Invasive buffelgrass (Pennisetum ciliare) spreads easily in the Sonoran Desert ecosystem, where it forms a continuous fuel layer that carries fire across the landscape, threatening native flora and fauna species. Current management of buffelgrass in Saguaro National Park (SNP) includes the targeted application of herbicide, which is most effective when the grass is photosynthetically active. The erratic, localized rain events characteristic of the Sonoran Desert complicate treatment by making it difficult to predict when buffelgrass will be green and therefore suited to treatment.
In collaboration with National Park Service (NPS) ecologists, USGS scientists are assisting buffelgrass eradication efforts by developing remote-sensing-based strategies to identify infestation locations and optimal timing of herbicide treatment. A prototype web-based application analyzes recent precipitation data to highlight when and where buffelgrass green-up thresholds have been reached. It also displays satellite-detected changes in greenness via normalized difference vegetation index (NDVI) values to show where vegetation green-up has occurred. To map where invasive buffelgrass is present, Climate Landscape Response (CLaRe) metrics, which leverage the correlation between precipitation amounts and NDVI, are used in classification algorithms. Nascent buffelgrass populations are detected by analyzing temporal patterns of climate-normalized CLaRe metrics across years.
Local partners and land managers involved in buffelgrass control efforts are providing feedback to guide the development of the application’s design and content. The most useful features will be assimilated into the USA-NPN (National Phenology Network) suite of online phenological tools, which provide regional- to national-scale information to help guide science-based resource management actions.
Examples of (left) a Sonoran Desert landscape showing the characteristic arrangement of clumps of native vegetation separated by bare ground; and (right) a Sonoran Desert landscape that has been invaded by buffelgrass, which fills in the open spaces with fine fuels that can carry fire across the landscape. (Photo Credit: Aaryn Olsson, The University of Arizona)