The efficacy of Moderate Resolution Imaging Spectroradiometer (MODIS)-derived vegetation productivity was tested in the grasslands of western North Dakota in terms of its ability to characterize fluctuations in aboveground green biomass and provide regional perspectives of interannual vegetation dynamics. To accomplish this task, we scaled plot-level observations of grassland biomass throughout the growing seasons of 2001 and 2002 using high-resolution satellite imagery and meteorological observations. Regionally scaled biomass measurements were compared with MODIS net photosynthesis (PSN_net) estimates at 3 times during the growing seasons of 2001 and 2002. The relationships between MODIS PSN_net estimates and scaled aboveground green biomass improved steadily during the progression of each growing season, and reached a maximum (r² = 0.77 and 0.57 in 2001 and 2002, respectively) near peak greenness. Aboveground green biomass was more tightly coupled in 2001 because of the relative abundance of green biomass compared with standing dead from the previous year. We characterized interannual variability in grassland vegetation through analysis of MODIS-derived net primary productivity (NPP) for the years 2001–2003. MODIS NPP estimates showed a significant decline (P ≤ 0.05) from 2001 to 2003, partly induced by a significant decline (P ≤ 0.05) in growing-season precipitation. The results indicate the reliability of productivity estimates for monitoring grassland biomass fluctuations is improved during years where plant growth conditions are more favorable. Additionally, MODIS data may be more useful for addressing administrative, rather than managerial, needs given the coarse resolution and regional perspective of the vegetation products.

Remote sensing data from the Advanced Very High Resolution Radiometer (AVHRR) have coarse spatial resolution (1 km² pixel size) and high temporal resolution, which can be used to estimate net primary production regionally. The normalized difference vegetation index (NDVI) is used to determine the fraction of absorbed photosynthetically active radiation, which is sensitive to differences in growth caused by a large year-to-year variation in precipitation. The 12-year average of net primary production was used to calculate stocking rates in animal-unit months per acre for the state of Wyoming. Stocking rates were also calculated for Wyoming from 1:500 000 scale soil and climate geospatial data layers based on stocking rates from the US Department of Agriculture Natural Resources Conservation Service Technician Guide to Range Sites and Range Condition. In a pixel-by-pixel comparison, there was a weak but significant correlation between the 2 methods based on the spatial distribution of precipitation. There were classes of vegetation type for which the AVHRR data predicted either much lower or much higher stocking rates. More work needs to be done to reduce geospatial data uncertainties for the determination of stocking rates from both NDVI and stocking rate tables. Remote sensing indicates the actual condition of vegetation, so this is an important step in the development of regional forecasting of range condition, trend, and projected stocking rates for decision support tools.

The degree of rangeland degradation in the United States is unknown due to the failure of traditional field-based monitoring to capture the range of variability of ecological indicators and disturbances, including climatic effects and land use practices, at regional to national spatial scales, and temporal scales of decades. Here, a protocol is presented for retrospective monitoring and assessment of rangeland degradation using historical time series of remote sensing data and catastrophe theory as an ecological framework to account for both gradual and rapid changes of state. This protocol 1) justifies the use of time-series satellite imagery in terms of the spatial and temporal scale of data collection; 2) briefly explains how to acquire, process, and transform the data into ecological indicators; 3) discusses the use of time-series analysis as the appropriate procedure for detecting significant change; and 4) explains what reference conditions are appropriate. Landsat data have been collected and archived since 1972, and include complete coverage of US rangelands. Characteristics of land degradation can be retrospectively measured for a nearly 33-year trend using surrogate remote sensing–based indicators that correlate with changes in life-form composition (time series of thematic maps), declines in vegetation productivity (vegetation indices), accelerated soil erosion (soil indices), declines in soil quality (piospheric analysis), and changes in landscape configuration (time series of thematic maps). Aspects of 2 retrospective studies are presented as examples of application of the protocol to considerations of the land use impacts from military training and testing and ranching activities on rangelands.

QuickBird satellite imagery was evaluated for differentiating among rangeland cover types on the Welder Wildlife Refuge in south Texas. The satellite imagery had a spatial resolution of 2.8 m and contained 11-bit data. Four subsets of the satellite image were extracted and used as study sites. Field spectral measurements made among the dominant vegetation types showed significant differences in visible and near-infrared reflectance. Unsupervised classification techniques were used to classify false color composite (green, red, and near-infrared bands) images of each study site. Accuracy assessments performed on the classification maps of the 4 sites had overall accuracies ranging from 79% to 89%. These results indicate that QuickBird imagery can be a useful tool for identifying rangeland cover types at a regional level.

With the development and commercial availability of submeter spatial resolution satellite imagery, geospatial tools can better accommodate the needs of range professionals than ever before. However, with these new tools comes a new set of challenges. Range managers and range scientists must now 1) better understand and take advantage of the geotechnical tools at their disposal, 2) collect field observations/measurements in ways that act synergistically with these tools, and 3) utilize high-accuracy global positioning system (GPS) receivers. To produce reliable rangeland models it is important to collect field data that correspond with what the satellite “sees.” Further, it is frequently necessary to use high-resolution imagery, which subsequently necessitates the use of high-accuracy GPS receivers to ensure field data are recorded in the correct pixel and properly coregistered. This paper describes the results of research and experimentation that have led to the development of techniques to improve geospatial rangeland applications. For optimal classification accuracy, field data collected for use in remote sensing applications should estimate/measure ground cover using general vegetation community types and must never exceed 100%. Further, the field sample sites used for classification must be located using a GPS receiver with accuracy ≤ 50% of the size of satellite imagery pixels (e.g., if Landsat imagery is used—with 28.5-m pixels—the GPS receiver must be able to achieve ± 14 m accuracy with 95% confidence). Finally, a series of best practices are suggested to help range managers and range scientists better understand and implement geospatial technologies.

Identifying the dynamics and extent of noxious weeds in a spatial and temporal context improves monitoring, planning, and management practices. Musk thistle (Carduus nutans L.), a noxious weed, is a good candidate for detection by remote sensing platforms because it may produce a unique spectral signature due to a large, purple-red flower head. Therefore, 3 remote sensing instruments—a ground hyperspectral spectrometer, a multispectral ground radiometer, and an airborne hyperspectral imaging spectrometer—were used to establish regression models between reflected data and the biophysical parameters (density, height, flower head density, and percent ground cover) of musk thistle. The coefficients of determination (R²) obtained from simple regression models for vegetation indices and musk thistle biophysical variables ranged from 0.46 to 0.77. Multiple regression models with up to 3 variables increased R² by an average of 0.07. This study indicated that normalized difference and simple ratio indices can be used for specific applications such as detection of musk thistle biophysical variables in rangelands. Once applied to the image, these results will produce a map of parameters that can be used to determine the size of infestation and the reduction in rangeland productivity.

Data describing long-term sediment yield rates on semiarid rangeland watersheds are relatively rare. To augment existing data and gain a better understanding of the controlling variables, sediment yields from 8 subwatersheds within the US Department of Agriculture–Agricultural Research Service Walnut Gulch Experimental Watershed in southeastern Arizona were computed from stock pond sediment accumulation measurements, water level records, and estimates of sediment transported in pond overflows. Sediment accumulation records ranging from 30 to 47 years were evaluated for subwatersheds ranging in size from 35.2 to 159.5 ha. Sediment yield ranged from 0.5 to 3.0 m³·ha⁻¹·y⁻¹, with a mean of 1.4 m³·ha⁻¹·y⁻¹ and a standard deviation of 1.0 m³·ha⁻¹·y⁻¹. As expected, runoff volume was a significant factor (P = 0.005) in explaining the variability in sediment yield, but regression analysis demonstrated other variables are important. For example, the ratio of watershed area to main channel length significantly described (P = 0.06) sediment yield, suggesting that more detailed measurements are needed to characterize channel networks to relate internal watershed sediment transport and deposition processes to sediment delivery at the outlets. To generalize sediment yield rates across rangeland regions, additional research is necessary to determine the relative influence of rainfall and runoff patterns, and watershed physiographic and geomorphic characteristics on sediment transport.

Sulfur cinquefoil (family Rosaceae) is an invasive, herbaceous perennial, native to Eurasia. It has wide ecological amplitude and has become established throughout North America in numerous habitat types. Sulfur cinquefoil reproduces only by seed (achenes); however, little is known about its regenerative strategy or reproductive biology. To improve understanding of the mechanisms of expansion for sulfur cinquefoil, we quantified seed production and measured seed dispersal at sites infested with sulfur cinquefoil in different habitats in northeast Oregon. Seed dispersal was measured by using sticky traps (30 × 100 cm, replaced every 2 weeks) radiating in 4 cardinal directions from individual source plants. Estimated seed production for 2 years (2001 and 2002) was nearly 4 times higher than previously reported (≈6 000 seeds per plant; range ≈ 2 620–15 150 seeds per plant). For most sites, seed production was similar in both years. However, site, year, and their interaction (site × year) had significant influence on flower and stem production. Seeds were dispersed from July through mid-October 2001, although almost 40% of the seeds were captured between mid-July and mid-August. Dispersal followed a classic decay function; approximately 83% of the seeds were captured within 60 cm of the source plants. Once sulfur cinquefoil reaches a site, it appears to spread and persist by releasing numerous seeds near the parent plants, thereby forming increasingly dense stands.

Prairie dogs (Cynomys spp.) have been labeled keystone species because of the role they play as disturbance creators and ecosystem engineers in the western grasslands of North America. Most studies have concentrated on the black-tailed species (C. ludovicianus); however, other species of prairie dogs may have different effects on their ecosystems. We measured plant cover and biomass, canopy height, and plant nitrogen concentration on and off 6 Gunnison's prairie dog (C. gunnisoni) towns and 6 paired areas off prairie dog towns in southern Colorado. Multivariate analysis of variance and analysis of variance showed no significant differences (P > 0.05) in vegetation cover or biomass on and off of Gunnison's prairie dog towns, contrary to what has been found for black-tailed prairie dog towns. No significant differences were found in canopy height (P > 0.05); however, this may be due to already short vegetation (5–7 cm). Only 1 of 4 focal plants showed a significant difference in nitrogen concentration. No significant differences were found in species diversity on and off prairie dog towns; however, because of drought, these results are inconclusive. This study found few vegetation differences on and off Gunnison's prairie dog towns. Furthermore, those differences were more subtle than those reported on black-tailed prairie dog towns. While the mechanisms for differences in vegetation on and off Gunnison's prairie dog towns may be similar to those on black-tailed prairie dog towns, the magnitude of these differences may be different.

Foraging niche overlap among Rocky Mountain elk (Cervus elaphus nelsoni), Rocky Mountain mule deer (Odocoileus hemionus hemionus), and cattle (Bos taurus) was studied for 2 years on 37 000 ha of nonforested foothill and mountain habitat in northwestern Wyoming. Microhistological analysis was used to quantify botanical composition of ungulate diets from monthly fecal collections. Feeding habitat use was determined through monthly surveys from fixed-wing aircraft to record nonsolitary animals in nonforested habitat. Kulcyznski's similarity index was used to calculate dietary and feeding habitat overlap among the 3 ungulates, and these 2 indices were multiplied together to estimate foraging niche overlap. In all seasons, elk and cattle consumed grass-dominated diets (mean = 61% and 81%, respectively), although elk diets were more diverse. Mule deer consumed more forbs and shrubs than either elk or cattle (P < 0.10). Foraging niche overlap was high (45%) between mule deer and elk in spring. Cattle in summer and fall had ≥60% foraging niche overlap with elk in spring, indicating that, in spring, elk foraged in many of the same places (largely sagebrush grassland) and ate diets similar in botanical composition to what cattle did during summer and fall (principally Festuca idahoensis, Pseudoroegneria spicata, and Achnatherum spp.). Foraging niche overlap also was high (41%–51%) between elk in winter and cattle in summer and fall. Therefore, if competitive or complementary relationships existed between elk and cattle, these interactions most likely occurred on sagebrush grasslands where cattle use in summer–fall was followed by elk use in winter–spring. We recommend that resource managers focus their forage utilization and range trend monitoring in foothill sagebrush grasslands.

Western juniper (Juniperus occidentalis spp. occidentalis Hook.) woodlands are rapidly replacing lower elevation (< 2 100 m) quaking aspen (Populus tremuloides Michx.) stands throughout the northern Great Basin. Aspen restoration is important because these communities provide critical habitat for many wildlife species and contain a high diversity of understory shrubs and herbaceous species. We studied two juniper removal treatments to restore aspen woodlands. Treatments included cutting one-third of the juniper trees followed by early fall burning (FALL) or early spring burning (SPRING). Selective cutting of juniper was performed to increase cured surface (0–2 m) fuel levels to carry fire through the woodlands. We tested treatment effectiveness at removing juniper from seedlings to mature trees, measured aspen sucker recruitment, and evaluated the response to treatment of shrub and herbaceous cover and diversity. In the FALL treatment, burning eliminated all remaining juniper trees and seedlings, stimulated a 6-fold increase in aspen suckering (10 000 ha⁻¹), but initially resulted in a significant reduction in herbaceous cover. Spring burning removed 80% of the mature juniper trees that remained after cutting. However, 50% of juniper juveniles survived the SPRING treatment, which will permit juniper to redominate these stands in less than 80 years. Aspen suckering in the SPRING increased only 2.5-fold to 5 300 stems ha⁻¹ by the third year after fire. In the SPRING, herbaceous cover increased 330% and the number of species observed doubled by the third year after fire. If the management objective is to eliminate western juniper with minimal cutting and stimulate greater aspen suckering, we recommend that woodlands be burned in the fall. If the objective is to maintain shrub and herbaceous cover and moderately increase aspen suckering, spring burning is recommended. With spring burning it appears follow-up management will be necessary to remove juniper that are missed in initial treatments.

Prescribed fire was used in two semiarid grasslands to reduce shrub cover, promote grass production, and reduce erosional loss that represents a potential non–point-source of sediment to degrade water quality. This study measured transported soil sediment, dynamics in soil surface microtopography, cover of the woody shrub, grass, and bare ground cover classes, and soil fertility measured by nitrogen-mineralization potentials for the respective cover classes over a 9-year period during which 2 fires occurred. In general, the effects of two drought periods were equal to or greater than the effects of fire on the measured parameters. Following the second fire at the grama grass-dominated site, the number of live junipers was significantly lowered (P < 0.001). Fire consumed grass and shrub cover, which created the potential for greater transport of sediment and loss in soil surface elevation. Soil fertility under shrubs was significantly higher than soil fertility under grasses in both grassland sites before and after the first fire; however, that highly significant pattern was not present after the second fire for about 2 years at both sites. This suggests that the reestablishment of a natural fire frequency would likely dampen the well-documented pattern of greater soil fertility under shrub islands relative to grass islands. Repeat use of prescribed fire may keep shrub cover in check and promote fundamental changes in soil processes within semiarid grasslands, but its value must be weighed against the increased potential for erosion following fire.