Accurate time- and cost-efficient mapping is central to successful rangeland invasive plant management. In this study sampling together with Inverse Distance Weighted (IDW) interpolation modeling was tested as a mapping alternative to expensive full-coverage delineation survey mapping methods. Our objective was to examine accuracies of presence/absence maps generated from 18 sampling strategies (3 sampling methods × 6 sample densities) using IDW. Invasive plant field survey maps with known accuracies were used to generate samples and to test interpolation results at 2 sites. Site 1 was approximately 6.0 km2, dominated by Russian knapweed (Acroptilon repens L.). Site 2, an upland area of approximately 13.5 km2, was dominated by spotted knapweed (Centaurea maculosa Lam). Sampling method × sample density combinations were gathered from field survey infestation maps using repeated computer-based sampling methods. IDW modeling was applied to each of the sample data sets. Accuracies of the IDW interpolation results were calculated by re-referencing field survey maps. We determined that sampling at density of 0.25% (about 1 point per ha) using a systematic sampling method was the preferred sampling strategy for both sites. This combination of sampling density and method yielded 85% accurate presence/absence maps. We conclude that sampling combined with IDW interpolation modeling can generate accurate invasive plant maps and is a potential alternative to current delineation survey methods.
Roberts, Elizabeth A.; Sheley, Roger L.; and Lawrence, Rick L.
"Using sampling and inverse distance weighted modeling for mapping invasive plants,"
Western North American Naturalist: Vol. 64
, Article 4.
Available at: http://scholarsarchive.byu.edu/wnan/vol64/iss3/4