Patrick E. Clark

Applications and Research Using Remote Sensing for Rangeland Management

Rangelands are grasslands, shrublands, and savannas used by wildlife for habitat and livestock in order to produce food and fiber. Assessment and monitoring of rangelands are currently based on comparing the plant species present in relation to an expected successional end-state defined by the ecological site. In the future, assessment and monitoring may be based on indicators of ecosystem health, including sustainability of soil, sustainability of plant production, and presence of invasive weed species. USDA Agricultural Research Service (ARS) scientists are actively engaged in developing quantitative, repeatable, and low-cost methods to measure indicators of ecosystem health using remote sensing. Noxious weed infestations can be determined by careful selection of the spatial resolution, spectral bands, and timing of image acquisition. Rangeland productivity can be estimated with either Landsat or Advanced Very High Resolution Radiometer data using models of gross primary production based on radiation use efficiency. Lidar measurements are useful for canopy structure and soil roughness, indicating susceptibility to erosion. The value of remote sensing for rangeland management depends in part on combining the imagery with other spatial data within geographic information systems. Finally, ARS scientists are developing the knowledge on which future range-land assessment and monitoring tools will be developed.

Hydrologic Vulnerability of Sagebrush Steppe Following Pinyon and Juniper Encroachment

Abstract Woodland encroachment on United States rangelands has altered the structure and function of shrub steppe ecosystems. The potential community structure is one where trees dominate, shrub and herbaceous species decline, and rock cover and bare soil area increase and become more interconnected. Research from the Desert Southwest United States has demonstrated areas under tree canopies effectively store water and soil resources, whereas areas between canopies (intercanopy) generate significantly more runoff and erosion. We investigated these relationships and the impacts of tree encroachment on runoff and erosion processes at two woodland sites in the Intermountain West, USA. Rainfall simulation and concentrated flow methodologies were employed to measure infiltration, runoff, and erosion from intercanopy and canopy areas at small-plot (0.5 m2) and large-plot (13 m2) scales. Soil water repellency and vegetative and ground cover factors that influence runoff and erosion were quantified. Runoff and erosion from rainsplash, sheet flow, and concentrated flow processes were significantly greater from intercanopy than canopy areas across small- and large-plot scales, and site-specific erodibility differences were observed. Runoff and erosion were primarily dictated by the type and quantity of ground cover. Litter offered protection from rainsplash effects, provided rainfall storage, mitigated soil water repellency impacts on infiltration, and contributed to aggregate stability. Runoff and erosion increased exponentially (r2  =  0.75 and 0.64) where bare soil and rock cover exceeded 50%. Sediment yield was strongly correlated (r2  =  0.87) with runoff and increased linearly where runoff exceeded 20 mm·h−1. Measured runoff and erosion rates suggest tree canopies represent areas of hydrologic stability, whereas intercanopy areas are vulnerable to runoff and erosion. Results indicate the overall hydrologic vulnerability of sagebrush steppe following woodland encroachment depends on the potential influence of tree dominance on bare intercanopy expanse and connectivity and the potential erodibility of intercanopy areas.

Fire, Plant Invasions, and Erosion Events on Western Rangelands

Abstract Millions of hectares of rangeland in the western United States have been invaded by annual and woody plants that have increased the role of wildland fire. Altered fire regimes pose significant implications for runoff and erosion. In this paper we synthesize what is known about fire impacts on rangeland hydrology and erosion, and how that knowledge advances understanding of hydrologic risks associated with landscape scale plant community transitions and altered fire regimes. The increased role of wildland fire on western rangeland exposes landscapes to amplified runoff and erosion over short- and long-term windows of time and increases the risk of damage to soil and water resources, property, and human lives during extreme events. Amplified runoff and erosion postfire are a function of storm characteristics and fire-induced changes in site conditions (i.e., ground cover, soil water repellency, aggregate stability, and surface roughness) that define site susceptibility. We suggest that overall postfire hydrologic vulnerability be considered in a probabilistic framework that predicts hydrologic response for a range of potential storms and site susceptibilities and that identifies the hydrologic response magnitudes at which damage to values-at-risk are likely to occur. We identify key knowledge gaps that limit advancement of predictive technologies to address the increased role of wildland fire across rangeland landscapes. Our review of literature suggests quantifying interactions of varying rainfall intensity and key measures of site susceptibility, temporal variability in strength/influence of soil water repellency, and spatial scaling of postfire runoff and erosion remain paramount areas for future research to address hydrologic effects associated with the increased role of wildland fire on western rangelands.

An Advanced, Low-Cost, GPS-Based Animal Tracking System

Abstract An improved global positioning system (GPS)–based animal tracking system is needed to meet quickly evolving demands of ecological research, range livestock production, and natural resource management. Commercially available tracking systems lack the data storage capacity needed to frequently collect animal location data (e.g., 15-minute intervals or less) over long-term deployment periods (e.g., 1 year or more). Some commercial systems have remote data–download capabilities, reducing the need to recapture tagged animals for data retrieval, but these systems download data via satellite (Argos), global system for mobile communications (GSM) cellular telephone, or telemetry radio frequencies. Satellite systems are excessively expensive, and GSM cellular coverage is extremely limited within the United States. Radio-based systems use narrow-band very-high– or ultra-high frequencies requiring the user to obtain frequency allocations. None of these existing systems were designed to provide continual, real-time data access. The Clark GPS Animal Tracking System (Clark ATS) was developed to meet the evolving demands of animal ethologists, ecologists, natural resource managers, and livestock producers. The Clark ATS uses memory-card technology for expandable data storage from 16 megabytes to 8 gigabytes. Remote data downloading and program uploading is accomplished using spread-spectrum radio transceivers, which do not require narrow-band radio frequency allocations. These radios also transmit, at a user-defined time interval, a real-time, GPS-location beacon to any Clark ATS base station within range (about 24 km or 15 miles line of sight). Advances incorporated into the Clark ATS make it possible to evaluate animal behavior at very fine spatial- and temporal-resolution over long periods of time. The real-time monitoring provided by this system enables researchers to accurately examine animal distribution and activity responses to acute, short-term disturbances relative to longer-term behavioral patterns. The Clark ATS also provides a huge time- and cost-savings to researchers and natural resource managers attempting to relocate a tagged animal in the field for direct observation or other operations.

Hydrologic and Erosion Responses of Sagebrush Steppe Following Juniper Encroachment, Wildfire, and Tree Cutting

Abstract Extensive woodland expansion in the Great Basin has generated concern regarding ecological impacts of tree encroachment on sagebrush rangelands and strategies for restoring sagebrush steppe. This study used rainfall (0.5 m2 and 13 m2 scales) and concentrated flow simulations and measures of vegetation, ground cover, and soils to investigate hydrologic and erosion impacts of western juniper (Juniperus occidentalis Hook.) encroachment into sagebrush steppe and to evaluate short-term effects of burning and tree cutting on runoff and erosion responses. The overall effects of tree encroachment were a reduction in understory vegetation and formation of highly erodible, bare intercanopy between trees. Runoff and erosion from high-intensity rainfall (102 mm · h−1, 13 m2 plots) were generally low from unburned areas underneath tree canopies (13 mm and 48 g · m−2) and were higher from the unburned intercanopy (43 mm and 272 g · m−2). Intercanopy erosion increased linearly with runoff and exponentially where bare ground exceeded 60%. Erosion from simulated concentrated flow was 15- to 25-fold greater from the unburned intercanopy than unburned tree canopy areas. Severe burning amplified erosion from tree canopy plots by a factor of 20 but had a favorable effect on concentrated flow erosion from the intercanopy. Two years postfire, erosion remained 20-fold greater on burned than unburned tree plots, but concentrated flow erosion from the intercanopy (76% of study area) was reduced by herbaceous recruitment. The results indicate burning may amplify runoff and erosion immediately postfire. However, we infer burning that sustains residual understory cover and stimulates vegetation productivity may provide long-term reduction of soil loss relative to woodland persistence. Simply placing cut-downed trees into the unburned intercanopy had minimal immediate impact on infiltration and soil loss. Results suggest cut-tree treatments should focus on establishing tree debris contact with the soil surface if treatments are expected to reduce short-term soil loss during the postcut understory recruitment period.

Hydrothermal Assessment of Temporal Variability in Seedbed Microclimate

Abstract The microclimatic requirements for successful seedling establishment are much more restrictive than those required for adult plant survival. The purpose of the current study was to use hydrothermal germination models and a soil energy and water flux model to evaluate intra- and interannual variability in seedbed microclimate relative to potential germination response of six perennial grasses and cheatgrass. We used a 44-yr weather record to parameterize a seedbed microclimate model for estimation of hourly temperature and moisture at seeding depth for a sandy loam soil type at the Orchard Field Test Site in southwestern Ada County, Idaho. Hydrothermal germination response was measured in the laboratory for two seed lots of cheatgrass (Bromus tectorum L.), four seed lots of bluebunch wheatgrass (Pseudoroegneria spicata [Pursh] Löve), three seed lots of bottlebrush squirreltail (Elymus elymoides [Raf] Swezey), and one seed lot each of Sandberg bluegrass (Poa secunda J. Presl.), big squirreltail (Elymus multisetus [J.G. Smith] M.E. Jones), thickspike wheatgrass (Elymus lanceolatus [Scribn. And J.G. Smith] Gould) and Idaho fescue (Festuca idahoensis Elmer). Germination response models were developed to estimate potential germination rate for 13 subpopulations of each seed lot for every hour of the 44-yr simulation. Seedbed microclimate was assessed seasonally and for each day, month, and year, and germination rate-sum estimates integrated for a numerical index of relative site favorability for germination for each time period. The rate-sum favorability index showed a consistent pattern among seed lots for different years, and provides a relatively sensitive indicator of annual and seasonal variability in seedbed microclimate. This index could be used with field data to define minimum weather thresholds for successful establishment of alternative plant materials, in conjunction with weather forecast models for making restoration and fire-rehabilitation management decisions in the fall season, for evaluation of potential climate-change impacts on plant community trajectories, and in optimization schemes for selecting among alternative restoration/rehabilitation management scenarios.

Quantifying Vegetation Change by Point Sampling Landscape Photography Time Series

Abstract Quantitative assessment of vegetation change is often conducted by digitally analyzing time series of aerial or vertical photography. Change analysis conducted using repeated oblique or landscape photography, however, has been limited to qualitative assessments. The purpose of this study was to develop sampling and analysis techniques for using a time series of digitized landscape photography to quantify vegetation change on rangeland landscapes. Digital images were created from black-and-white landscape photographs acquired in 1917, 1962, and 2000 near Whiskey Mountain in the Reynolds Creek Experimental Watershed of southwestern Idaho. Images were spatially registered to each other using control points and a polynomial transformation algorithm. Thirty random pixels along each of 30 random image lines were selected as point samples (n = 900) from within each image. The landscape feature represented in each selected pixel was classified into 1 of 15 cover types. Cover-type classification accuracy for the 2000 image was estimated to be 92.2% based on ground-truth data collected in the field. Classification accuracy was increased to 98.9% by combining rare or poorly separable cover-type classes. Image cover of vegetation cover types was quantified for each photography acquisition date. Changes in image cover of each cover type and direction of cover-type conversions were determined for each intervening time period. Analysis of image cover using repeated landscape photography is constrained by limitations imposed by oblique view angles and variable image quality. Repeat landscape photography, however, can be used to quantitatively assess long-term dynamics of vegetation cover on rangeland landscapes with visually distinct vegetation types.

Estimating Sagebrush Biomass Using Terrestrial Laser Scanning

Abstract The presence of sagebrush (Artemisia tridentata) in rangelands has declined due to the invasion of annual grasses such as cheatgrass (Bromus tectorum) and the feedback between these flammable grasses and wildfire frequency. Monitoring the change and distribution of suitable habitat and fuel loads is an important aspect of sagebrush management, particularly under future climate conditions. Assessments of sagebrush biomass are used to monitor habitat for critical wildlife species, determine fire risk, and quantify carbon storage. Field techniques such as destructive and point-intercept sampling have been used to determine sagebrush biomass, but both of these techniques can be expensive and time consuming to implement. Light detection and ranging techniques, including airborne laser scanning and terrestrial laser scanning (TLS) have potential for rapidly assessing biomass in sagebrush steppe. This study used TLS to estimate biomass of 29 sagebrush plants in Reynolds Creek Experimental Watershed, Idaho. Biomass was estimated using TLS-derived volume, then compared with destructive samples to assess the estimation accuracy. This accuracy level was then contrasted with the estimates obtained using point-intercept sampling of the same plants. The TLS approach (R2 = 0.90) was slightly better for predicting total biomass than point-intercept sampling (R2 = 0.85). Prediction of green biomass, or production, was more accurate using TLS-derived volume (R2 = 0.86) than point-intercept sampling (R2 = 0.65). This study explores a promising new method to repeatedly monitor sagebrush biomass across extensive landscapes. Future work should focus on making this method independent of sensor type, scan distance, scan number, and study area.

Short-Term Impacts of Tree Removal on Runoff and Erosion From Pinyon- and Juniper-Dominated Sagebrush Hillslopes

abstract Tree removal is often applied to woodland-encroached rangelands to restore vegetation and improve hydrologic function, but knowledge is limited regarding effects of tree removal on hydrologic response. This study used artificial rainfall and overland flow experiments (9–13 m2) and measures of vegetation and ground cover to investigate short-term (1–2 yr) responses to tree removal at two woodland-encroached sites. Plots were located under trees (tree zone) and in the intercanopy (shrub-interspace zone, 75% of area). Before tree removal, vegetation and ground cover were degraded and intercanopy runoff and erosion rates were high. Cutting and placing trees into the intercanopy did not significantly affect vegetation, ground cover, runoff, or erosion 1 yr posttreatment. Whole-tree mastication as applied in this study did not redistribute tree mulch within the intercanopy, but the treatment did result in enhanced herbaceous cover and hydrologic function in the intercanopy. Fire removal of litter and herbaceous cover increased tree-zone runoff and erosion under high-intensity rainfall by 4- and 30-fold at one site but had minimal impact at the other site. Site response differences were attributed to variability in burn conditions and site-specific erodibility. Burning had minimal impact on shrub-interspace runoff and erosion from applied high-intensity rainfall. However, 1 yr postfire, erosion from concentrated overland flow experiments was 2- to 13-fold greater on burned than unburned tree-zone and shrub-interspace plots and erosion for burned tree zones was 3-fold greater for the more erodible site. Two yr postfire, overland flow erosion remained higher for burned versus unburned tree zones, but enhanced intercanopy herbaceous cover reduced erosion from shrub-interspace zones. The net impact of burning included an initial increase in erosion risk, particularly for tree zones, followed by enhanced herbaceous cover and improved hydrologic function within the intercanopy. The overall results suggest that erosion from late-succession woodlands is reduced primarily through recruitment of intercanopy herbaceous vegetation and ground cover.

Point Sampling to Stratify Biomass Variability in Sagebrush Steppe Vegetation

Abstract Cover and yield are two of the most commonly monitored plant attributes in rangeland vegetation surveys. These variables are usually highly correlated and many previous authors have suggested point-intercept estimates of plant cover could be used as a surrogate for more expensive and destructive methods of estimating plant biomass. When measurement variables are highly correlated, double sampling can be used to prestratify variability in the measurement that is more difficult or costly to obtain, thus improving sampling efficiency. The objective of this study was to examine the cost effectiveness of using point-intercept data to prestratify variability in subsequent clipped-biomass sampling on a sagebrush–bunchgrass rangeland site in southern Idaho. Point-intercept and biomass data were obtained for shrub, grass, and forb vegetation in 90 1-m2 plots. These data were used to develop a synthetic population of 10 000 simulated plots for conducting sensitivity analysis on alternative double-sampling scenarios. Monte Carlo simulation techniques were used to determine the effect of sampling design on cost and variability of biomass estimates as a function of point-intercept sample size (i), number of point-intercept sample strata (s), and number of biomass samples per stratum (m). Minimization of variability in biomass estimates were always obtained from double-sampling scenarios in which a single median biomass estimate was obtained for a given stratum in the point-intercept data. Double-sampling strategies in which half of the point-intercept plots were also measured for biomass yielded a cost savings of 39% with a reduction in biomass-sample precision of 18% ± 4 SD. The relative loss of precision in biomass estimates (62% ± 12 SD) became equal to the relative cost savings of double sampling for scenarios in which the ratio of point-intercept/biomass samples exceeded a value of five.