Remote Sensing of Biological Soil Crusts

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Biological soil crusts (biocrusts, photoautotrophic soil surface communities comprised of cyanobacteria, algae, bryophytes, lichens, and fungi, occur in drylands globally where they contribute to ecosystem functioning by increasing soil stability, reducing dust emissions, and modifying soil resource availability (e.g., water, nutrients) (Fig 1.3.1). Despite increasing recognition and interest in the global extent and functional importance of biocrusts, determining the spatial extent and condition of biocrusts across landscapes continues to present considerable challenges to scientists and land managers making it difficult to quantify biocrust contributions to ecosystem functioning at larger spatial scales. However, given that biocrust biomass and biological activity is typically concentrated and visible in the uppermost millimeters of the soil surface, remote sensing offers promising opportunities to detect and characterize biocrust communities, differentiate among biocrust community types, and monitor changes in biocrust distribution across dryland landscapes globally.

Biocrusts grow in patches, cover vast expanses of rugged terrain, and are vulnerable to physical disturbance associated with ground-based mapping techniques.  Therefore, small Unmanned Aerial Systems (UAS) provide an ideal platform to provide detailed mapping of these fragile communities (Figure 1.3.2.). For this project we are using low-cost UASs to collect high-resolution (less than 1-cm) images to map biocrust, soils and vegetation cover. We established 80 plots across 10 field sites south of Canyonlands National Park in southeastern Utah, and measured cover and composition of biocrusts (and herbaceous plants (Figure 1.3.3). that were used to train and validate UAS image classifications (Figure 1.3.4). Results from this study will aid scientists and land managers in mapping and monitoring biocrust condition and extent across drylands, which may increase our ability to monitor biocrust function by linking biocrust contributions to ecosystem processes at larger spatial scales, and set future targets for dryland conservation and restoration.

Future work: Field monitoring plots and UAS imagery will be used to scale up biocrust information over the larger landscape using high resolution WorldView-3 satellite data (31-cm panchromatic resolution, 1.24-m multispectral, and 3.7-m shortwave infrared), and moderate-resolution Sentinel and Landsat satellites. 

Photo of soil crust

Figure 1.3.1. Ground photographs depicting a layer of dark biocrust in a pinyon juniper study site in southeastern Utah. 

(Credit: Miguel Villarreal, USGS. Public domain.)

 

A photo of pilots planning flight paths

Figure 1.3.2. USGS and Department of Interior UAS pilots plan a flight near Canyonland, Utah. 

(Credit: Miguel Villarreal, USGS. Public domain.)

A photo of a USGS collecting biocrust data

Figure 1.3.3. Collecting biocrust cover data to train and verify the UAS image classifications.

(Credit: Miguel Villarreal, USGS. Caroline Havrilla's image used with permission)

 

A graphic depicting an image classification

Figure 1.3.4. Example map showing UAS image (A) and resulting image classification (B). 

(Public domain.)

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