Native woody juniper shrubs (Juniperus spp.) are expanding beyond their normal historical ranges as a result of wildfire suppression, prolonged drought, and reduced demand for juniper products such as fencing and building material. As juniper woodlands spread, typically from steep rocky slopes into adjacent foothill riparian and shrub-steppe communities, critical mule deer and greater sage-grouse habitat is reduced. Early stages of encroachment can be controlled with cost-effective mechanical treatments, while the only economical management strategy for denser canopy cover requires prescribed fire, which is difficult to implement and can lead to increased establishment of invasive grasses. As a result, the BLM Rawlins Field Office actively monitors juniper community expansion to identify early-stage areas suitable for mechanical treatment based on canopy cover and wildlife habitat needs.
BLM analysts used the Feature Analyst extension in Esri ArcMap 10.3.1 to conduct supervised classification of juniper canopy cover from the 2015 four-band, 0.5-m resolution, National Agricultural Imagery Program (NAIP) aerial photos acquired over 60,000 acres of BLM-managed rangeland near Saratoga, Wyoming. The study area comprised six separate management units. Representative juniper canopies were used to train the software to recognize the spectral signature and spatial pattern of juniper and classify the imagery for those traits. The river corridor was masked to avoid false positives from willow, alder, and cottonwood. The resulting juniper canopy cover maps provide a simple management tool for determining treatment priorities. For example, the blue and green pixels in the classified image (C) represent low canopy cover areas that are suitable for mechanical treatment.
Geographic Information System (GIS) products derived from classification of (A) the original 2015 NAIP imagery included (B) a pixel-level juniper canopy polygon layer and (C) a layer showing juniper canopy cover aggregated by acre unit.