Image-based monitoring to measure ecological change in rangelands

Authors: Booth, D; Cox, Samuel

Submitted to: Frontiers in Ecology and the Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/11/2007
Publication Date: 5/4/2008
Citation: Booth, D.T., Cox, S.E. 2008. Image-based monitoring to measure ecological change in rangelands. Frontiers in Ecology and the Environment 6(4):185-190.

Interpretive Summary: Most conventional methods for assessing ecological “health” are labor intensive, expensive, and therefore unsuited for extensive areas; judgment-based assessments are faster but vary with the stresses and biases of individuals. Digital camera monitoring and associated computer image-analysis are advancements that may replace conventional monitoring. We tested aerial and ground digital photography with manual and automated analyses for detecting ground-cover differences in shortgrass-prairie pastures stocked at different rates for 3 years. Vegetative cover changes due to grazing were detected from the air (100-m above ground level or AGL) and from the ground (2-m AGL), suggesting that either method has the potential to detect change in key indicators such as bare ground. We conclude that image-based monitoring is cost effective for extensive area and capable of detecting ecologically important changes.

Technical Abstract: High-resolution image-based methods can increase the speed and accuracy of ecological monitoring while reducing monitoring costs. We evaluated the efficacy of systematic aerial and ground sampling protocols to detect stocking-rate differences across 130 ha of shortgrass prairie. Manual and automated image-analysis methods were compared for both aerial and ground data. Vegetative cover changes due to grazing were detectable from 1-mm ground sample distance aerial photography (30,000 times the resolution of Landsat) with as few as 30 samples yielding enough data to predict bare ground within ±5%. We found poor agreement between automated and manual image-analysis methods; but high agreement between manual analyses of imagery from the air (100-m above ground level or AGL) and from the ground (2-m AGL), suggesting that either method has the potential to detect change in key indicators such as bare ground. Costs between ground and aerial methods differed markedly and we infer that ground imagery is the most cost-effective choice for single areas of 200 ha or smaller with easy access.