Separating Crested Wheatgrass Using Field Hyperspectral Data in the Native Prairie of Southwestern Saskatchewan

Crested Wheatgrass (Agropyron cristatum) is an introduced invasive grass species in North American grasslands. It was initially seeded to increase the grazing duration, but is now threatening native grassland biodiversity. Effective monitoring of Crested Wheat-grass requires robust remote sensing methods, yet prior studies relying on multispectral satellite data have faced limitations due to spectral similarity with co-occurring vegetation. In this study, we investigated which biophysical and spectral properties (hyperspectral and simulated multispectral) distinguish Crested Wheatgrass from native grasses. We further assessed whether spectral indices, linked to biophysical traits, could distinguish Crested Wheatgrass from native grasses. We collected field data of hyperspectral reflectance, leaf area index (LAI), biomass, and vegetation cover. We found that the differences between Creased Wheatgrass and native grasses are significant for many biophysical properties and spectral features. Grass cover, height, LAI, and biomass (grass, total and dead) are much higher for Crested Wheat grass sites, while bare ground cover is lower compared to native grasses. Hyperspectral data revealed distinct lower reflectance for Crested Wheat grass in visible and shortwave infrared regions (SWIR) compared to native grasses, which might be driven by differences in photosynthetic pigments and moisture content. SWIR spectral indices for hyperspectral data, SWIR and visible spectral indices for simulated Sentinel-2A data, and visible spectral indices for PlanetScope SuperDove data discriminated Crested Wheatgrass from native grasses. These findings advance invasive grass monitoring by shifting the focus from phenology to biophysical properties based detection, supporting management of Crested Wheatgrass and restoration of native grassland ecosystems.