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The earth’s mountains continue to lose water. Glaciers are melting and mountain snow/rain balance tilts increasingly liquescent. Water is running off sooner—sometimes overfilling reservoirs, causing flooding, and setting the stage for late-season shortages. One adaptive strategy is to recover and enhance water-storage capacities of headwater riparian systems. Grazing, a common use of headwater lands, affects both soils and vegetation. To better understand how grazing might affect water storage and other ecosystem services of high elevation riparian wetlands, we measured soil-profile temperatures, soil organic matter (SOM), and phytomass at six sites in the upper Sweetwater River sub-basin of Wyoming, USA, where fence lines allowed us to contrast grazing management. We found grazed wetlands consistently had warmer soils than fenced wetlands. We found added evidence that SOM is important in both soil temperature control and water-storage potential of wetlands. We review evidence that warmer soil temperatures and drying cause loss of SOM with the implied concomitant C losses through erosion and emissions. We recommend land managers of temperate-climate headwater systems consider the need to end growing seasons with full stands of riparian vegetation to reduce soil warming and to build organic matter—particularly on lands where municipalities and other downstream water users are seeking long-term increases in water yields and less flooding.

Biodiversity decline is widely considered a critical global environmental threat. In the western United States, land surface disturbance associated with oil and gas development is considered a top ...

Rangeland ecosystems cover 3.6 billion hectares globally with 239 million hectares located in the United States. These ecosystems are critical for maintaining global ecosystem services. Monitoring vegetation in these ecosystems is required to assess rangeland health, to gauge habitat suitability for wildlife and domestic livestock, to combat invasive weeds, and to elucidate temporal environmental changes. Although rangeland ecosystems cover vast areas, traditional monitoring techniques are often time-consuming and cost-inefficient, subject to high observer bias, and often lack adequate spatial information. Image-based vegetation monitoring is faster, produces permanent records (i.e., images), may result in reduced observer bias, and inherently includes adequate spatial information. Spatially balanced sampling designs are beneficial in monitoring natural resources. A protocol is presented for implementing a spatially balanced sampling design known as balanced acceptance sampling (BAS), with imagery acquired from ground-level cameras and unmanned aerial systems (UAS). A route optimization algorithm is used in addition to solve the 'travelling salesperson problem' (TSP) to increase time and cost efficiency. While UAS images can be acquired 2-3x faster than handheld images, both types of images are similar to each other in terms of accuracy and precision. Lastly, the pros and cons of each method are discussed and examples of potential applications for these methods in other ecosystems are provided.

Penstemon haydenii Wats. (blowout penstemon, blowout beardtongue) is an early-succession plant species that is adapted to the dynamic habitats found in sand dunes. Following widespread habitat loss, the species was thought to be extinct from 1940 until it was rediscovered in 1968. It was listed as endangered in 1987 under the Endangered Species Act. At the time, it was only known from the Nebraska Sandhills, where its low numbers were ascribed to habitat loss. It was first discovered in Wyoming in 1996, in the Ferris Dunes of Carbon County. To develop a proxy for historic Wyoming habitat trends and a context for current conditions, we reconstructed the history of dunes where P. haydenii is presently located. Twelve georeferenced aerial photograph sets and digital imagery from 1946 to 2015 were analyzed to trace currently occupied dune areas back over the 70-year period. All currently occupied dunes were continuously present as areas of active sand over the 70-year timespan. Dune migration averaged 2.9 m/year. Dune extent declined 16.1% (2015 compared to the average). The continuity of active sand dune habitat and asynchronous trends in migration and in aerial extent between dunes and over time indicate a dynamic dune system maintained by wind erosion. These results provide critical context for population and habitat data of P. haydenii in Wyoming.

Headcuts are points of accelerated channel erosion that frequently have ecological consequences. A particularly large and dynamic headcut in southwest Wyoming has affected natural and anthropogenic resources for decades. To better understand and address this issue, we undertook a review of the headcut’s upstream retreat, followed by photogrammetric monitoring of the present condition for erosion monitoring. Aerial photography shows the Bitter Creek headcut retreated > 200 m upstream in 68 years (1948–2016) at ~ 1.4 m year−1. Following installation of a concrete slab structure in the mid-1970s, headcut retreat slowed to ~ 0.5 m year−1. Channel sinuosity downstream of the headcut is greater than upstream, which we attribute to the presence of the headcut, given that there are no major changes in valley geometry, geology, or soils through this reach. Both aerial and terrestrial-based image platforms were used to collect stereo imagery and create 3D photogrammetric models of the headcut in 2016. From these two models, we measured soil loss downstream of the headcut at ~ 126 m3 m−1 valley length. Since 1954, soil loss within the channel has been ~ 98 m3 year−1 or ~871 t ha−1 year−1since then. Models created from aerial- and terrestrial-based images differed in volumetric estimates by 2%, indicating that either method could be used for this type of monitoring. The ground-based imagery model showed more detail, especially on vertical and overhanging surfaces, while the aerial imagery model produced a more realistic orthomosaic and efficiently covered a larger area. Ground-based image acquisition took longer and was more costly per unit area, but is an efficient method for small project areas, or areas where aerial imagery cannot be safely or practically acquired. Historical imagery and photogrammetric modeling proved very useful in elucidating stream dynamics associated with this large, dynamic headcut.

Many rangeland streams and associated fisheries have suffered from livestock grazing as a cost of upland-forage utilization. Due to damage from intensive usage, restoration of damaged streams is now a common land-management objective. The Squaw Valley Ranch of Elko County, Nevada, US, in cooperation with the US Bureau of Land Management (BLM) and Barrick Gold Corp., is attempting to improve those portions of the Rock Creek watershed negatively affected by past ranch operations. The watershed includes both historical and occupied habitat for the threatened Lahonton cutthroat trout ( Oncorhynchus clarki henshawi [Richardson]). From 2003, and continuing to the present, hot-season livestock grazing on Squaw Valley Ranch private and permitted public-land riparian areas was greatly reduced. To assess the effectiveness of this conservation effort, we (1) evaluated BLM archived images of riparian photo points in the watershed, (2) tested for change over time using data from systematic, intermittent, aerial sampling that acquired 2-cm resolution images from low-altitude surveys conducted in 2003, 2004 and 2006, and (3) compared Landsat scenes of the area from before and after 2003. Willow ( Salix spp.) cover was chosen as the primary ecological indictor of riparian condition and we introduce willow canopy (m 2 ) per m of stream length in the image field-of-view, as a practical measure of willow status. Archived images from photo points show mostly low-condition riparian plant communities, often with little or no willow canopy evident before 2003, but with conspicuous improvement thereafter. This subjective perception is supported by objective analyses finding, (1) the relative increase in willow cover nearly tripled on one stream, more than doubled on three others, and increased on all but one (fire affected) and (2) a highly significant post-2003 increase in willows in the Landsat record. Thus, the post-2003 increase in willow cover documented in three complementary lines of evidence from ground, air, and space support the predicted ecological benefits of reduced hot-season riparian grazing and the utility of 2-cm imagery as a tool for assessing watershed-wide conservation benefits from a federal cost-share-eligible conservation practice. This appears to be the first use of willow measurements from an aerial survey as a particular indicator of riparian condition and trend and the first demonstration of change detection based on objective measurements from a watershed-scale riparian monitoring effort that used systematic sampling (versus subjective selection) and high sample density to address the large Type II error (false negative) risk common to conventional land-management survey efforts.

We used very large scale aerial (VLSA) photography to quantify spatial patterns in bare soil in the northeastern Colorado shortgrass steppe. Using three pairs of pastures stocked at moderate (0.6 animal unit months lAUM] · ha -1 ) versus very heavy (1.2 AUM · ha -1 ) rates, we detected greater bare soil under very heavy (mean = 22.5%) versus moderate stocking (mean = 13.5%; P = 0.053) and a lower coefficient of variation across pastures under very heavy (0.48) versus moderate stocking (0.75; P = 0.032). Bare soil exhibited significant positive spatial autocorrelation across distances of 60–120 m under moderate stocking (Moran's I = 0.14), while patchiness at this scale was eliminated under very heavy grazing ( I = -0.05). Across distances of 120–480 m, we observed no spatial autocorrelation with either stocking rate. Spatial autocorrelation was greatest at a separation distance of 2 m ( I = 0.48–0.58) but was unaffected by stocking rate at this scale. Thus, very heavy grazing did not increase spatial autocorrelation in bare soil across scales of 2–480 m. Means and variability in the distribution of bare soil were not influenced by ecological site. Bare soil increased primarily at the scale of individual plant clusters through both increases in the density of small (2–20 cm) bare patch intercepts and increases in the frequency of bare patch intercepts of 20–60 cm (rather than s 20 cm). Our approach demonstrates the utility of VLSA for analyzing interactions between grazing and other landscape features and highlights the importance of spatially explicit sampling across broad scales (pastures) while testing for potential shifts in patchiness of bare soil at the scale of plant interspaces.

Identifying environments where invasive plants are most invasive is key to understanding causes of invasion and developing effective management strategies. In mixed-grass prairie, invasive plants are often successful in relatively wet, nitrogen-rich areas, and areas protected from grazing. Dalmatian toadflax, a common invader of mixed-grass prairie, can also be favored by high water and nitrogen availability, but is thought to be relatively unpalatable to cattle, and therefore favored by grazing. We used spatially-adjusted model selection techniques to quantify relationships between toadflax cover (measured using very high-resolution aerial imagery), and relative snow deposition (estimated with a blowing snow model), slope, aspect, soil texture, and grazing intensity (estimated by proximity to water tanks). Toadflax was common throughout the 400 ha study site, occurring in 742 of 1,861 images. Toadflax cover was high on steeper slopes, particularly those with southern aspects. These two topographic variables were more effective in explaining toadflax distribution than modeled snow deposition, suggesting that factors other than snow deposition cause toadflax invasion on south-facing slopes. Toadflax cover was also high in areas further from water tanks, indicating that grazing may inhibit toadflax invasion. More broadly, this result suggests that grazing can reduce invasion of even relatively unpalatable species in ecosystems with long evolutionary histories of grazing.

Art to Science: Tools for Greater Objectivity in Resource Monitoring DOI:10.2458/azu_rangelands_v33i4_booth

High-resolution aerial surveys are a highly effective means for monitoring new and dispersed invasive-species infestations across extensive areas of wildland. Invasive species constitute a leading threat to native vegetation in wildland settings. Monitoring and controlling these species are essential actions to preserving nativeplant community integrity and historic wildland character. Infestations continue to increase. Monitoring with conventional ground or lower-resolution aerial data may be problematic as these tools are of questionable value for detecting small or dispersed weed populations. In July 2006, we conducted a dual-camera aerial survey acquiring 1-and 10-mm ground sample distance (GSD) imagery in the Medicine Lodge watershed in eastern Idaho. The survey included most of the 2003 Deep Fire Burn. Survey data were used to determine leafy spurge ( Euphorbia esula L. [Euphorbiaceae]) distribution on burned and unburned lands and to relate spurge distribution to ecosystem structure, associated vegetation, and control efforts. Leafy spurge was detected in 10% of 10-mm GSD samples versus 8% of 1-mm GSD samples. We conclude that 10-mm GSD is best for detecting leafy spurge because it optimizes the balance between resolution and field-of-view. Litter was about 4% greater where spurge was present than where it was not, and spurge occurrence was associated with significant decreases in cover of native grasses, forbs, and sagebrush ( Artemisia spp. L. [Asteraceae]). Leafy spurge proximity to water was higher than a random distribution would predict.

Greater Sage-Grouse (Centrocercus urophasianus) is a species of concern, and accurate population data are needed to monitor conservation management efforts. Conventional, ground-based lek counts are labor-intensive, expensive, and have several sources of potential error and bias, including the practical limits on number and distribution of leks counted. We tested aerial methods for photographing multiple leks during a single morning. We completed 14 aerial approaches to 6 leks in 2 different years using 2 different airplanes and altitudes. Grouse flushed from leks on 12 approaches when the airplane was within 200-300 m of the lek. In 2 instances, strutting grouse crouched and stayed on the lek. Our highest-resolution images increased our confidence in grouse identification but also decreased field-of-view coverage to the detriment of count accuracy. The methods we tested do not allow sage-grouse to be accurately counted, but the results provide information about sage-grouse responses to low-altitude airplane approaches and about useful image resolutions and fields of view.

Shadow often interferes with accurate image analysis. To mitigate shadow effects in near-earth imagery (2 m above ground level), we created high dynamic range (HDR) nadir images and used them to measure grassland ground cover. HDR composites were created by merging three differentially exposed images spanning a wide exposure range and resulted in lightened shadows. HDR images showed more detail; reduced the numbers of pure black, pure white, and pixels visually indistinguishable from black and white; reapportioned skewed luma values towards a normal distribution; and increased the Euclidean distance between litter and bare ground RGB values--allowing increased feature separation; all of which facilitated an increase in real feature classification through manual image analysis. Drawbacks to the method included decreased image sharpness due to minor misalignment of images or moving vegetation, time required to create HDR images, and difficulty with acquiring primary images from a moving platform. We conclude that HDR imagery can provide more accurate measurements of bare soil cover for ecosystem monitoring and assessment.

Energy-extraction results in significant disturbance to rangelands in Wyoming and other western US states. Although reclamation is required by law, US General Accounting Office reports from 1999 and 2005 are clear that affected government agencies have--over much of the past decade--had difficulty accomplishing mandated environmental monitoring of extraction-related disturbance. We evaluated two pipeline rights of way (ROW) using nested images (1- or 2- with 13- or 20-mm ground sample distance (GSD)) acquired during Very-Large Scale Aerial (VLSA) surveys. Aerial monitoring allowed for the collection of large numbers of geocoded samples, and for subsequent cover measurements using methods with demonstrated accuracy equal to that of conventional ground-based methods. Both pipelines had vegetative-cover deficiencies relative to their Plan of Development (POD) requirements. Using bare ground and ground-cover measurements from the higher-resolution imagery, we present a spatial representation of each pipeline ROW that allows quick identification of sections of the ROW that may need further reclamation action to meet POD standards. We also present aerial monitoring costs. We recommend VLSA pipeline surveys as a means for facilitating required environmental monitoring and for addressing the monitoring backlog that has developed with increased energy-extraction activity.

High-resolution, image-based methods can increase the speed and accuracy of ecological monitoring while reducing monitoring costs. We evaluated the efficacy of systematic aerial and ground sampling protocols to detect stocking-rate differences across 130 ha of shortgrass prairie. Manual (SamplePoint) and automated (spectral) image-analysis methods were compared for both aerial and ground data. Vegetative cover changes due to grazing were detectable from 1-mm ground sample distance (GSD, a measure of resolution) digital aerial photography with as few as 30 samples yielding enough data to predict bare ground within ± 5%. We found poor agreement between automated and manual image-analysis methods, but good agreement between manual analyses of imagery from the air (100 m above ground level [AGL]) and from the ground (2 m AGL). We conclude that cover measurements made using SamplePoint from 1-mm GSD images (from 2 or 100 m AGL) can detect ecologically important changes in key indicators such as bare ground. The costs of ground and aerial methods differ markedly, and we suggest that aerial imagery is most cost effective for areas larger than 200 ha.

Wyoming's Green Mountain Common Allotment is public land providing livestock forage, wildlife habitat, and unfenced solitude, amid other ecological services. It is also the center of ongoing debate over USDI Bureau of Land Management's (BLM) adjudication of land uses. Monitoring resource use is a BLM responsibility, but conventional monitoring is inadequate for the vast areas encompassed in this and other public-land units. New monitoring methods are needed that will reduce monitoring costs. An understanding of data-set relationships among old and new methods is also needed. This study compared two conventional methods with two remote sensing methods using images captured from two meters and 100 meters above ground level from a camera stand (a ground, image-based method) and a light airplane (an aerial, image-based method). Image analysis used SamplePoint or VegMeasure software. Aerial methods allowed for increased sampling intensity at low cost relative to the time and travel required by ground methods. Costs to acquire the aerial imagery and measure ground cover on 162 aerial samples representing 9000 ha were less than $3000. The four highest correlations among data sets for bare ground--the ground-cover characteristic yielding the highest correlations (r)--ranged from 0.76 to 0.85 and included ground with ground, ground with aerial, and aerial with aerial data-set associations. We conclude that our aerial surveys are a cost-effective monitoring method, that ground with aerial data-set correlations can be equal to, or greater than those among ground-based data sets, and that bare ground should continue to be investigated and tested for use as a key indicator of rangeland health.

Satellite and high-altitude aerial remote sensing have been used to measure dense infestations of invasive weeds over very large areas but have limited resolution and cannot be used to detect sparsely distributed weeds. Ground-based methods have provided detailed measurements of invasive weeds but can measure only limited areas. Here we test a novel approach that uses a lightweight airplane, flying at 72 km ? h 21 and 100-m altitude, to rapidly collect high-resolution images over relatively large areas. We obtained 1 987 images, each representing 48.5 m 2 of mixed-grass prairie with 2-mm resolution (ground sample distance). From these images we were able to reliably measure small patches and even individual plants of the invasive forb Dalmatian toadflax (Linaria dalmatica [L.] P. Mill.). Ground-based measurements of aboveground toadflax biomass were highly correlated (R 2 . 0.93) with point-intercept and visual-estimate cover measurements from aerial images. The time required to analyze images ranged from 4 to 45 seconds for presence/absence data and from 1 to 6 minutes for cover data. Toadflax was present in 795 of 1 987 images but exceeded 1% cover in only 99 images. Given the observed variation among images in toadflax cover, at least 400 images were needed to precisely estimate the mean toadflax cover of 0.2%. These results suggest that such high-resolution aerial imagery could be used to obtain detailed measurements of many invasive weed populations. It may be most useful for identifying incipient weed infestations and expanding the scale at which population-level attributes of weed populations can be effectively measured.

Riparian monitoring is a key aspect of sustainable resource management and is mandated by US federal law for federal land management agencies. However, it is an endeavor hampered by rising manpower costs and time-consuming travel and methods. These limitations tend to reduce sampling intensity per reach of stream and limit monitoring to the larger waterways of management units—limitations that reduce the accuracy of inferences derived from resulting data with consequential reductions in the effectiveness of landscape-level resource management. We tested the utility of low-altitude, high-resolution, intermittent aerial digital imagery for relatively inexpensive, high-intensity sampling in a watershed inhabited by the Lahonton Cutthroat trout, a species listed as threatened under provisions of the US Endangered Species Act. Measurements gleaned from the aerial imagery included late-summer open water width, number and location of late-summer dry channels, widths of riparian areas and willow coverage. All measurements were georeferenced to allow spatial data display. Riparian proper functioning condition (PFC) was assessed from the imagery by a USDI, Bureau of Land Management team. These assessments were compared to similar on-the-ground assessments made during the preceding year. PFC assessments from aerial photography were made using an average 4 staff hours per stream compared to an estimated 36 staff hours per stream for ground PFC assessments. The two assessment methods yielded roughly comparable results. We conclude that riparian-condition assessments from 2-cm GSD digital aerial imagery allowed increased sample intensity (and thus increased inference accuracy) and that it did so in our study at a cost less than half that of conventional ground-based methods. We recommend the acquisition and analysis of 2-cm GSD digital aerial imagery be further trialed for its utility and cost efficiency in ecological monitoring of riparian systems.

Ecological assessment of ground cover by conventional on‐the‐ground point sampling is labor intensive, expensive, and biased by access. Historically, motion blur has prevented high‐resolution aerial photography from being used for ground cover measurements. To reduce motion blur we used a fixed‐wing, 225‐kg (empty weight) airplane flown at 72 km/hr ground speed 100 m above ground level with both a modified Hulcher 70 mm camera (500 mm lens, Kodak Aerocolor HS SO‐846 film, 1/4,000‐second shutter speed), and a Canon 11. 1 ‐megapixel, automatic, digital single lens reflex, color camera (420 mm focal‐length lens). The resulting very‐large scale aerial (VLSA) photography had resolutions of 5.0 and 2.1 mm GSD (Ground Sample Distance) for the scanned film and digital‐camera images, respectively. Motion blur was minimal. The cost for obtaining 450 VLSA photographs over a 70,800‐ha watershed was $0.07 ha. We found our methods well adapted for extensive aerial surveys to monitor the ecological condition of...

Managers need measurements and resource managers need the length/width of a variety of items including that of animals, logs, streams, plant canopies, man-made objects, riparian habitat, vegetation patches and other things important in resource monitoring and land inspection. These types of measurements can now be easily and accurately obtained from very large scale aerial (VLSA) imagery having spatial resolutions as fine as 1 millimeter per pixel by using the three new software programs described here. VLSA images have small fields of view and are used for intermittent sampling across extensive landscapes. Pixel-coverage among images is influenced by small changes in airplane altitude above ground level (AGL) and orientation relative to the ground, as well as by changes in topography. These factors affect the object-to-camera distance used for image-resolution calculations. 'ImageMeasurement' offers a user-friendly interface for accounting for pixel-coverage variation among images by utilizing a database. 'LaserLOG' records and displays airplane altitude AGL measured from a high frequency laser rangefinder, and displays the vertical velocity. 'Merge' sorts through large amounts of data generated by LaserLOG and matches precise airplane altitudes with camera trigger times for input to the ImageMeasurement database. We discuss application of these tools, including error estimates. We found measurements from aerial images (collection resolution: 5-26 mm/pixel as projected on the ground) using ImageMeasurement, LaserLOG, and Merge, were accurate to centimeters with an error less than 10%. We recommend these software packages as a means for expanding the utility of aerial image data.

New methods of image acquisition and analysis are advancing rangeland assessment techniques. Most image-analysis programs require users to adjust detection thresholds for color or object classification, a subjective process we postulated would be influenced by human error and variation. We developed a ground-cover–measurement calibration procedure, the digital grid overlay (DGO), which is similar to image point sampling (dot grid) advanced by earlier researchers. We asked 21 rangeland professionals to measure ground cover using 2 subjective visual-estimate methods (threshold adjustment process, or TAP, and external [to the software] visual estimate, or EVE) and the DGO on 5 different nadir-view images of rangeland. We also compared cover measurements made by DGO-calibrated software in automated batch processing against DGO manual-only measurements. We found an unacceptable range of variation among rangeland professionals using TAP. The DGO and EVE values were more closely aligned. We discovered an age-related bias in bare-ground measurements: all users over 50 years of age classified more bare ground than did all users under 50 years of age when using TAP. One explanation for this bias is age-related yellowing of the eye lens. Manual DGO measurements required up to 15 minutes per image compared to about 1 second per image for automated computer analysis after software calibration. The greatest bare-ground difference between the DGO-calibrated software and manual DGO measurements for the data sets analyzed was 5.6% and the correlations imply that reasonably accurate automated measurements can be used for bare-ground measurements from digital-image data sets. The exception is where the software cannot adequately separate litter and bare ground. The digital methods we tested need improvement. However, external calibration (DGO or EVE) of current-generation image-analysis algorithms bring economical, statistically adequate monitoring of extensive land areas within the realm of practical application.

Ground cover is a key indicator of rangeland health but conventional methods for measuring ground cover are labor intensive. Analysis of digital images has the potential to reduce ground-cover-measurement labor requirements. We compared cover measurements by image analyses of digital images (sensor resolution = 0.97 mm/pixel ground sample distance) with measurements derived from a laser point frame, and from two transect methods. We found there was low agreement in plot-to-plot comparisons but results were usually not different when averaged over a large number of plots or transects. We conclude that image analysis of large numbers of samples (images) produce mean values not different from conventional field methods, and, that image analysis is a superior choice for detecting relative change, since it facilitates greater data collection, reduces human bias by limiting human judgments, and provides a permanent record in images that can be retained for future scrutiny.

Digital photography and subsequent image analysis for ground-cover measurements can increase sampling rate and measurement speed and probably can increase measurement accuracy. Reduced monitoring time (labor cost) can increase monitoring precision by allowing for increased sample numbers. Multiple platforms have been developed for close-to-earth remote sensing. Here we outline a new, 5.8-kg aluminum camera stand for acquiring stereo imagery from 2 m above ground level. The stand is easily transported to, from, and within study sites owing to its low weight, excellent balance, and break-down multipiece construction.

Increasing human population and intensive land use combined with a warming climate and chronically diminished snowpacks are putting more strain on water resources in the western United States. Properly functioning riparian systems slow runoff and store water, thus regulating extreme flows; however, riparian areas across the west are in a degraded condition with a majority of riparian systems not in proper functioning condition, and with widespread catastrophic erosion of water-storing peat and organic soils. Headcuts are the leading edge of catastrophic channel erosion. We used aerial imagery (1.4-3.3-cm pixel) to locate 163 headcuts in riparian areas in the Sweetwater subbasin of central Wyoming. We found 1-m-the generally available standard resolution for land management-and 30-cm pixel imagery to be inadequate for headcut identification. We also used Structure-from-Motion models built from ground-acquired imagery to model 18 headcuts from which we measured soil loss of 425-720 m3. Normalized by channel length, this represents a loss of 1.1-1.8 m3 m(-1) channel. Monitoring headcuts, either from ground or aerial imagery, provides an objective indicator of sustainable riparian land management and identifies priority disturbance-mitigation areas. Image-based headcut monitoring must use data on the order of 3.3 cm ground sample distance, or greater resolution, to effectively capture the information needed for accurate assessments of riparian conditions.

Changes in metabolism that accompany cold acclimation and deacclimation, such as increasing levels of raffinose family oligosacharides (RFO) during cold acclimation demonstrated in several woody species, are of interest in a search for genetic control of environmental adaptation by cold-hardy woody plants. This study examined the rela- tionship of temperature to endodormancy and cold hardiness in trembling aspen (Populus tremuloides Michx.) buds col- lected at 1560, 2250, and 2900 m elevation near Fort Collins, Colo. Buds from all sites tolerated at least -85°C in December, and buds from 2900 m, the highest elevation, hardened most quickly in fall and retained their hardiness the longest in late winter and early spring. Exposure to liquid nitrogen caused bud break in normally endodormant (15 No- vember collection date) buds. RFO levels were highly correlated to low temperature during acclimation and to lowest survival temperatures. Endogenous raffinose and stachyose increased as temperatures dropped in early winter and di- minished as temperatures rose in spring. Arrhenius plots showed that raffinose accumulation was strongly low- temperature dependent during acclimation. Its loss, while also temperature dependant in spring, was not as pronounced as during fall acclimation. Buds from all three sites survived cryopreservation at -196°C when first prefrozen at 5°C/h and stored >4 h at -20°C or colder. Differential scanning calorimetry data suggest that an aqueous component froze separately from tissues that underwent a glass transition in buds that survived cryopreservation. This study documents a complete dormant season hardiness profile of aspen linking hardiness with changes in endogenous soluble sugars. Resume : Les changements metaboliques associes a l'acclimatation au froid et a la desacclimatation, tels que l'augmentation des teneurs en oligosaccharides de la famille des raffinoses (OFR) rapportee pour plusieurs especes li- gneuses pendant l'acclimatation au froid, presentent un interet pour la recherche du controle genetique de l'adaptation des plantes ligneuses tolerantes au froid. Cette etude a examine la relation entre la temperature, la dormance et la tole- rance au froid de bourgeons de peuplier faux-tremble (Populus tremuloides Michx.) echantillonnes a 1560, 2250 et 2900 m d'altitude pres de Fort Collins, au Colorado. Les bourgeons de tous les sites ont tolere au moins -85°C en de- cembre et ceux de l'altitude la plus elevee, 2900 m, se sont endurcis plus vite en automne et ont conserve leur endur- cissement plus longtemps a la fin de l'hiver et au debut du printemps. Une immersion des bourgeons dormants dans l'azote liquide a provoque leur debourrement (echantillonnage du 15 novembre). Les teneurs en OFR etaient hautement correlees avec les basses temperatures durant l'acclimatation ainsi qu'avec les temperatures minimales auxquelles survi - vaient les bourgeons. Les teneurs en raffinose et en stachyose endogenes ont augmente avec la diminution des tempera- tures au debut de l'hiver et ont diminue avec l'augmentation des temperatures au printemps. Des graphiques d'Arrhenius montrent que l'accumulation de raffinose est etroitement reliee aux basses temperatures durant l'acclimatation. La diminution du raffinose au printemps est aussi reliee a la temperature mais moins que lors de l'acclimatation a l'automne. Les bourgeons des trois sites ont survecu a la cryopreservation a -196°C lorsqu'ils etaient d'abord refroidis a 5°C/h et entreposes pour plus d e4haa u moins-20°C. Les donnees d'analyse calorimetrique dif- ferentielle suggerent que dans les bourgeons qui survivaient a la cryopreservation une constituante aqueuse gelait sepa - rement des tissus qui subissaient une vitrification. Cette etude presente un profil complet de l'evolution de l'endurcissement durant la periode de dormance du peuplier faux-tremble et met en evidence la relation entre l'endurcissement et les changements dans la teneur en sucres solubles endogenes. (Traduit par la Redaction) Cox and Stushnoff 737

Measuring percent occurrence of objects from digital images can save time and expense relative to conventional field measurements. However, the accuracy of image analysis had, until now, not reached the level of the best conventional field measurements. Additionally, most image-analysis software programs require advanced user training to successfully analyze images. Here we present a new software program, 'SamplePoint,' that provides the user a single-pixel sample point and the ability to view and identify the pixel context. We found SamplePoint to allow accuracy comparable with the most accurate field-methods for ground-cover measurements. Expert use of the program requires minimal training and its ease of use allows rapid measurements from image data. We recommend SamplePoint for calibrating the threshold-detection level of image-analysis software or for making direct measurements of percent occurrence from digital images.

Ground cover is a key indicator of rangeland condition and influences rangeland management decisions, yet there have been few advances in ground-cover measurement methods. The advent of digital photography and automated image processing promise a revolution in the way ground cover is measured. To assess the potential for automation we compared conventional and automated methods for measuring ground cover against known artificial populations. The known populations were created from 20 nadir images of a Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle Young) vegetation type acquired with a 5-megapixel Olympus E20 digital single lens reflex camera mounted on an aluminum camera frame at 2 m above ground level. The images were converted to color, 2-dimensional images that no longer represented real-world conditions but had known cover values and conserved a simplified form of the pattern and spatial context of the plant community. These images were then printed at 1:1 scale to a 1 X 1-m poster. Posters were evaluated for color cover under laboratory conditions using the conventional techniques of steel-point frame, laser-point frame, line-point intercept, ocular estimation, and line intercept. Photographs of the posters were measured for color cover using standard and custom-created algorithms within the VegMeasure image analysis framework, and using the Digital Grid Overlay method. Results indicate that conventional techniques had significantly greater correlation (92% agreement of measured to known) than measurements from the algorithms used in the VegMeasure analysis (70%). The critical factor influencing accuracy of point-sampling methods was the area of the contact point for the given method. These findings provide an important measure of relative accuracy among methods for land managers and for researchers seeking to improve rangeland monitoring methods.

Phlorizin is known for its role in reducing glucotoxicity and has a long history of use in diabetes research. In addition, its contribution to the pool of total phenolics adds to the overall health benefits attributed to fruit. Phlorizin is limited to Rosaceae family plants, of which apple comprises its current commercial source; however, limited information exists regarding its biodiversity among apple taxa. A subset of 22 taxa from a core collection of apple accessions representative of the global genetic diversity of apple was used to investigate the biodiversity of phlorizin present in apple shoots and in fruit relative to total phenolic content and free radical scavenging capacity. Fruit and shoots were harvested from the USDA Plant Genetic Resources Unit in Geneva, N.Y. Validation and quantification of phlorizin was conducted using a rigorous high-pressure liquid chromatography (HPLC) procedure. Total phenolics in fruit, assayed using a Folin-Ciocalteu method and expressed as gallic acid equivalents, ranged from 227 to 7181 mg·L-1 and were strongly related to 2,2' azinobis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) antioxidant capacity for the core collection (r= 0.778). On a molar basis, phlorizin had lower antioxidant capacity than other major phenolic compounds present in apple fruit, but was more effective than ascorbic acid. Phlorizin yield in dormant apple shoots, expressed as percent weight, ranged from 0.9% to 5.5%. A rapid, 96 well micro-plate spectrophotometric assay was also developed to aid in the screening of multiple samples for selection of high phlorizin yielding apple taxa. Spectrophotometry overestimated phlorizin content as expected, but the calibration curve between HPLC and spectrophotometry was acceptable, r2 = 0.88.