Pinyon-juniper stem-mapped GIS dataset: upper and lower treelines of Toiyabe range, Nevada (USA)
Data type: multipoint shape file (ESRI format) of 20 sample plots
Sampling design: 20 sample plots (10 upper treelines + 10 lower treelines) along the Toiyabe range of Nevada, US
Data sources and methods: on-screen photointerpretation of high-resolution (30 cm) aerial photographs (Bing Maps Microsoft Virtual Earth; year 2012) available from the ArcGIS Online service (ESRI, 2012). The approach consists of a manual segmentation of the image at a map scale ranging between 1:400 and 1:600 to identify tree crown polygons, and subsequently the canopy cover and the centroid of each detected tree. The minimum mapping unit (MMU) adopted in the image analysis was 0.78 m2 corresponding to a crown radius of at least 0.5 m.
Validation: The 20 vector maps resulting from this process were validated through accuracy assessment by ground control plots (GCPs) collected in the field during June and July of 2015. The accuracy of the image classification was obtained by calculating the number of correctly classified trees (matches =M), trees detected in the image but absent on the field (false presence = FP) and trees present on the field but not detected on the image (false absence = FA). The final accuracy, calculated on a total of 104 ground control points (GCPs) was 83% total matches, 10% false absences and 7% false presences.
