Delineation of Vegetation in Clark County Using Satellite Imagery

Of the 5.1 million acres of land in Clark County, about 4.6 million acres (approximately 90 percent) are administered by six Federal agencies, including the Bureau of Land Management (BLM), National Park Service, U.S. Fish and Wildlife Service, USDA Forest Service, U.S. Air Force (including Nellis Air Force Base and Nellis Air Force Range), and U.S. Trust Lands. Federal land management agencies in Clark County must manage the land to protect natural resources, while providing for the needs of a rapidly growing population. Many decisions which lead to activities or development on public land and which may affect natural resources are driven by population growth (Clark County is one of the fastest-growing areas in the country, with more than 5,000 people moving to the county each month.) When making land management decisions, managers need to evaluate the potential impact to natural resources, based on the best available data. Data that would be useful to land managers during the decision making process include detailed delineation and classification of plant communities according to composition and density, delineation of phreatophyte areas, and quantification of phreatophytic water use.

Objectives

Acquire high resolution geospatially rectified remotely sensed data, use spectral analysis to delineate vegetation according to composition and density, use geographic information systems software to produce vegetation map overlays, and determine rates and volumes of consumptive water use by phreatophytic vegetation.

Strategy and Approach

The USGS Nevada Water Science Center (NVWSC) will establish approximately 200 vegetation plots. Plots will be located in selected areas of Clark County in vegetated areas where the plant cover is representative of plant communities of a composition and density that can be uniquely identified by spectral analysis of high resolution satellite imagery. BLM will purchase geospatially rectified high-resolution satellite-imagery consisting of multi-spectral and panchromatic bands. NVWSC will use image processing software to apply atmospheric corrections, perform independent spectral analysis, classify vegetation into identifiable groups for each scene according to plant composition and density, verify vegetation classification, and will create polygon coverage of vegetation groups.  A mosaic of polygon coverage will be used to produce three digital map overlays for selected areas of Clark County showing vegetation groups, vegetation densities, and phreatophyte areas. Annual evapotranspiration rates and consumptive use of groundwater for areas of phreatophytes that can be individually identified either with remote sensing imagery or by site visits will be estimated.

Relevance and Benefits

The delineation of plant communities according to composition and density, delineation of phreatophyte areas, and quantification of phreatophytic water use will provide data that federal land mangers can use to identify areas that (1) may have sensitive plant species that require protection, (2) may be critical wildlife habitat, (3) have high wildfire risk, and (4) critical plant and wildlife habitat rely on for their water supply. This data also will provide a baseline for monitoring changes to plant communities’ composition and/or density and vegetative land cover data that can be part of flood risk assessment. A geographic information systems map consisting of separate overlays displaying vegetation and water-use data can be a tool to support land management decisions.