DEM Development from Ground-Based LiDAR Data: A Method to Remove Non-Surface Objects

Topography and land cover characteristics can have significant effects on infiltration, runoff, and erosion processes on watersheds. The ability to model the timing and routing of surface water and erosion is affected by the resolution of the digital elevation model (DEM). High resolution ground-based Light Detecting and Ranging (LiDAR) technology can be used to collect detailed topographic and land cover characteristic data. In this study, a method was developed to remove vegetation from ground-based LiDAR data to create high resolution DEMs. Research was conducted on intensively studied rainfall–runoff plots on the USDA-ARS Walnut Gulch Experimental Watershed in Southeast Arizona. LiDAR data were used to generate 1 cm resolution digital surface models (DSM) for 5 plots. DSMs created directly from LiDAR data contain non-surface objects such as vegetation cover. A vegetation removal method was developed which used a slope threshold and a focal mean filter method to remove vegetation and create bare earth DEMs. The method was validated on a synthetic plot, where rocks and vegetation were added incrementally. Results of the validation showed a vertical error of ±7.5 mm in the final DEM

Comparing Vegetation Monitoring Methods in Shrublands: How Valuable is Grant’s Method in Shrub Communities?

Faced with managing extensive rangelands, land managers need reliable monitoring methods. Grant and others (2004) proposed a monitoring method that uses a floristic classification of dominant vegetation and assesses species frequency. The method was developed in native grass prairies with limited woody vegetation and is designed to provide more efficient repetitive monitoring. Our objective for this study was to determine if Grant’s method is useful in shrubland systems for a newly implemented baseline inventory and monitoring program. We conducted a study to compare Grant’s method and its efficacy to more commonly used line-point intercept in grass and shrub alliances at Brown’s Park National Wildlife Refuge, Colorado. In the summer of 2007 we conducted baseline inventory of vegetation characteristics on 39 permanent bottomland plots in six pre-determined grass and shrub vegetation alliances on the refuge. Within each plot, we monitored vegetation with line-point intercept and Grant’s method on three 50 m line transects. We compare data collected using these methods from a grassland (smooth brome dominated) and a shrubland (greasewood dominated) alliance. Results of this study indicate that data collected using Grant’s method is more variable than line-point intercept data in shrub systems. Bare ground was detected less using Grant’s than line-point intercept; however, Grant’s detected more herbaceous and invasive species overall than did the line-point intercept method. A complementary use of the methods for long-term monitoring is recommended that accommodates tradeoffs between incorporating detail versus efficiency of data collection efforts

Partitioning Evapotranspiration in Semiarid Grassland and Shrubland Ecosystems Using Diurnal Surface Temperature Variation

The encroachment of woody plants in grasslands across the Western U.S. will affect soil water availability by altering the contributions of evaporation (E) and transpiration (T) to total evapotranspiration (ET). To study this phenomenon, a network of flux stations is in place to measure ET in grass- and shrub-dominated ecosystems throughout the Western U.S. A method is described and tested here to partition the daily measurements of ET into E and T based on diurnal surface temperature variations of the soil and standard energy balance theory. The difference between the mid-afternoon and pre-dawn soil surface temperature, termed Apparent Thermal Inertia (I(sub A)), was used to identify days when E was negligible, and thus, ET=T. For other days, a three-step procedure based on energy balance equations was used to estimate Qe contributions of daily E and T to total daily ET. The method was tested at Walnut Gulch Experimental Watershed in southeast Arizona based on Bowen ratio estimates of ET and continuous measurements of surface temperature with an infrared thermometer (IRT) from 2004- 2005, and a second dataset of Bowen ratio, IRT and stem-flow gage measurements in 2003. Results showed that reasonable estimates of daily T were obtained for a multi-year period with ease of operation and minimal cost. With known season-long daily T, E and ET, it is possible to determine the soil water availability associated with grass- and shrub-dominated sites and better understand the hydrologic impact of regional woody plant encroachment

Sagebrush-Obligate Passerine Response to Ecological Site Characteristics

Adoption of ecological sites as monitoring and management units by a variety of land users has prompted discussion of their benefits for wildlife habitat management. Density and occurrence of shrub-steppe passerines are often related to key habitat characteristics such as plant species composition, cover, and structure. Until recently, ecological sites have not been tested as units for monitoring and management of passerines. We conducted a study implementing ecological sites as management units and used passerines as indicators of potential use of these sites. Ecological site characteristics and three sagebrush-obligate passerines were quantified on ecological sites at and near Browns Park National Wildlife Refuge in Colorado. In 2006 and 2007, we surveyed passerines and site characteristics using standard techniques within 101, 100-m radius plots. Density of Brewer’s sparrow (Spizella breweri) and occurrence of Brewer’s sparrow, sage sparrow (Amphispiza belli), and sage thrasher (Oreoscoptes montanu) were estimated for six ecological sites and then related to site characteristics. For example, Brewer’s sparrow densities were greatest (3.0 birds/ha) on a Loamy Fine Sand Ecological Site containing taller vegetation than vegetation for other ecological sites. Scientific literature commonly associates Brewer’s sparrows with sagebrush (Artemisia tridentata) presence, but on ecological sites at Browns Park Brewer’s densities are related more to vegetative structure rather than species composition. Results show there are links between passerine populations and ecological sites; a relationship which provides a meaningful foundation in developing long-term monitoring protocols and enhancing management decisions to favor sagebrush-obligate passerines

Songbird Relationships to Shrub-Steppe Ecological Site Characteristics

Rangeland managers are often faced with the complex challenge of managing sites for multiple uses and for the diverse interests of stakeholders. Standardized monitoring methods that can be used and understood by different agencies and stakeholders would aid management for long-term sustainability of rangelands. In the United States, federal land management agencies have recently based their assessments of rangeland health and integrity on state-and-transition models to consider management trajectories. Ecological sites provide a foundation for these efforts but have not been used to address wildlife habitat. Habitat preferences are documented for North American shrub-steppe songbirds but have yet to be related to ecological sites and site characteristics. We characterized ecological sites at Browns Park National Wildlife Refuge, Colorado, using established rangeland monitoring methods to test whether 1) songbird species density and diversity differ among adjacent shrub-steppe ecological sites and 2) quantifiable ecological site characteristics could be identified that account for significant variation in songbird density and diversity. Vegetation structure (represented as basal and canopy gaps, cover, height, and shrub density) differentiated the four ecological sites and was related to songbird density and diversity. Sage sparrows (Amphispiza belli) and vesper sparrows (Pooecetes gramineu) selected habitat based on horizontal characteristics of vegetation structure, such as basal and canopy gap and plant species cover. Brewer’s sparrow (Spizella breweri), lark sparrow (Chondestes grammacus), and songbird diversity were more strongly related to vegetation structure of the plant communities than to plant composition. Our results support use of ecological sites as management units to characterize songbird habitat given that songbird density and diversity were related to site vegetation characteristics. By incorporating basal and canopy gap, height, plant cover, and shrub density monitoring methods into ecological site descriptions, managers would be provided with additional tools to assist in differentiating songbird habitat.The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202