Connecting the dots: Remote sensing of Glossy and Common Buckthorn (Frangula alnus and Rhamnus cathartica) in the Oak Openings Region of Northwest Ohio

Glossy and common buckthorn (Frangula alnus and Rhamnus cathartica) are invasive woody shrubs that formed dense monoculture thickets in the Oak Openings Region of NW Ohio. Conventional techniques of vegetation mapping are expensive and time-consuming. Thickets were identified using remotely sensed land surface phenology of buckthorn, that leafs out earlier and senesces later than native plant species. A tasseled-cap greenness index, which correlates with vegetation health and biomass, was calculated for 49 Landsat images across two time steps (2001-2006 and 2007-2011) to determine annual phenology. Areas of known thicket and aerial photography were used to classify buckthorn thicket. The satellite image classification showed a 37% increase in thicket extent (690 hectares to 945 hectares) between 2001-2011. P-plots were used to determine buckthorn thicket species composition and density. Sixty field sites were surveyed for presence/absence of thicket to determine accuracy and a kappa hat value of 0.73 was obtained. The classification image was used to model the spatial distribution of buckthorn in order to determine drivers causing monoculture thickets. A logistic regression was used against presence/absence of thicket as a function of the variables: height above river centerline, density of groundwater wells, and distance to agricultural sources. The model showed a pseudo-R2 value of 0.13 and predicted a 10-20% increase in likelihood of buckthorn thicket for each decrease of 30 cm elevation toward river center with a p-value of