Assessment of Juniper Encroachment With The Use of Satellite Imagery and Geospatial Data |
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| Institution: | 1. Postdoctoral Research Associate, GIS Training and Research Center, Idaho State University, Pocatello, ID 83209, USA;2. Associate Professor, Department of Biological Sciences, Idaho State University, Pocatello, ID 83209, USA;1. Professor, Department of Natural Resource Management, SDSU, Brookings, SD 57007, USA;2. Soil Conservationist, USDA-NRCS, Madison, SD 57042, USA;3. Professor, Department of Plant Sciences, SDSU, Brookings, SD 57007, USA;4. Postdoctoral Researcher, Department of Plant Sciences, SDSU, Brookings, SD 57007, USA;5. Extension Cow-Calf Specialist, North Central Research and Outreach Center, University of Minnesota, Grand Rapids, MN 55744, USA.;1. Graduate Assistant, Department of Fish and Wildlife Sciences, University of Idaho, Moscow, ID 83844, USA,;2. Associate Professor, Department of Fish and Wildlife Sciences, University of Idaho, Moscow, ID 83844, USA;;3. Professor, Department of Forest, Rangeland and Fire Sciences, University of Idaho, Moscow, ID 83844, USA;;4. Associate Professor, Department of Statistical Science, University of Idaho, Moscow, ID 83844, USA;5. Wildlife Biologist, Bureau of Land Management, Dillon, MT 59725, USA.;1. Texas A&M AgriLife Research, 7887 U.S. Hwy. 87 N, San Angelo 76901, United States;2. Texas A&M University, Department of Animal Science, 133 Kleberg, College Station 77843, United States;1. Graduate Research Assistant, Range Science Program, School of Natural Resources, North Dakota State University, Fargo, ND 58105, USA.;2. Ecologist, USDA-ARS Fort Keogh Livestock and Range Research Laboratory, Miles City, MT 59301, USA.;3. Range Technician, USDA-ARS Fort Keogh Livestock and Range Research Laboratory, Miles City, MT 59301, USA. |
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| Abstract: | Juniper encroachment into otherwise treeless shrub lands and grasslands is one of the most pronounced environmental changes observed in rangelands of western North America in recent decades. Most studies on juniper change are conducted over small areas, although encroachment is occurring throughout regions. Whether changes in juniper cover can be assessed over large areas with the use of long-term satellite data is an important methodological question. A fundamental challenge in using satellite imagery to determine tree abundance in rangelands is that a mix of trees, sagebrush, and herbaceous cover types can occur within a given image pixel. Our objective was to determine if spectral mixture analysis could be used to estimate changes in Rocky Mountain juniper (Juniperus scopulorum Sarg) and Utah juniper (Juniperus osteosperma Torr.] Little) cover over 20 yr and 20000 ha in southeast Idaho with the use of Landsat imagery. We also examined the spatial patterns and variation of encroachment within our study area using Geographic Information Systems–based data sets of grazing use, land-cover types, and topography. Juniper cover determined from 15-cm-resolution digital aerial orthophotography was used to train and validate juniper presence/absence classification in 1985 and 2005 Landsat images. The two classified images were then compared to detect changes in juniper cover. The estimated rate of juniper encroachment over our study area was 22–30% between 1985 and 2005, consistent with previous ground-based studies. Moran’s I analysis indicated that juniper encroachment pattern was spatially random rather than clustered or uniform. Juniper encroachment was significantly greater in grazed areas (P = 0.02), and in particular in grazed shrub land cover type (P = 0.06), compared to ungrazed areas. Juniper encroachment was also greater on intermediate slopes (10–35% slopes) compared to steeper or flatter terrain, and encroachment was somewhat less on north-facing (P = 0.03) and more on west-facing (P = 0.02) slopes compared to other aspects. |
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