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Research article - Peer-reviewed, 2009

Computer-aided calibration for visual estimation of vegetation cover

Torell, Gallegos Asa; Glimskar, Anders


QuestionWhat precision and accuracy of visual cover estimations can be achieved after repeated calibration with images of vegetation in which the true cover is known, and what factors influence the results?MethodsDigital images were created, in which the true cover of vegetation was digitally calculated. Fifteen observers made repeated estimates with immediate feedback on the true cover. The effects on precision and accuracy through time were evaluated with repeated proficiency tests. In a field trial, cover estimates, before and after calibration, were compared with point frequency data.ResultsEven a short time of calibration greatly improves precision and accuracy of the estimates, and can also reduce the influence of different backgrounds, aggregation patterns and experience. Experienced observers had a stronger tendency to underestimate the cover of narrow-leaved grasses before calibration. The field trial showed positive effects of computer-based calibration on precision, in that it led to considerably less between-observer variation for one of the two species groups.ConclusionsComputer-aided calibration of vegetation cover estimation is simple, self-explanatory and time-efficient, and might possibly reduce biases and drifts in estimate levels over time. Such calibration can also reduce between-observer variation in field estimates, at least for some species. However, the effects of calibration on estimations in the field must be further evaluated, especially for multilayered vegetation.


Environmental monitoring; observer error; plot inventory; vegetation cover

Published in

Journal of Vegetation Science
2009, Volume: 20, number: 6, pages: 973-983

    SLU Authors

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      Agricultural landscape

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