Invasive grasses in South Texas rangelands: historical perspectives and future directions

摘要

South Texas is home to a high diversity of species due to its location at the confluence of subtropical, desert, and coastal ecoregions. 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 20th 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 King Ranch bluestem [Bothriochloa ischaemum(L.) Keng], Kleberg bluestem [Dichanthium annulatum(Forssk.) Stapf], Angelton bluestem [Dichanthium aristatum(Poir.) C.E. Hubbard], buffelgrass [Pennisetum ciliare(L.) Link], guineagrass [Urochloa maxima(Jacq.) R. Webster], Lehmann lovegrass (Eragrostis lehmannianaNees), and Bermudagrass [Cynodon dactylon(L.) Pers.], have escaped pasture cultivation. Additionally, the native grass tanglehead [Heteropogon contortus(L.) P. Beauv. ex Roem. & Schult.] has begun displaying invasive behaviors. The monoculture growth habit of these species simplifies vegetation structure, reduces biodiversity, and decreases habitat for many species of wildlife. These grasses also alter natural fire regimes and nutrient cycling. This landscape-level transformation of vegetation composition and structure requires monitoring to quantify and assess the spatial and temporal distributions of invasive species as a basis to inform management practices. Current advances in remote sensing technologies, such as very high spatial resolution coupled with daily satellite imagery and unmanned aerial vehicles, are providing tools for invasive vegetation monitoring. We provide a synthesis of the natural history of these grasses, including their introductions, an overview of remote sensing applications in South Texas, and recommendations for future management practices.