus maximus), Lehmann lovegrass (Eragrostis lehmanniana), and bermudagrass (Cynodon dactylon) have escaped pasture cultivation. Additionally, the native grass tanglehead (Heteropogon contortus) has begun displaying invasive behaviors. These species form thick monocultures that simplify vegetation structure, reduce biodiversity, and decrease habitats for many species of wildlife. I determined the feasibility of using remotely sensed data to determine large scale Old World bluestem distribution on study sites in Kingsville and Premont, Texas. I assessed the performance of pixel-based classifications of cover types for National Agriculture Imagery Program (NAIP; 1-m resolution) and Sentinel-2 (10-m) imagery and evaluated the effect of classification resolution with landscape metrics. The NAIP imagery more accurately classified the true distribution of Old World bluestem cover. The lower resolution Sentinel-2 classifications failed to classify small patches and instead aggregated patches