MAPPING THE INVASIVE SPECIES LEAFY SPURGE (EUPHORBIA ESULA) IN THEODORE ROOSEVELT NATIONAL PARK USING FIELD MEASUREMENTS OF VEGETATION SPECTRA AND IMAGING SPECTROSCOPY DATA

The invasive species leafy spurge (Euphorbia esula) is a major resource management challenge in Theodore Roosevelt National Park, North Dakota, USA. Leafy spurge has displaced native vegetation in riparian areas, grasslands, and ridges in the park. This paper reports on the successful application of spectroscopic methods of remote sensing to identify the spectral signature of leafy spurge and map its distribution in images collected by the Compact Airborne Spectrographic Imager (CASI) on June 28, 2000. Field measurements of leafy spurge and native vegetation communities were made using an ASD Full Range field spectrometer. These measurements were convolved to the sampling and bandpass characteristics of the CASI data. The original and convolved spectra reveal that the reflectance signature of leafy spurge can be discriminated from the reflectance signatures of other vegetation in the park. Several methods were applied to atmospherically-corrected CASI data to map leafy spurge, including: 1) direct comparison of field measured vegetation spectra to remotely-sensed CASI spectra using the chlorophyll absorption feature and a feature fitting algorithm; and 2) the spectral angle mapper (SAM) algorithm applied to minimum noise fraction (MNF) bands. Both approaches were successful at detecting leafy spurge in CASI images. These maps of leafy spurge, derived from spectroscopic remote sensing methods, were verified by field surveys and comparison to maps of leafy spurge derived from air photos. The maps derived from CASI indicate that biological control methods using flea beetles (Aphthona nigriscutis and A. lacertosa) have been successful at reducing the aboveground cover of leafy spurge.