Aerial assessment of leafy spurge (Euphorbia esula L.) on Idaho’s Deep Fire Burn

Abstract

High-resolution aerial surveys are a highly effective means for monitoring new and dispersed invasive-species infestations across extensive areas of wildland. Invasive species constitute a leading threat to native vegetation in wildland settings. Monitoring and controlling these species are essential actions to preserving native-plant community integrity and historic wildland character. Infestations continue to increase. Monitoring with conventional ground or lower-resolution aerial data may be problematic as these tools are of questionable value for detecting small or dispersed weed populations. In July 2006, we conducted a dual-camera aerial survey acquiring 1- and 10-mm ground sample distance (GSD) imagery in the Medicine Lodge watershed in eastern Idaho. The survey included most of the 2003 Deep Fire Burn. Survey data were used to determine leafy spurge (Euphorbia esula L. [Euphorbiaceae]) distribution on burned and unburned lands and to relate spurge distribution to ecosystem structure, associated vegetation, and control efforts. Leafy spurge was detected in 10% of 10-mm GSD samples versus 8% of 1-mm GSD samples. We conclude that 10-mm GSD is best for detecting leafy spurge because it optimizes the balance between resolution and field-of-view. Litter was about 4% greater where spurge was present than where it was not, and spurge occurrence was associated with significant decreases in cover of native grasses, forbs, and sagebrush (Artemisia spp. L. [Asteraceae]). Leafy spurge proximity to water was higher than a random distribution would predict.