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Title: Aerial Assessment of Leafy Spurge (Euphorbia esula L.) on Idaho's Deep Fire Burn

item Booth, D
item Cox, Samuel
item Teel, Deena

Submitted to: Native Plant Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2010
Publication Date: 7/1/2010
Citation: Booth, D.T., Cox, S.E., Teel, D. 2010. Aerial Assessment of Leafy Spurge (Euphorbia esula L.) on Idaho's Deep Fire Burn. Native Plant Journal 11(3):327-339.

Interpretive Summary: Aggressive weeds are replacing native plants on wildlands (national and state parks, forests, rangelands and etc.), but finding and removing small wildland weed populations is problematic—as is weed detection with aerial and space imagery where resolutions are too coarse to show small weed groups of weeds. We simultaneously triggered 2 digital cameras at 2 levels of high-resolution, to obtain images for 1,383 intermittent locations over 85 square miles of eastern Idaho wildland; and, we used the images to measure leafy spurge distribution and affect on native plants. Leafy spurge was detected in 8 and 10% of our high and low resolution images, respectively, and those images show leafy spurge occurrence to be associated with measureable decreases in native grasses, forbs, and sagebrush and that in particular, it had replaced native plants around rock outcrops and near streams. High-resolution aerial surveys are useful for detecting new and dispersed weed infestations on wildland and should be used to look for weeds growing away from roads.

Technical Abstract: 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 since 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. Leafy spurge remains a significant problem on the study area but, high-resolution aerial surveys, such as described in this report, are an effective means for monitoring new and dispersed infestations across this, and other extensive areas of wildland.