Search

Spatial association between pine recruitment and shrubs is widely observed in dry environments and often associated with physical facilitation provided by the shrub, alleviating seedling drought stress. However, shrubs may also facilitate recruitment by sheltering seeds from granivores. In this study we investigated the influence of shrub-related microsites on post-dispersal pine seed survival in dry Mediterranean shrubland. We present a novel approach investigating the survival of single seeds in the context of long-distance wind dispersal. In four dry shrubland sites of central Israel, we placed seeds of Pinus halepensis in different microsites associated with Sarcopoterium spinosum shrubs: under canopy, at two margins and in between shrubs. We monitored the seed persistence monthly, replacing seeds removed by granivores. We also compared seed survival in burned vs. unburned areas. Logistic regression showed that seeds placed under shrubs had significantly higher survival rates than elsewhere. In unburned sites survival was higher than in burned sites and remained higher under shrub canopies. We show that these effects were substantial by considering the length of the season through which seeds need to persist. We conclude that shrubs constitute an important facilitator for Pinus halepensis colonization in dry shrubland through their positive effect on seed survival.

We examined variations in the relative importance of facilitation vs. competition, in light of the Stress-Gradient Hypothesis (SGH) by assessing plant interactions along an aridity gradient over biogeographic scales. We surveyed the relationship between a shrub species (Artemisia tridentata) and pine seedlings (Pinus monophylla) across the Great Basin and the Mojave Desert, USA, encompassing the entire range of P. monophylla. Using 69 sites we evaluated the spatial association between P. monophylla seedlings and A. tridentata shrubs, quantified with an electivity index, and implemented multiple regression analysis on the effects of macro- and micro-environmental factors: precipitation, temperature, monsoonality index, topography, substrate and litter cover. We identified annual precipitation as a main factor, which was negatively related to shrub-seedling association. Additionally, shrub-seedling association was stronger in the hot- than in the cold-desert, and was negatively related to litter cover. Effects of monsoonality, summer temperature, and bedrock type were not significant. We also considered nonlinear functional forms of a precipitation–electivity relationship, but the negative linear model proved most predictive. Our observations match SGH predictions. Studying the role of interspecific interactions in shaping species range shifts may lead to improved predictions of distribution ranges and changes in dryland vegetation under global change scenarios.

Although water is a contentious resource in terms of human use and consumption, particularly in the southwestern United States (U.S.), its presence is not always considered valuable or welcome. Where water accumulates on the flat, hard surfaces of desert playas used for the military mission, ephemeral conflict with nature occurs; conflict present only so long as standing water persists into scheduled use for training and testing. Flood occurrences on playas where runways and flightlines are established may incur added financial burden due to unanticipated scheduling changes in training and testing, or damage to infrastructure. The ability to better estimate and predict flooding events including duration and frequency of inundation, which could affect use of playas with infrastructure, may present range managers with a means to avert potential conflicts. For this reason examining the current model that incorporates watershed parameters and Doppler-radar precipitation measurements to estimate runoff onto Rogers (Dry) Lake at Edwards Air Force Base (EAFB), U.S.A. was done. Satellite imagery and digital elevation model data are spatially explicit (associated with a geographic location) and present that advantage both for planning and to provide comparison of model estimates. The degree to which either or both approaches reflect ground condition following storm events was quantified. Pre- and post-standing water extent for the two significant rainfall-runoff events was mapped from Landsat satellite imagery and standing water volume on the playa was then calculated using a high spatial resolution LiDAR–derived digital elevation model (DEM). These results were compared to the runoff volume estimates made from a model that extrapolated precipitation from Doppler-radar and meteorological stations within the Rogers Lake watershed. The results showed both over- and under-estimated playa inundations when compared.

Human Remains Detection (HRD) dogs can be a useful tool to locate buried human remains because they rely on olfactory rather than visual cues. Trained specifically to locate deceased humans, it is widely believed that HRD dogs can differentiate animal remains from human remains. This study analyzed the volatile organic compounds (VOCs) present in the headspace above partially decomposed animal tissue samples and directly compared them with results published from human tissues using established solid-phase microextraction (SPME) and gas chromatography/mass spectrometry (GC/MS) methods. Volatile organic compounds present in the headspace of four different animal tissue samples (bone, muscle, fat and skin) from each of cow, pig and chicken were identified and compared to published results from human samples. Although there were compounds common to both animal and human remains, the VOC signatures of each of the animal remains differed from those of humans. Of particular interest was the difference between pigs and humans, because in some countries HRD dogs are trained on pig remains rather than human remains. Pig VOC signatures were not found to be a subset of human; in addition to sharing only seven of thirty human-specific compounds, an additional nine unique VOCs were recorded from pig samples which were not present in human samples. The VOC signatures from chicken and human samples were most similar sharing the most compounds of the animals studied. Identifying VOCs that are unique to humans may be useful to develop human-specific training aids for HRD canines, and may eventually lead to an instrument that can detect clandestine human burial sites.

Avulsed teeth can be difficult if not impossible to recover in the outdoor environment, yet are important for victim identification. This study assessed dog teams as a resource to locate human teeth in a field setting and related performance in training with field capability. Standardized, objective training data were recorded and analyzed followed by double-blind capability trials. In the double-blind trials, 10 teeth were placed in each of six (10 m(2)) plots. Search time per plot ranged from 27 to 50 min, and the proportion of teeth found by the teams varied between 0.20 and 0.79. Using 0.45 m as a distance criterion for a "find," the proportion of false positives ranged between 0.07 and 0.75. Results show that dog teams are capable of recovering individual human teeth in the field setting with high precision although capability varies. Training records support a team's expected field performance. Additional studies are needed.

The use of dogs (Canis lupus familiaris) trained to locate wildlife under natural conditions may increase the risk of attracting potential predators or alter behavior of target species. These potentially negative effects become even more problematic when dealing with threatened or endangered species, such as the Mojave Desert tortoise (Gopherus agassizii). We addressed three concerns regarding use of dogs trained to locate desert tortoises in the wild. First, we looked at the potential for dogs to attract native and non-native predators to sites at a greater rate than with human visitation alone by comparing presence of predator sign before and after visitation by dogs and by humans. We found no significant difference in predator sign based upon type of surveyor. Second, we looked at the difference in risk of predation to desert tortoises that were located in the wild by humans versus humans with wildlife-detector dogs. Over a 5-week period, during which tortoises were extensively monitored and a subsequent period of 1 year during which tortoises were monitored monthly, there was no predation on, nor sign of predator-inflicted trauma to tortoises initially encountered either by humans or wildlife-detector dogs. Third, we looked at movement patterns of tortoises after encounter by either humans or wildlife-detector dogs. Movement of desert tortoises was not significantly different after being found by a human versus being found by a wildlife-detector dog. Based upon these initial results we conclude that use of trained wildlife-detector dogs to survey for desert tortoises in the wild does not appear to increase attraction of predators, increase risk of predation, or alter movement patterns of desert tortoises more than surveys conducted by humans alone.

The current ecological state of the Lake Tahoe basin has been shaped by significant landscape-altering human activity and management practices since the mid-1850s; first through widespread timber harvesting from the 1850s to 1920s followed by urban development from the 1950s to the present. Consequences of landscape change, both from development and forest management practices including fire suppression, have prompted rising levels of concern for the ecological integrity of the region. The impacts from these activities include decreased water quality, degraded biotic communities, and increased fire hazard. To establish an understanding of the Lake Tahoe basin’s landscape change in the context of forest management and development we mapped, quantified, and described the spatial and temporal distribution and variability of historical changes in land use and land cover in the southern Lake Tahoe basin (279 km 2 ) from 1940 to 2002. Our assessment relied on post-classification change detection of multi-temporal land-use/cover and impervious-surface-area data that were derived through manual interpretation, image processing, and GIS data integration for four dates of imagery: 1940, 1969, 1987, and 2002. The most significant land conversion during the 62year study period was an increase in developed lands with a corresponding decrease in forests, wetlands, and shrublands. Forest stand densities increased throughout the 62-year study period, and modern thinning efforts resulted in localized stand density decreases in the latter part of the study period. Additionally forests were gained from succession, and towards the end of the study period extensive tree mortality occurred. The highest rates of change occurred between 1940 and 1969, corresponding with dramatic development, then rates declined through 2002 for all observed landscape changes except forest density decrease and tree mortality. Causes of landscape change included regional population growth, tourism demands, timber harvest for local use, fire suppression, bark beetle attack, and fuels reduction activities. Results from this study offer land managers within the Lake Tahoe basin and in similar regions a basis for making better informed land-use and management decisions to potentially minimize detrimental ecological impacts of landscape change. The perspective to be gained is based on quantitative retrospection of the effects of human-driven changes and the impacts of management action or inaction to the forested landscape. # 2008 Elsevier B.V. All rights reserved.

Demographic and land use dynamics have important implications for the natural environment within both developed and developing nations. Within the context of developed nations, popular and policy debates surrounding contemporary patterns of suburbanization attest to the salience of demographic and development issues. We examine the implications of land-use patterns as related to population and development within the context of the California Mojave Desert ecosystem. In a general sense, we aim to better understand the land require- ments inferred by varying levels of population growth and density, as well as the natural habitat implications of those requirements. We develop a GIS including remotely sensed imagery, and demographic, economic, and biophysical data to examine of the implications of various demographic scenarios on species diversity. Spatial and statistical models are designed to develop possible alternative land use 'futures'. Within the context of the California Mojave region, our results suggest that high-density development could reduce conflict with regions providing potential habitat for threatened or endangered species by over 80 percent. The pro- cess of model development demonstrates a potentially useful tool for policymakers, allowing for estimation and visualization of the land use implications of policy decisions.

The objective of this study was to directly detect impervious cover using new high-resolution IKONOS imagery in South Lake Tahoe, California, USA. The research presented was a pilot analysis to assess the ability of satellite imagery to derive accurate estimates of impervious cover, critical for assessing impacts to water quality, wildlife, and fish habitat. A combination of image processing methods based on principal component analysis and spatial morphological operators was developed for a 25 km2 urban area in the Lake Tahoe Basin. The methodology produced very accurate identification of both commercial and residential impervious cover in an area dominated by dense conifer canopy. Sub-canopy and sub-shadow surfaces were not only detectable, but also discernible with respect to the underlying substrate. An overall accuracy of 92.94% was obtained, with an even higher user accuracy of 95.83% based on 170 ground truth points. Impervious cover is a difficult feature to delineate accurately and efficiently us...

The increase in wildfires in arid and semi-arid parts of Nevada and elsewhere in the southwestern United States has implications for post-closure management and long-term stewardship for Soil Corrective Action Units (CAUs) on the Nevada National Security Site (NNSS) for which the Nevada Field Office of the United States Department of Energy, National Nuclear Security Administration has responsibility. For many CAUs and Corrective Action Sites, where closure-in-place alternatives are now being implemented or considered, there is a chance that these sites could burn over at some time while they still pose a risk to the environment or human health, given the long half lives of some of the radionuclide contaminants. This study was initiated to examine the effects and duration of wildfire on wind and water erodibility on sites analogous to those that exist on the NNSS. The data analyzed herein were gathered at the prescribed Gleason Fire site near Ely, Nevada, a site comparable to the northern portion of the NNSS. Quantification of wind erosion was conducted with a Portable In-Situ Wind ERosion Lab (PI-SWERL) on unburned soils, and on interspace and plant understory soils within the burned area. The PI-SWERL was used to estimate emissions of suspendible particles (particulate matter with aerodynamic diameters less than or equal to 10 micrometers) at different wind speeds. Filter samples, collected from the exhaust of the PI-SWERL during measurements, were analyzed for chemical composition. Based on nearly three years of data, the Gleason Fire site does not appear to have returned to pre burn wind erosion levels. Chemical composition data of suspendible particles are variable and show a trend toward pre-burn levels, but provide little insight into how the composition has been changing over time since the fire. Soil, runoff, and sediment data were collected from the Gleason Fire site to monitor the water erosion potential over the nearly three-year period. Soil hydrophobicity (water repellency) was noted on burned understory soils up to 12 months after the fire, as was the presence of ash on the soil surface. Soil deteriorated from a strong, definable pre-fire structure to a weakly cohesive mass (unstructured soil) immediately after the fire. Surface soil structure was evident 34 months after the fire at both burned and unburned sites, but was rare and weaker at burned sites. The amount of runoff and sediment was highly variable, but runoff occurred more frequently at burned interspace sites compared to burned understory and unburned interspace sites up to 34 months after the burn. No discernible pattern was evident on the amount of sediment transported, but the size of sediment from burned understory sites was almost double that of burned and unburned interspace soils after the fire, and decreased over the monitoring period. Curve numbers, a measure of the runoff potential, did not indicate any obvious runoff response to the fire. However, slight seasonal changes in curve numbers and runoff potential and, therefore, post-fire runoff response may be a function of fire impacts as well as the time of year that precipitation occurs. Site (interspace or understory) differences in soil properties and runoff persisted even after the fire. Vegetation data showed the presence of invasive grasses after the fire. Results from analysis of wind and water coupled with the spatial analysis of vegetation suggest that wind erosion may continue to occur due to the additional exposed soil surface (burned understory sites) until vegetation becomes re-established, and runoff may occur more frequently in interspace sites. The potential for fire-related wind erosion and water erosion may persist beyond three years in this system.

A historic return interval of 100 years for large fires in the U.S. southwestern deserts is being replaced by one where fires may reoccur as frequently as every 20 to 30 years. The shortened return interval, which translates to an increase in fires, has implications for management of Soil Corrective Action Units (CAUs) and Corrective Action Sites (CASs) for which the Department of Energy, National Nuclear Security Administration Nevada Field Office has responsibility. A series of studies was initiated at uncontaminated analog sites to better understand the possible impacts of erosion and transport by wind and water should contaminated soil sites burn. The first of these studies was undertaken at the Jacob Fire site approximately 12 kilometers (7.5 miles) north of Hiko, Nevada. A lightning-caused fire burned approximately 200 hectares during August 6-8, 2008. The site is representative of a transition between Mojave and Great Basin desert ecoregions on the Nevada National Security Site (NNSS), where the largest number of Soil CAUs/CASs are located. The area that burned at the Jacob Fire site was primarily a Coleogyne ramosissima (blackbrush) and Ephedra nevadensis (Mormon tea) community, also an abundant shrub assemblage in the similar transition zone on the NNSS. This report summarizes three years of measurements after the fire. Seven measurement campaigns at the Jacob Fire site were completed. Measurements were made on burned ridge (upland) and drainage sites, and on burned and unburned sites beneath and between vegetation. A Portable In-Situ Wind Erosion Lab (PI-SWERL) was used to estimate emissions of suspended particles at different wind speeds. Context for these measurements was provided through a meteorological tower that was installed at the Jacob Fire site to obtain local, relevant environmental parameters. Filter samples, collected from the exhaust of the PI-SWERL during measurements, were analyzed for chemical composition. Runoff and water erosion were quantified through a series of rainfall/runoff simulation tests in which controlled amounts of water were delivered to the soil surface in a specified amount of time. Runoff data were collected from understory and interspace soils on burned ridge and drainage areas. Runoff volume and suspended sediment in the runoff were sampled; the particle size distribution of the sediment was determined by laboratory analysis. Several land surface and soil characteristics associated with runoff were integrated by the calculation of site-specific curve numbers. Several vegetation surveys were conducted to assess post-burn recovery. Data from plots in both burned and unburned areas included species identification, counts, and location. Characterization of fire-affected area included measures at both the landscape scale and at specific sites. Although wind erosion measurements indicate that there are seasonal influences on almost all parameters measured, several trends were observed. PI-SWERL measurements indicated the potential for PM10 windblown dust emissions was higher on areas that were burned compared to areas that were not. Among the burned areas, understory soils in drainage areas were the most emissive, and interspace soils along burned ridges were least emissive. By 34 months after the burn (MAB), at the end of the study, emissions from all burned soil sites were virtually indistinguishable from unburned levels. Like the amount of emissions, the chemical signature of the fire (indicated by the EC-Soil ratio) was elevated immediately after the fire and approached pre-burn levels by 24 MAB. Thus, the potential for wind erosion at the Jacob Fire site, as measured by the amount and type of emissions, increased significantly after the fire and returned to unburned levels by 24 MAB. The effect of fire on the potential for water erosion at the Jacob Fire site was more ambiguous. Runoff and sediment from ridge interspace soils and unburned interspace soils were similar throughout the study period. Seldom, if ever, did runoff and sediment occur in burned drainage area soils. For burned soils where runoff occurred at 1 MAB, the sediment size was finer than on unburned sites, but this effect disappeared by 3 MAB. For the three year study under the conditions tested at the Jacob Fire site, the potential for water erosion appeared relatively unaffected by the fire. Vegetation responses were documented for each year following the fire. By the end of the study, there was a substantial difference in plant densities and richness between drainage and ridge sites. Cheatgrass densities were higher in unburned plots, and cheatgrass was also more dominant in the community composition in unburned plots. Cheatgrass had increased in the burned area but so did other native species. Three years after the fire, the burned landscape continued to revegetate but had yet to approximate the condition of an unburned landscape. The results from the vegetation surveys support the wind erosion results, where the primary source of windborne particles originate from the understory, where lower plant diversity and densities were found. The soil appears to be more resilient and have a much shorter recovery time than the vegetation in this particular community.

Landsat Thematic Mapper (TM) data were used to characterize the extent and intensity of coastal forest damage resulting from Hurricane Hugo (September 22, 1989) at Hobcaw Barony, South Carolina, USA. Low altitude vertical color infrared aerial photography and field observations provided the ground truth data necessary for validation. Bands 4 (0.76 ‐ 0.90 μm) and 7 (2.08 ‐ 2.35 μm) and three unsupervised classification techniques were used for forest damage classification of an image immediately following Hurricane Hugo. Similarly, a ratio of bands 7/4 was used as an index for mapping wind and storm surge damage and for change detection. The three unsupervised classification methods and the change detection analysis were effective at identifying the extent of forest damage. Healthy and heavily damaged stands were identified most accurately. Classification of damage intensity, especially for intermediate levels of damage, was more difficult and was affected by soil characteristics and understory ve...

In the hydrologic approach developed by French et al. (2005) to estimate the 100-year regulatory floodplain on a playa lake, it was conservatively assumed that precipitation varies with elevation but is otherwise uniform over the entire contributing watershed. In this follow-on study, Doppler radar (WSR-88D) precipitation estimates were used to incorporate spatial variability of precipitation and to validate the approach for the Rogers Lake watershed in the California Mojave Desert, USA. Accurate runoff estimates are necessary to manage mission activities for Edwards Air Force Base, which lies within this watershed, because Rogers (dry) Lake playa is used as an active runway. Radar-measured storm events were analyzed using the French et al. (2005) approach and the modeled volume of runoff reaching Rogers Lake was compared to its inundation calculated based on corresponding Landsat satellite imagery and airborne LiDAR high spatial resolution digital elevation model (DEM) data of the lakebed. Model results both under- and over-estimated playa inundations compared to the image based DEM calculations for each of the two storm events analyzed. Possible explanations of the differences include: (1) poor representation of ground level precipitation provided by the Doppler data; (2) over or underestimation of water via image interpretation; (3) inappropriate estimation of the watershed hydrologic parameters ( e.g. , infiltration); (4) error associated with the data sources, particularly in the DEM; and (5) a combination of one or more of these factors.

The use of detector dogs has been demonstrated to be effective and safe for finding Mojave desert tortoises and provides certain advantages over humans in field surveys. Unlike humans who rely on visual cues for target identification, dogs use primarily olfactory cues and can therefore locate targets that are not visually obvious. One of the key benefits of surveying with dogs is their efficiency at covering ground and their ability to detect targets from long distances. Dogs may investigate potential targets using visual cues but confirm the presence of a target based on scent. Everything that emits odor does so via vapor-phase molecules and the components comprising a particular scent are carried primarily though bulk movement of the atmosphere. It is the ability to search for target odor and then go to its source that makes dogs ideal for rapid target recognition in the field setting. Using tortoises as targets, we quantified distances that dogs detected tortoise scent, followed it to source, and correctly identified tortoises as targets. Detection distance data were collected during experimental trials with advanced global positioning system (GPS) technology and then analyzed using geographic information system (GIS) modeling techniques. Detection distances ranged from 0.5 m to 62.8 m for tortoises on the surface. We did not observe bias with tortoise size, age class, sex or the degree to which tortoises were handled prior to being found by the dogs. The methodology we developed to quantify olfaction-based detection distance using dogs can be applied to other targets that dogs are trained to find.

The desert tortoise (Gopherus agassizii) is federally listed as "threatened" and is afforded protection in several U.S. states including California, Nevada, Utah, and Arizona. Numerous factors ranging from habitat destruction to disease are thought to contribute to the species' decline throughout its range. Data collection on desert tortoises in the wild is challenging because tortoises are secretive, and many age and size classes are virtually undetectable in the wild. Detection dogs have been used for decades to assist humans, and the use of dogs for wildlife surveys is of increasing interest to scientists and wildlife managers. To address the basic question of whether dogs could be used to survey for the desert tortoise, we quantified the reliability and efficacy of dogs trained for this purpose. Efficacy is the number of tortoises that dogs find out of a known population. Reliability is a measure of how many times a dog performs its trained alert when it has found a tortoise. A series of experimental trials were designed to statistically quantify these metrics in the field setting where dogs trained to locate live desert tortoises were tested on their ability to find them on the surface, in burrows, and in mark-recapture surveys. Results indicated that dogs are effective at and can safely locate desert tortoises with reliability on the surface and are capable of detecting tortoises in burrows under a range of environmental conditions. Dogs found tortoises at the same statistical rate at temperatures between 12 degrees and 27 degrees C, relative humidity from 16% to 87%, and wind speeds up to 8 m/s. In both surface and burrow trials, dogs found >90% of the experimental animals. In comparative studies with humans, dogs found tortoises as small as 30 mm, whereas the smallest tortoise located by human survey teams was 110 mm. Although not all dogs or dog teams meet the requirements to conduct wildlife surveys, results from this study show the promise in using dogs to increase our knowledge of rare, threatened, and endangered species through improved data collection methods.