Thesis (Ph. D.)--Texas State University--San Marcos, 2009. / Vita. Appendices: leaves 157-171. Includes bibliographical references (leaves 172-185). Also available on microfilm.

The Northern tamarisk beetle (Diorhabda carinulata) was introduced to the Colorado River Basin in 2004 as a biological control agent for the invasive shrub: tamarisk (Tamarix spp.). Since 2004, D. carinulata has colonized much of the Colorado River Basin, defoliating tamarisk and adapting to local abiotic cues as it has spread across the landscape. I studied the interplay of abiotic cues, tamarisk defoliation, and the population dynamics of D. carinulata along portions of the Colorado, Dolores, and San Juan rivers from 2007-2012. My results suggest that the timing and location of tamarisk defoliation can be predicted based on the abiotic cues of a location (specifically temperature and day length) and the spatial distribution of D. carinulata across the landscape. In contrast, I also found that the spatial distribution of D. carinulata was often a result of D. carinulata abandoning areas where it had defoliated tamarisk at high intensities. I found that larval abundances from the first new generation of D. carinulata produced in a year were positively linearly correlated with defoliation intensities one month later. Comparatively, generations of larvae produced later in the season were correlated with defoliation intensity along a bell curve, in which the number of D. carinulata declined in areas>50% defoliated. The timing of defoliation during the active season was correlated with the arrival of each new generation of larvae. I found the number of generations of D. carinulata produced in a year varied based on spring temperatures and fall day lengths. The timing of when spring temperatures rose above 15°C dictated when D. carinulata could begin reproductive activity, and this in turn resulted in how early in the year tamarisk could become defoliated. Day length cues governing overwintering in D. carinulata appear to have shortened by>30 min. compared to populations of D. carinulata first released in North America in 2001, resulting in longer duration of activity into the fall. We found the range of D. carinulata could grow as much as 62.8±5.6 km in a year along a linear riparian system, and populations of D. carinulata could defoliate between 24±11.2 and 116±11.2 km of river corridor tamarisk in a year.

Thesis (Ph. D.)--University of Texas at El Paso, 2009. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

This research focused on estimating evapotranspiration (i.e., the amount of water vaporizing into the atmosphere through processes of surface evaporation and plant transpiration) under both theoretical and actual conditions. There were two study areas involved: one, on a large scale where 704 agriculturally-representative, electronic weather stations were used to evaluate the drivers and calculated reference evapotranspiration of a NASA gridded weather forcing model in the 17 western states in the contiguous U.S.; and two, transpiration of invasive saltcedar (Tamarix sp.) in the floodplain of the lower Colorado River, California, with Bowen ratio, eddy covariance, and groundwater fluxes. In this study, a fire destroyed the saltcedar forest, which allowed comparison of evapotranspiration before and after\ this event Comparison of the input weather parameters showed some variance between the electronic weather stations and the gridded model, but calculated reference evapotranspiration performed well by relying on the better input and more highly weighed variables of air temperature and downward shortwave radiation. Only in the southern portions of California, Arizona, and New Mexico were the evapotranspiration estimates using the gridded dataset not well correlated with the electronic weather stations and not recommended for prediction. Saltcedar evapotranspiration was found to match more recent and conservative estimates for the phreatophyte than what was historically portrayed in the literature. Horizontal advection from the surrounding desert was also observed to affect the riparian energy balance. Annual average total evapotranspiration before a fire varied from 0.60-1.44 meters/year to 0.25-1.00 meters/year post fire.

Master of Science / Department of Biology / Jesse B. Nippert / In 1902, President Theodore Roosevelt signed and enacted the Reclamation Act, which would fundamentally alter the lowland hydrology of the arid southwest over the next century. Flow regulations, groundwater pumping, damming, and river channel changes have led to decreases in water table heights and periodic overbank flooding, and subsequently, increased soil salinity in the arid Southwest. During this period, native riparian tree species have declined significantly and an invasive tree species, Tamarix ramosissima, has increased in abundance and distribution. Increases in soil salinity negatively impact the physiology of native riparian tree species, but the impacts of soil salinity on Tamarix physiology are incompletely known. I studied the impact of increasing soil salinities on the physiology of Tamarix in both field and controlled environments. I first studied the impacts of increasing soil salinities on Tamarix physiology at two semi-arid sites in western Kansas. I concluded that physiological functioning in Tamarix was maintained across a soil salinity gradient from 0 to 14,000 ppm illustrating robust physiological responses. Using cuttings from Tamarix trees at both sites, I subjected plants to higher NaCl concentrations (15,000 and 40,000 ppm). Tamarix physiology was decreased at 15,000 ppm and 40,000 ppm. Tamarix physiological functioning was affected at the induction of treatments, but acclimated over 30-40 days. These results reveal a threshold salinity concentration at which Tamarix physiological functioning decreases, but also illustrate the advantageous halophytic nature of Tamarix in these saline environments. Many arid and semi-arid environments are predicted to become more saline, however, results from both studies suggest that increasing salinity will not be a major barrier for Tamarix persistence and range expansion in these environments.

abstract: Non-native saltcedar (Tamarix spp.) has invaded many riparian communities and is the third most abundant tree in Southwestern riparian areas. I evaluated lizard populations and microhabitat selection during 2009 and 2010 along the Virgin River in Nevada and Arizona to determine the impact of saltcedar. Along the riparian corridor, I observed common side-blotched lizards (Uta stansburiana) within two vegetation types: monotypic non-native saltcedar stands or mixed stands of cottonwood (Populus fremontii), willow (Salix spp.), mesquite (Prosopis spp.) and saltcedar. I predicted that population parameters such as body condition, adult to hatchling ratio, abundance, and persistence would vary among vegetation types. Also, I predicted the presence of saltcedar influences how lizards utilize available habitat. Lizard population parameters were obtained from a mark-recapture study in which I captured 233 individual lizards. I examined habitat selection and habitat availability using visual encounter surveys (VES) for lizards and recorded 11 microhabitat variables where 16 lizards were found. I found no significant difference in population parameters between mixed and non-native saltcedar communities. However, population parameters were negatively correlated with canopy cover. I found that lizards selected habitat with low understory and canopy cover regardless of vegetation type. My results indicate that lizards utilize similar structural characteristics in both mixed and non-native vegetation. Understanding impacts of saltcedar on native fauna is important for managers who are tasked with control and management of this non-native species. / Dissertation/Thesis / M.S. Applied Biological Sciences 2011

abstract: Riparian areas are an important resource, especially in the arid southwest, for many wildlife species. Understanding species occurrence in areas dominated by non-native vegetation is important to determine if management should be implemented. Saltcedar (Tamarix spp.) is one of the most prevalent non-native trees in riparian areas in the southwest United States and can alter vegetation structure, but little is known about how medium and large carnivores use stands of saltcedar. Three riparian forest types make up the San Pedro riparian corridor: non-native saltcedar, native mesquite (Prosopis spp.) bosque, and a mixture of native cottonwood (Populus fremontii) and willow (Salix goodingii) woodlands. My goals were to determine relative use, diversity, and occupancy of medium and large mammals across forest types to evaluate use of the non-native stands. I sampled mammals along approximately 25.7 river kilometers between July 2017 and October 2018, using 18 trail cameras (six per forest type) spaced 1km apart. I summarized environmental variables around the camera sites to relate them to species occupancy and reduced them to 4 components using a Principal Component Analysis (PCA). I observed 14 carnivore species, including bobcat (Lynx rufus), coyote (Canis latrans), and coati (Nasua narica) over 7,692 trap nights. Occupancy of some species may have been influenced by the different components, but models showed high standard errors, making it difficult to draw firm conclusions. Most mammal species used all three forest types at some level and no surveyed forest type was completely avoided or unused. Coyote tended to have greater use in the mesquite forest while canids trended toward greater use in saltcedar forest. Based on two-species occupancy models as well as activity overlap patterns, subordinate species did not appear to avoid dominant species. No species seems significantly affected by non-native saltcedar at this time. / Dissertation/Thesis / Masters Thesis Biology 2019

Four closely related species of leaf beetles (Diorhabda spp.; Coleoptera:Chrysomelidae) have been introduced into the western United States as biocontrol agents for the invasive Eurasian shrub tamarisk (Tamarix spp.; Violales:Tamaricaceae). These beetles have since continued to spread and establish throughout the western United States. Another exotic insect, the tamarisk leafhopper (Opsius stactogalus, Fieber;Hemiptera: Cicadellidae), had previously become established in these areas and now shares tamarisk as a host plant with the beetles. To assess more carefully the potential for interactions between leafhoppers and beetles, field censuses and cage studies were conducted to determine the phenologies and potential interactions of O. stactogolus and D. carinulata when attacking Tamarix ramosissima (Ledebour) in western Colorado. The leafhopper underwent development through at least three generations per season, whereas the beetle was shown to develop through two generations per season. Variation in leafhopper abundance was associated with the extent and type of foliar damage to tamarisk trees. Individual trees with greatest D. carinulata abundances and subsequent defoliation had significantly reduced O. stactogalus abundances thereafter. Abundance of O. stactogalus was also shown to vary significantly among tamarisk plants in cage settings where leafhoppers were given the choice of potted tamarisk plants with ~50% damage to foliage from D. carinulata versus undamaged plants. In contrast, D. carinulata abundance was not shown to differ strongly in response to O. stactogalus damage in the field or in cage experiments. Field results across sites, however, showed similar trends of reduced beetle abundance on plants more heavily attacked by leafhoppers, and larval growth tests suggested slight reductions in larval pupation and adult emergence of D. carinulata when grown on O. stactogalus-damaged tamarisk. It is not clear if slight tendencies in D. carinulata abundance along with much stronger responses in O. stactogalus abundance were the result of limited plant material, rather than an induced plant defense. It is clear, however, that these specialist herbivores are interacting in an asymmetric competitive fashion while feeding on the same host plant.

abstract: Riparian systems in the arid southwest are heavily altered and, based on relative land-area, provision a disproportionately high number of native wildlife. Amphibians and reptiles are collectively the most threatened vertebrate taxa and, in the Sonoran Desert, are often reliant on riparian habitat. The link between amphibians and environmental water characteristics, as well as the association between lizards and habitat structure, make herpetofauna good organisms for which to examine the effects of environmental change. My objective was to relate capture rates of a fossorial anuran and lizard abundance to aspects of native, invaded, and shrub-encroached riparian habitats in order to forecast the potential winners and losers of riparian habitat xerification and invasion. I measured habitat and monitored herpetofauna at 18 sites near the confluence of the San Pedro River and Gila River in Pinal County, Arizona in 2016 and 2017. Sites were divided into three categories based on dominant tree genus; Populus-Salix, Prosopis, and Tamarix, which represented native riparia, xeric riparia, and invaded riparia, respectively. Habitat measurements indicated that sites varied significantly in structure, and that dominant tree species was a useful descriptor of habitat physiognomy. Results from herpetofauna trapping demonstrated that Scaphiopus couchii, a fossorial anuran, occupy Prosopis sites at a much higher rate than at Tamarix sites, which were almost completely avoided. S. couchii was also found to be closely tied to xero-riparian habitat components present at Prosopis sites and soil analyses indicate that aspects of soil moisture and texture play an important role in the partitioning of this species across altered riparian habitats. Lizard abundance was found to be significantly lower in Tamarix habitat, with the majority of captures attributed to the generalist whiptail Aspidoscelis tigris. Additionally, more than half of lizard species that were analyzed displayed a negative association to Tamarix habitat. Of the three habitat types considered, Populus-Salix supported the greatest abundance of lizards. Based on this study, the deleterious effects of xerfication on a riparian herpetofauna community may be lesser than those of Tamarix invasion. These two forms of riparian habitat shift often co-occur, with the ultimate cause being changes in hydrologic regime. This may imply that a bottom-up approach, wherein historic hydrology is restored to restore or maintain native habitats, to riverine management is appropriate for riparian herpetofauna conservation. / Dissertation/Thesis / Masters Thesis Applied Biological Sciences 2018

Diorhabda elongata elongata leaf beetles were released at two field locations in the upper Colorado River watershed of Texas in 2003 and 2004 for the biological control of invasive Tamarix, exotic trees deteriorating riparian ecosystems of western North America. Establishment and biological success were monitored using trees on transects from the release points. D. elongata elongata released at the Lake Thomas site in August 2003 successfully overwintered and were recovered in the spring 2004; however, beetles were not present after June 2004. The April 2004 release at Beals Creek led to establishment and survival during 2005 and 2006. Mean abundance increased from less than five insects per tree per 2 minute count in August 2004 to more than 40 insects per tree per 2 minute count in August 2006. By then the population was dispersed throughout an area of approximately 12 hectares and beetles were present on 100% of the 47 trees surveyed, 57% of which were at least 90% defoliated. To measure the impact of beetle defoliation on Tamarix, nonstructural carbohydrates (NCHOs) were measured in manipulative field cage experiments in Texas and natural experiments in Nevada. There was no significant difference in NCHOs between trees with versus trees without beetle herbivory in the cage experiment, although spring foliage regrowth was reduced by 35% in trees defoliated the previous fall. In Nevada, root crown tissue was sampled in 2005 and 2006 from trees that had experienced 0-4 years of defoliation. In 2005, NCHO concentrations differed between tree stands and ranged from 9.0 ± 0.8% (Mean ± SE) in non-defoliated trees to 3.2 ± 0.4%, 2.1 ± 0.4% and 2.3 ± 0.4% in trees defoliated for 1, 2 and 3 successive years, respectively. NCHO concentrations in 2006 were similar, ranging from 13.6 ± 0.9% in non-defoliated trees to 7.6 ± 0.8%, 2.3 ± 0.4%, 1.5 ± 0.3% and 1.7 ± 0.4% in trees defoliated for 1, 2, 3 and 4 years, respectively. The establishment, biological success and host impact of D. elongata leaf beetles suggest there is potential for biological control of Tamarix in the United States.