RESULTS AND DISCUSSION 



Data Base 



Sixty-six of the approximately 200 major mountain ranges in the Great Basin were 

 visited and vegetation data were obtained at 482 plots (table 1 and fig. 1). These 

 data, along with additional observations on vegetation boundaries, provided ground 

 truth data for the mapping phase. 



Type Map 



A detailed map of the distribution of the Great Basin pinyon- juniper woodlands is 

 provided in figure 2. This map is the most detailed and field-verified of any yet 

 available for the pinyon- juniper vegetation type. The map should have many uses in 

 inventory, planning, management, research, and teaching. 



There is not complete congruence of the woodland boundaries shown on this map 

 (fig. 2) with the lower boundaries of mountain ranges shown on the topographic-based 

 map (fig. 1). The lack of congruence results from the woodland n6t occupying perfect 

 belts around every Great Basin mountain range. In the northern Great Basin, pinyon- 

 juniper woodland belts are narrower or lacking altogether on northern exposures. The 

 woodland belt frequently diminishes on southern exposures in the southern Great Basin. 

 East and west-facing woodland belts are not always at the same elevation or of the 

 same width. In southwestern Utah and adjacent Nevada, valley bottoms are at higher 

 elevations and a distinct change occurs from mountain-valley topography to rolling 

 terrain. In these areas woodlands become continuous between ridges. Details of these 

 differences in woodland and mountain range boundaries and their possible causes have 

 already been discussed in West and others (1978) . 



Comparison of the location of pinyon- juniper boundaries on the map with boundary 

 locations noted during field research allows us to estimate that less than 5 percent 

 error exists; i.e., less that 5 percent of the boundary locations are delinated incor- 

 rectly from the LANDSAT-1 imagery. If areas of pinyon- juniper woodland were continuous, 

 densities as low as 41 trees per hectare were visible on LANDSAT-1 color-infrared 

 imagery. Areas of pinyon- juniper woodland as small as 62 acres (25 ha) were visible if 

 there were at least 73 trees per hectare. A discontinuous area of pinyon- juniper having 

 trees only on the lower slopes of many close ridges showed sufficient reflectance to be 

 identified only when tree density exceeded 118 trees per hectare. Generally, a pinyon- 

 juniper community larger than 25 ha with a density of about 75 trees per hectare can be 

 identified on LANDSAT-1 color-infrared imagery. 



The area of pinyon- juniper woodlands within the study area boundaries was 

 estimated using the dot grid technique (table 2). This estimate is more that 4 

 million acres less than an estimate derived from planimetering the major forest-type 

 overlay map (9-W) in Little (1971). This difference could be due to Little's inclu- 

 sion of some higher mountain centers in his map and/or to his extension of the 

 pinyon- juniper woodland into considerably more open juniper stands at the base of 

 these mountains. 



The differences betweeen our acreages and those available from the map on page 

 111 of Cronquist and others (1972) are less, probably due to Cronquist's distinction 

 of the major mountain centers as "montane zone." The two maps cannot be compared 

 precisely because of the extension of our study area further south than that given in 

 Cronquist and others (1972). The map produced in this study provides more detail on 

 the pinyon- juniper type boundary than theirs because of its larger scale. 



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