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1 September 2007 Large-scale Aerial Images Capture Details of Invasive Plant Populations
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Satellite and high-altitude aerial remote sensing have been used to measure dense infestations of invasive weeds over very large areas but have limited resolution and cannot be used to detect sparsely distributed weeds. Ground-based methods have provided detailed measurements of invasive weeds but can measure only limited areas. Here we test a novel approach that uses a lightweight airplane, flying at 72 km ṡ h−1 and 100-m altitude, to rapidly collect high-resolution images over relatively large areas. We obtained 1 987 images, each representing 48.5 m2 of mixed-grass prairie with 2-mm resolution (ground sample distance). From these images we were able to reliably measure small patches and even individual plants of the invasive forb Dalmatian toadflax (Linaria dalmatica [L.] P. Mill.). Ground-based measurements of aboveground toadflax biomass were highly correlated (R2 > 0.93) with point-intercept and visual-estimate cover measurements from aerial images. The time required to analyze images ranged from 4 to 45 seconds for presence/absence data and from 1 to 6 minutes for cover data. Toadflax was present in 795 of 1 987 images but exceeded 1% cover in only 99 images. Given the observed variation among images in toadflax cover, at least 400 images were needed to precisely estimate the mean toadflax cover of 0.2%. These results suggest that such high-resolution aerial imagery could be used to obtain detailed measurements of many invasive weed populations. It may be most useful for identifying incipient weed infestations and expanding the scale at which population-level attributes of weed populations can be effectively measured.

Received: 14 December 2006; Accepted: 27 May 2007; Published: 1 September 2007

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