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.

Saltcedar is an invasive shrub that has moved into western United States riparian areas and is continuing to spread. Saltcedar is a phreatophyte that can utilize a saturated water table for moisture once established and is also highly tolerant of saline soil and water conditions. Literature has indicated that depth to the water table and salinity have a significant effect on growth and water use by saltcedar. Several studies were initiated to help develop a simulation model of saltcedar growth and water use based on the EPIC9200 simulation model. A study was initiated at the USDA-ARS Blackland Research Center Temple, Texas in the summer of 2002 to better understand the effects of water table depth and salinity on (1) saltcedar above and below ground biomass, root distribution, leaf area and (2) water use. Five different salinity levels (ranging from 0 ppm to 7500 ppm) and three different water table depths (0.5m, 1.0m, and 1.75m) were studied. Results indicated that increasing depth to the water table decreased saltcedar water use and growth. For the 0.5m water table depth, saltcedar water use during the 2002 growing season averaged 92.7 ml d-1 while the 1.75m depth averaged 56.6 ml d-1. Both root and shoot growth were depressed by increasing water table depth. Salinity had no effect on saltcedar growth or water use except at the 1250 ppm level, which used 110 ml of H2O d-1. This salinity had the highest water use indicating that this may be near the ecological optimum level of salinity for saltcedar. A predictive equation was developed for saltcedar water use using climatic data for that day, the previous day's climatic data, water table depth and salinity that included: previous day total amount of solar radiation, water table depth, previous day average wind speed, salinity, previous day total precipitation, previous day average vapor pressure, minimum relative humidity, previous day average wind direction, and maximum air temperature. Data from the field study and a potential growth study were integrated into the model. The model was parameterized for the Pecos River near Mentone, Texas. Predicted saltcedar water use was slightly lower than results reported by White et al. 2003.

Western riparian zones have undergone significant landscape changes over the past several decades, with introduced saltcedar (Tamarix spp.) as a crucial component of this transformation. Saltcedar, now a dominating presence along many western rivers, due to its high tolerance to drought, salinity and stress, is considered to be a high-water-use plant that can desiccate disturbed river systems. Where native and saltcedar plant communities occur together, it is important to understand water use patterns and the physiological responses of each species to environmental stress factors, as a way to project an eventual course of succession processes and management options at a given site. Stress and disturbance in the form of reduced stream flows and land use changes may influence these interactions. Understanding the conditions that allow for saltcedar dominance is critical in determining riparian water budgets, and developing effective management strategies. Sap flux sensors were used to measure the physiological response of co-occurring communities of saltcedar and native trees to these environmental stress factors during the pre-monsoon period in early summer, a time of maximum stress for riparian vegetation. The results suggest that native trees are still competitive with salt cedar so that a mixed plant community is likely to continue on the San Pedro River on the condition that current groundwater levels and river flows are maintained. If base flows and depth to groundwater continue to decline, this competitive balance between saltcedar and native trees likely could change.

The invasive species Saltcedar is affecting water and land resources throughout the western states of America. Because of great water use capabilities and other ecosystem detriments, Saltcedar has been targeted for treatment. For successful management of Saltcedar, individual landowners need to be aware of the costs and benefits of treating Saltcedar. Eleven of the most commonly reported treatment methods were evaluated for firm level economic feasibility. Evaluated on the basis of treatment cost, treatment effectiveness, Saltcedar water-use, and re-vegetation water-use, a production plan of ten years was created for each treatment method. Some treatment methods required re-treatment and were evaluated with re-treatments most commonly found in the literature. Of the treatment methods evaluated, five treatment methods were determined to be most feasible. Landowner valuation of environmental changes in the ecosystem brought on by Saltcedar is very important in the decision of which treatment method to implement. Personal valuation, over a period of ten years, will often determine which treatment methods are most cost efficient.

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