Digital Photography: Reduced Investigator Variation in Visual Obstruction Measurements for Southern Tallgrass Prairie |
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| Affiliation: | 1. Graduate Student, Department of Natural Resource Ecology and Management, Oklahoma State University, Stillwater, OK 50010;2. Associate Professor, Department of Natural Resource Ecology and Management, Oklahoma State University, Stillwater, OK 50010;3. Professor and Chair, Department of Natural Resource Ecology and Management, Iowa State University, Ames, IA 50010;4. Research Specialist, Department of Animal and Range Sciences, North Dakota State University, Fargo, ND 58105;5. Professor, Department of Natural Resource Ecology and Management, Oklahoma State University, Stillwater, OK 74078;1. Supervisory Research Ecologist, U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center, 970 Lusk St., Boise, ID 83706, USA;2. Ecologist, U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center, 970 Lusk St., Boise, ID 83706, USA;3. Assessment, Inventory and Monitoring Lead, Bureau of Land Management, 1849 C Street NW, Washington, DC 20240, USA;1. Natural Resource Management, North Dakota State University, Fargo, ND, USA;2. Range Science, Hettinger Research Extension Center, PO Box 1377, Hettinger, ND 58639, USA;3. Range Science, North Dakota State University, 202 Hultz Hall, 1300 Albrecht Boulevard, Fargo, ND 58105, USA;4. Central Grasslands Research Extension Center, 4824 48th Avenue, Streeter, ND 58483, USA;5. Plant Sciences, North Dakota State University, Loftsgard Hall 270A, 1360 Albrecht Boulevard, Fargo, ND 58102, USA;1. Northern Great Plains Research Laboratory, Agricultural Research Service, US Department of Agriculture (USDA), Mandan, ND 58554, USA;2. Natural Resource Conservation Service (Retired), USDA, Bismarck, ND 58502, USA |
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| Abstract: | Landscapes with structural heterogeneity or patchiness can support diverse and stable wildlife populations. Visual obstruction methods (i.e., Robel pole and Nudd's coverboard) are common and useful techniques for quantifying vegetation structure; however, both rely on ocular estimations, which can be highly variable between observers. Our objectives were to 1) compare measurement and observer variation for visual obstruction among the two standard methods and the digital image method we developed using a digital camera; and 2) compare the performance of the Robel pole and digital image to estimate standing crop. The mean variation across the five observers using the digital image method (6.8%) was significantly lower (P < 0.05) than both the Nudds' coverboard (32.1%) and the Robel pole (52.2). There were no significant differences among locations for the digital image method; however, there were for both the Robel pole and Nudds' cover board (P < 0.05). The digital image method provided a better estimate of standing crop (r2 = 0.89) compared to the Robel pole (r2 = 0.68), accounting for 21% more of the observed variation in biomass. Long-term research programs that utilize seasonal field technicians to quantify habitat structure with a visual obstruction method could benefit from implementing use of the digital image method we developed. The low measurement error observed with this technique relative to the more traditional methods compared in this study might limit year-to-year and within-year variability of habitat structure data collected by numerous technicians with a high annual turnover. |
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