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USGS2012

A simple method for estimating basin-scale groundwater discharge by vegetation in the basin and range province of Arizona using remote sensing information and geographic information systems

Groundwater is a vital water resource in the arid to semi-arid southwestern United States. Accurate accounting of inflows to and outflows from the groundwater system is necessary to effectively manage this shared resource, including the important outflow component of groundwater discharge by vegetation. A simple method for estimating basin-scale groundwater discharge by vegetation is presented that uses remote sensing data from satellites, geographic information systems (GIS) land cover and stream location information, and a regression equation developed within the Southern Arizona study area relating the Enhanced Vegetation Index from the MODIS sensors on the Terra satellite to measured evapotranspiration. Results computed for 16-day composited satellite passes over the study area during the 2000 through 2007 time period demonstrate a sinusoidal pattern of annual groundwater discharge by vegetation with median values ranging from around 0.3 mm per day in the cooler winter months to around 1.5 mm per day during summer. Maximum estimated annual volume of groundwater discharge by vegetation was between 1.4 and 1.9 billion m 3 per year with an annual average of 1.6 billion m 3 . A simplified accounting of the contribution of precipitation to vegetation greenness was developed whereby monthly precipitation data were subtracted from computed vegetation discharge values, resulting in estimates of minimum groundwater discharge by vegetation. Basin-scale estimates of minimum and maximum groundwater discharge by vegetation produced by this simple method are useful bounding values for groundwater budgets and groundwater flow models, and the method may be applicable to other areas with similar vegetation types.

Arizona↗

USGS2012

Constancy of local spread rates for buffelgrass (Pennisetum ciliare L.) in the Arizona Upland of the Sonoran Desert

In North American deserts, grass invasions threaten native vegetation via competition and altered fire regimes. Accurate prediction and successful mitigation of these invasions hinge on estimation of spread rates and their degree of constancy in time and space. We used high-resolution aerial photographs from 11 sites in the Santa Catalina Mountains, southern Arizona to reconstruct the spread of buffelgrass ( Pennisetum ciliare ), a C4 perennial bunchgrass, since 1980. The total area infested was fit to a logistic model and residuals of the model were compared to climatic factors of the corresponding and lagged time periods. Infestations grew from small colonizing patches in the 1980s to 66 ha in 2008, doubling every 2.26–7.04 years since 1988. Although buffelgrass germination, establishment and distribution are favored by wet summers and warm winters, climate variables did not predict spread rates. Buffelgrass has grown at a constant rate, at least since 1988, when much of its expansion took place. In the study area, minimum requirements are met almost every year for germination and reproduction, establishing a consistent baseline for spread that manifests as a constant spread rate.

Sonoran Desert;Arizona Upland↗

USGS2013

Regional demographic trends from long-term studies of saguaro ( Carnegiea gigantea ) across the northern Sonoran Desert

Ten saguaro ( Carnegiea gigantea ) populations in the northern Sonoran Desert were monitored from 1959 to 2005 to discriminate how climate influences plant growth, abundance, reproductive potential, survivorship, age structure and regeneration trends. Thousands of saguaros were measured to determine site-specific growth rates and survivorship through time. Observed growth rates were used to predict the ages of saguaros and reconstruct local and regional regeneration patterns back to the late 18th century. Both growth rates and degree of branching generally tracked temperature and moisture gradients. Site-specific age-height models explained 89-97% of variance in observed ages, with a slope of nearly one. Regeneration was more consistent at sites in the western (hotter/drier) than eastern (cooler/wetter) sites, which exhibited clear multidecadal variability in regeneration rates. Averaged across the region, saguaro regeneration rates were highest from 1780 to 1860, coincident with wet conditions and high Pinus ponderosa recruitment in the highlands. Milder and wetter winters and protection from livestock grazing likely promoted late 20th century regeneration surges at some sites. Predictions of saguaro population dynamics in the 21st century likely will be confounded by the saguaro's episodic and asynchronous regeneration, continued urbanization, ongoing grass invasions and associated wildfires, and changing climate.

Arizona↗

USGS2013

Plot- and landscape-level changes in climate and vegetation following defoliation of exotic saltcedar (Tamarix sp.) from the biocontrol agent Diorhabda carinulata along a stream in the Mojave Desert (USA)

The biocontrol agent, northern tamarisk beetle (Diorhabda carinulata), has been used to defoliate non-native saltcedar (Tamarix spp.) in USA western riparian systems since 2001. Biocontrol has the potential to impact biotic communities and climatic conditions in affected riparian areas. To determine the relationships between biocontrol establishment and effects on vegetation and climate at the plot and landscape scales, we measured temperature, relative humidity, foliage canopy, solar radiation, and used satellite imagery to assess saltcedar defoliation and evapotranspiration (ET) along the Virgin River in the Mojave Desert. Following defoliation solar radiation increased, daily humidity decreased, and maximum daily temperatures tended to increase. MODIS and Landsat satellite imagery showed defoliation was widespread, resulting in reductions in ET and vegetation indices. Because biocontrol beetles are spreading into new saltcedar habitats on arid western rivers, and the eventual equilibrium between beetles and saltcedar is unknown, it is necessary to monitor trends for ecosystem functions and higher trophic-level responses in habitats impacted by biocontrol.

Mojave Desert↗

USGS2013

Vegetation impoverishment despite greening: a case study from central Senegal

Recent remote sensing studies have documented a greening trend in the semi-arid Sahel and Sudan zones of West Africa since the early 1980s, which challenges the mainstream paradigm of irreversible land degradation in this region. What the greening trend means on the ground, however, has not yet been explored. This research focuses on a region in central Senegal to examine changes in woody vegetation abundance and composition in selected sites by means of a botanical inventory of woody vegetation species, repeat photography, and perceptions of local land users. Despite the greening, an impoverishment of the woody vegetation cover was observed in the studied sites, indicated by an overall reduction in woody species richness, a loss of large trees, an increasing dominance of shrubs, and a shift towards more arid-tolerant, Sahelian species since 1983. Thus, interpretation of the satellite-derived greening trend as an improvement or recovery is not always justified. The case of central Senegal represents only one of several possible pathways of greening throughout the region, all of which result in similar satellite-derived greening signals.

Journal of Arid Environments↗

USGS2013

Grazing effects on aboveground primary production and root biomass of early-seral, mid-seral, and undisturbed semiarid grassland

Annual/perennial and tall/short plant species differentially dominate early to late successional shortgrass steppe communities. Plant species can have different ratios of above-/below-ground biomass distributions and this can be modified by precipitation and grazing. We compared grazing effects on aboveground production and root biomass in early- and mid-seral fields and undisturbed shortgrass steppe. Production averaged across four years and grazed and ungrazed treatments were 246, 134, and 102 g m −2 yr −1 for the early-, mid-seral, and native sites, respectively, while root biomass averaged 358, 560, and 981 g m −2 , respectively. Early- and mid-seral communities provided complimentary forage supplies but at the cost of root biomass. Grazing increased, decreased, or had no effect on aboveground production in early-, mid-seral, and native communities, and had no effect on roots in any. Grazing had some negative effects on early spring forage species, but not in the annual dominated early-seral community. Dominant species increased with grazing in native communities with a long evolutionary history of grazing by large herbivores, but had no effects on the same species in mid-seral communities. Effects of grazing in native communities in a region cannot necessarily be used to predict effects at other seral stages.

Journal of Arid Environments↗

USGS2013

Controls of biological soil crust cover and composition shift with succession in sagebrush shrub-steppe

Successional stage may determine strength and causal direction of interactions among abiotic and biotic factors; e.g., species that facilitate the establishment of other species may later compete with them. We evaluated multivariate hypotheses about abiotic and biotic factors shaping biological soil crusts (BSCs) in early and late successional stages. We surveyed vegetation and BSC in the shrub-steppe ecosystem of the Columbia Basin. We analyzed the relationships with bryophyte and lichen covers using structural equation models, and analyzed the relationships with BSC composition using Indicator Species Analysis and distance-based linear models. Cover, indicator species, and composition varied with successional stage. Increasing elevation and bryophyte cover had higher lichen cover early in succession; these relationships were negative in the later successional stage. Lichen cover did not appear to impede B. tectorum cover, but B. tectorum appeared to strongly negatively affect lichen cover in both stages. Biological soil crust composition varied with bunchgrass cover in the early successional stage, but with elevation and B. tectorum cover later in succession. Our findings support the hypotheses that as succession progresses, the strength and direction of certain community interactions shift, and B. tectorum leads to reductions in biological soil crust cover regardless of successional stage.

Journal of Arid Environments↗

USGS2013

Nest site characteristics and nesting success of the Western Burrowing Owl in the eastern Mojave Desert

We evaluated nest site selection at two spatial scales (microsite, territory) and reproductive success of Western Burrowing Owls ( Athene cunicularia hypugaea ) at three spatial scales (microsite, territory, landscape) in the eastern Mojave Desert. We used binary logistic regression within an information-theoretic approach to assess factors influencing nest site choice and nesting success. Microsite-scale variables favored by owls included burrows excavated by desert tortoise ( Gopherus agassizii ), burrows with a large mound of excavated soil at the entrance, and a greater number of satellite burrows within 5 m of the nest burrow. At the territory scale, owls preferred patches with greater cover of creosote bush ( Larrea tridentata ) within 50 m of the nest burrow. An interaction between the presence or absence of a calcic soil horizon layer over the top of the burrow (microsite) and the number of burrows within 50 m (territory) influenced nest site choice. Nesting success was influenced by a greater number of burrows within 5 m of the nest burrow. Total cool season precipitation was a predictor of nesting success at the landscape scale. Conservation strategies can rely on management of habitat for favored and productive nesting sites for this declining species.

Arizona;Nevada↗

USGS2013

Floral ecology and insect visitation in riparian Tamarix sp. (saltcedar)

Climate change projections for semiarid and arid North America include reductions in stream discharge that could adversely affect riparian plant species dependent on stream-derived ground water. In order to better understand this potential impact, we used a space-for-time substitution to test the hypotheses that increasing depth-to-groundwater (DGW) is inversely related to Tamarix sp. (saltcedar) flower abundance (F) and nectar production per flower (N). We also assessed whether DGW affected the richness or abundance of insects visiting flowers. We examined Tamarix floral attributes and insect visitation patterns during 2010 and 2011 at three locations along a deep DWG gradient (3.2–4.1 m) on a floodplain terrace adjacent to Las Vegas Wash, an effluent-dominated Mojave Desert stream. Flower abundance and insect visitation patterns differed between years, but no effect from DGW on either F or N was detected. An eruption of a novel non-native herbivore, the splendid tamarisk weevil (Coniatus splendidulus), likely reduced flower production in 2011.

Journal of Arid Environments↗

USGS2013

Disruption rates for one vulnerable soil in Organ Pipe Cactus National Monument, Arizona, USA

Rates of soil disruption from hikers and vehicle traffic are poorly known, particularly for arid landscapes. We conducted an experiment in Organ Pipe Cactus National Monument (ORPI) in western Arizona, USA, on an air-dry very fine sandy loam that is considered to be vulnerable to disruption. We created variable-pass tracks using hikers, an all-terrain vehicle (ATV), and a four-wheel drive vehicle (4WD) and measured changes in cross-track topography, penetration depth, and bulk density. Hikers (one pass = 5 hikers) increased bulk density and altered penetration depth but caused minimal surface disruption up to 100 passes; a minimum of 10 passes were required to overcome surface strength of this dry soil. Both ATV and 4WD traffic significantly disrupted the soil with one pass, creating deep ruts with increasing passes that rendered the 4WD trail impassable after 20 passes. Despite considerable soil loosening (dilation), bulk density increased in the vehicle trails, and lateral displacement created berms of loosened soil. This soil type, when dry, can sustain up to 10 passes of hikers but only one vehicle pass before significant soil disruption occurs; greater disruption is expected when soils are wet. Bulk density increased logarithmically with applied pressure from hikers, ATV, and 4WD.

Arizona↗

USGS2013

Effects of natural flooding and manual trapping on the facilitation of invasive crayfish-native amphibian coexistence in a semi-arid perennial stream

Aquatic amphibians are known to be vulnerable to a myriad of invasive predators. Invasive crayfish are thought to have eliminated native populations of amphibians in some streams in the semi-arid Santa Monica Mountains of southern California. Despite their toxic skin secretions that defend them from native predators, newts are vulnerable to crayfish attacks, and crayfish have been observed attacking adult newts, and eating newt egg masses and larvae. For 15 years, we have observed invasive crayfish and native California newts coexisting in one stream in the Santa Monica Mountains. During that period, we monitored the densities of both crayfish and newt egg mass densities and compared these to annual rainfall totals. After three seasons of below average rainfall, we reduced crayfish numbers by manual trapping. Our long-term data indicated that crayfish did not fare well in years when rainfall is above the historic average. This invasive predator did not evolve with high velocity streams, and observations indicated that southern California storm events washed crayfish downstream, killing many of them. Newts exhibit increased reproduction in years when crayfish numbers were reduced. A comparison with a nearby stream that does not contain crayfish indicated that newt reproduction positively responded to increased rainfall, but that fluctuations were much greater in the stream that contains crayfish. We suggest that rainfall patterns help explain invasive crayfish/newt coexistence and that management for future coexistence may benefit from manual trapping.

Journal of Arid Environments↗

USGS2014

Pedological and geological relationships with soil lichen and moss distribution in the eastern Mojave Desert, CA, USA

Biological soil crusts (biocrusts) are ubiquitous in drylands globally. Lichens and mosses are essential biocrust components and provide a variety of ecosystem services, making their conservation and management of interest. Accordingly, understanding what factors are correlated with their distribution is important to land managers. We hypothesized that cover would be related to geologic and pedologic factors. We sampled 32 sites throughout the eastern Mojave Desert, stratifying by parent material and the age of the geomorphic surfaces. The cover of lichens and mosses on ‘available ground’ (L + M av ; available ground excludes ground covered by rocks or plant stems) was higher on limestone and quartzite-derived soils than granite-derived soils. Cover was also higher on moderately younger-aged geomorphic surfaces (Qya2, Qya3, Qya4) and cutbanks than on very young (Qya1), older-aged surfaces (Qia1, Qia2), or soils associated with coppice mounds or animal burrowing under Larrea tridentata. When all sites and parent materials were combined, soil texture was the most important factor predicting the occurrence of L + M av , with cover positively associated with higher silt, very fine sand, and fine sand fractions and negatively associated with the very coarse sand fraction. When parent materials were examined separately, nutrients such as available potassium, iron, and calcium became the most important predictors of L + M av cover.

California↗

USGS2014

Insights for empirically modeling evapotranspiration influenced by riparian and upland vegetation in semiarid regions

Water resource managers aim to ensure long-term water supplies for increasing human populations. Evapotranspiration (ET) is a key component of the water balance and accurate estimates are important to quantify safe allocations to humans while supporting environmental needs. Scaling up ET measurements from small spatial scales has been problematic due to spatiotemporal variability. Remote sensing products provide spatially distributed data that account for seasonal climate and vegetation variability. We used MODIS products [i.e., Enhanced Vegetation Index (EVI) and nighttime land surface temperatures (LST n )] to create empirical ET models calibrated using measured ET from three riparian-influenced and two upland, water-limited flux tower sites. Results showed that combining all sites introduced systematic bias, so we developed separate models to estimate riparian and upland ET. While EVI and LST n were the main drivers for ET in riparian sites, precipitation replaced LST n as the secondary driver of ET in upland sites. Riparian ET was successfully modeled using an inverse exponential approach (r 2 = 0.92) while upland ET was adequately modeled using a multiple linear regression approach (r 2 = 0.77). These models can be used in combination to estimate ET at basin scales provided each region is classified and precipitation data is available.

Arizona↗

USGS2014

Common raven occurrence in relation to energy transmission line corridors transiting human-altered sagebrush steppe

Energy-related infrastructure and other human enterprises within sagebrush steppe of the American West often results in changes that promote common raven ( Corvus corax ; hereafter, raven) populations. Ravens, a generalist predator capable of behavioral innovation, present a threat to many species of conservation concern. We evaluate the effects of detailed features of an altered landscape on the probability of raven occurrence using extensive raven survey ( n = 1045) and mapping data from southern Idaho, USA. We found nonlinear relationships between raven occurrence and distances to transmission lines, roads, and facilities. Most importantly, raven occurrence was greater with presence of transmission lines up to 2.2 km from the corridor.We further explain variation in raven occurrence along anthropogenic features based on the amount of non-native vegetation and cover type edge, such that ravens select fragmented sagebrush stands with patchy, exotic vegetative introgression. Raven occurrence also increased with greater length of edge formed by the contact of big sagebrush ( Artemisia tridentate spp.) with non-native vegetation cover types. In consideration of increasing alteration of sagebrush steppe, these findings will be useful for planning energy transmission corridor placement and other management activities where conservation of sagebrush obligate species is a priority.

Idaho↗

USGS2015

Ungulate exclusion, conifer thinning and mule deer forage in northeastern New Mexico

The southwestern United States has experienced expansion of conifer species ( Juniperus spp. and Pinus ponderosa ) into areas of semi-arid grassland over the past century. The expansion of conifers can limit palatable forage and reduce grass and forb communities. Conifer species are sometimes thinned through hydraulic mulching or selective cutting. We assessed the effects of these treatments on mule deer ( Odocoileus hemionus ) habitat in northeastern New Mexico to determine if conifer thinning improved cover of preferred forage species for mule deer in areas with and without ungulates. We measured plant cover and occurrence of preferred forage species in the summers of 2011 and 2012. An ongoing regional drought probably reduced vegetation response, with preferred forage species and herbaceous cover responding to conifer thinning or ungulate exclusion immediately following treatment, but not the following year. In 2011, areas that received thinning treatments had a higher abundance of preferred forage when compared to sites with no treatment. Grass coverage exhibited an immediate response in 2011, with ungulate exclosures containing 8% more coverage than areas without exclosures. The results suggest that conifer thinning and ungulate exclusion may elicit a positive response, however in the presence of drought; the positive effects are only short-term.

New Mexico↗

USGS2015

Wide-area ratios of evapotranspiration to precipitation in monsoon-dependent semiarid vegetation communities

Evapotranspiration (ET) and the ratio of ET to precipitation (PPT) are important factors in the water budget of semiarid rangelands and are in part determined by the dominant plant communities. Our goal was to see if landscape changes such as tree or shrub encroachment and replacement of native grasses by invasive grasses impacted ET and ET/PPT and therefore watershed hydrology in this biome. We determined ET and ET/PPT for shrublands, grasslands and mesquite savannas in southern Arizona at five moisture flux towers and determined the environmental factors controlling ET in each plant community. We then scaled ET over areas of 4–36 km 2 , representing homogeneous patches of each plant community, using the Enhanced Vegetation Index (EVI) from MODIS sensors on the Terra satellite. Over wide areas, estimated ET/PPT projected from MODIS EVI ranged from 0.71 for a sparsely-vegetated shrub site to 1.00 for grasslands and mesquite savannas. The results did not support hypotheses that encroachment of mesquites into grasslands or that replacement of native grasses with introduced Eragrostis lehmanniana (lehmann lovegrass) have increased rangeland ET.

Arizona↗

USGS2015

Hydroecological condition and potential for aquaculture in lakes of the arid region of Khorezm, Uzbekistan

With >400 small (<1 ha) lakes, the arid Khorezm Province in Uzbekistan may be well-suited for aquaculture production. Developing water resources to provide a local food supply could increase fish consumption while improving the rural economy. Hydroecological (biological and physical) and chemical characteristics (including legacy pesticides ΣDDT and ΣHCH) of four representative drainage lakes in Khorezm from 2006 to 2008 were analyzed for the lakes’ capability to support healthy fish populations. Lake characteristics were categorized as “optimal” (having little or no effect on growth and development), “tolerable” (corresponding to chronic or sub-lethal toxicity) and “lethal” (corresponding to acute toxicity). Results indicate that three lakes are likely well-suited for raising fish species, with water quality meeting World Bank aquaculture guidelines. However, the fourth lake often had salinity concentrations > optimal levels for local fish species. Pesticide concentrations in water of all four lakes were within tolerable aquaculture ranges. Although water ΣDDT concentrations were >optimal limits, results from chemical analysis of fish tissues and semi-permeable membrane devices indicated that study lake ΣDDT concentrations were not accumulating in fish or posing a human health threat. Land and water management to maintain adequate lake water quality are imperative for sustaining fish populations for human consumption.

Khorezm↗

USGS2015

Bidirectional recovery patterns of Mojave Desert vegetation in an aqueduct pipeline corridor after 36 years: I. Perennial shrubs and grasses

We studied recovery of 21 perennial plant species along a severely disturbed aqueduct corridor in a Larrea tridentata - Ambrosia dumosa plant alliance in the Mojave Desert 36 years after construction. The 97-m wide corridor contained a central dirt road and buried aqueduct pipeline. We established transects at 0 m (road verge), 20 m and 40 m into the disturbance corridor, and at 100 m in undisturbed habitat (the control). Although total numbers of shrubs per transect did not vary significantly with distance from the verge, canopy cover of shrubs, species richness, and species diversity were higher in the control than at the verge and other distances. Canopy cover of common shrubs ( Ericameria nauseosa, Ambrosia salsola, A. dumosa, L. tridentata, Grayia spinosa ) and perennial grasses ( Elymus elymoides, Poa secunda ) also varied significantly by location. Discriminant analysis clearly separated the four distances based on plant composition. Patterns of recovery were bidirectional: secondary succession from the control into the disturbance corridor and inhibition from the verge in the direction of the control. Time estimated for species composition to resemble the control is dependent on location within the disturbance corridor and could be centuries at the road verge. Our findings have applications to other deserts.

California↗