Multiscale Detection of Sulfur Cinquefoil Using Aerial Photography

We evaluated the effectiveness of natural color aerial photography as a tool to improve detection, monitoring, and mapping of sulfur cinquefoil (Potentilla recta L.) infestations. Sulfur cinquefoil is an exotic perennial plant invading interior Pacific Northwest rangelands. Because sulfur cinquefoil produces distinctive pale yellow flowers, we timed aerial photography for early July, when the plant was at peak bloom. Photography was collected at 3 spatial scales (1:3 000, 1:6 000, and 1:12 000). A grid with 250-m spacing was superimposed over photographs of the entire study area using geographic information systems. At each grid intersection point (n 1⁄4 80), we visually analyzed the photographs within a 404.7-m (0.1 acre) circular plot, recorded sulfur cinquefoil presence, and estimated sulfur cinquefoil percent cover. Sample points on the grid were then located in the field using a global positioning system. Field data collected at each point included sulfur cinquefoil presence, percent cover, and stem density; and total vegetation composition and percent cover by life form. Results indicate that the accuracy of detecting sulfur cinquefoil increased from small to large scale. At the 1:3 000 scale, sulfur cinquefoil presence was correctly identified in 76.9% of the sites, whereas at the 1:6 000 and 1:12 000 scales, infestations were identified in 67.9% and 59.1% of the sites, respectively. Low-density infestations (, 1% cover) were detected at all scales. Accuracy of percent cover estimates ranged from 33.8% to 38.0% across scales. Although tree canopy hindered detection, our results indicate that aerial photography can be used to detect sulfur cinquefoil infestations in open forests and rangelands in the Intermountain West.