• Red Rocks with water in front of them in the desert.
  • Clouds behind Joshua Tree and bushes.
  • Desert flowers blooming in bushes in front of mountains in the desert.
  • Setting sun reflecting of clouds of orange and blue behind a joshua tree.
  • Hoover Dam intake towers with water behind the dam showing that it is not full.

2012 SCIENCE PROJECTS

From genotype to river basin: the combined impacts of climate change and biocontrol on a dominant riparian invasive tree/shrub (Tamarix spp.)

Science Need(s)

Impacts of climate change and land/resource management to watersheds and associated hydrecologic resources; Climate change impacts to surface water and groundwater dependent habitats and species; Climate change impacts to future water supply and resource availability for humans and ecosystems.

Grantee: Desert Botanical Garden
Principle Investigators: Kevin Hultine, Dan Bean, Tom Dudley, Shannon Fehlberg, Kevin Grady, Andrew Salywon
Cooperative Agreement: $151,911 in non-Federal funds and $149,269 in Federal funds provided by BOR
Project Duration: 2012-2014

Project Goal(s)

Test whether climate warming amplifies the deleterious impacts of herbivory by the tamarisk leaf beetle on tamarisk trees; test for an association between plant genotype and resistance to drought, herbivory, and/or the interaction of drought*herbivory; and determine whether expanding beetle populations display shifts in reproductive phenology that will facilitate their spread below Lake Mead, and enhance their impacts to tamarisk.

Brief Project Description

Delivering adequate water supplies to support expanding human enterprise while maintaining the necessary flow regimes to support desired riparian ecosystems and formally protected wildlife species that depend upon them is increasingly difficult in the arid western United States. Many riparian systems have undergone dramatic alteration over the last 50 - 100 years, exacerbating the conflicts between resource use and biodiversity protection. One of the most visible changes that is in part due to altered flow regimes is the establishment of invasive plant species in riparian ecosystems. The highest priority invasive riparian plant is the Eurasian tree/shrub, tamarisk (or saltcedar, Tamarix spp.) the third most abundant woody species in the western United States riparian zones. Tamarisk control and removal has become a priority of riparian ecosystem management, due in part to its potential negative impacts on stream flow and groundwater recharge.

A controversial and potentially effective tamarisk control approach is the release of the tamarisk leaf beetle, Diorhabda carinulata. The beetle has spread throughout virtually the entire upper Colorado River Basin, established major populations at Lake Mead in 2012, and is now poised to expand into the lower Colorado River Basin concordant with documented evolutionary change in beetle developmental that enables southern establishment. The beetle feeds exclusively on tamarisk, resulting in periods of defoliation that can last several weeks. These episodic defoliation events result in carbon starvation that in turn reduces leaf production and growth, leading to incremental dieback and in some cases mortality. The actual rate of mortality, however, is highly variable across the landscape. Repeated years of defoliation can result in anywhere between 0% to 100% mortality, with mortality rates of 20-40% being common after three to five years. Superimposed on this direct plant/herbivore relationship is the potential impact of climate change on the future performance of tamarisk, and hence on its effects (both negative and positive) on ecosystem structure and function. Temperature- and drought-related mortality of native riparian tree species is not random and some genotypes are more susceptible than others. Common garden studies show that riparian species exhibit substantial genetic variation and source population differences in survival and growth in hotter and drier environments. Tamarisk shows a similar range of responses to environmental stressors, both within Tamarix species and across hybrids formed from multiple Tamarix species. Nevertheless, information on how tamarisk populations and genotypes will respond to a combination of episodic defoliation and climate change is lacking. Therefore, the overarching objectives of this project are to: 1) determine if climate warming coupled with herbivory by the tamarisk leaf beetle synergistically reduce the performance of tamarisk in western North America: 2) assess whether some tamarisk populations are more susceptible (in terms of canopy die back, above ground productivity and plant mortality) to the combination of climate change and herbivory than others: and )3 evaluate how genetic change in D. carinulata will enable southern colonization into the lower Colorado River Basin and extend phenology, thereby changing riparian vegetation in this critical region.

Project Location

Lower Colorado River Basin

Project Tasks

  • Test whether climate warming amplifies the deleterious impacts of herbivory by the tamarisk leaf beetle on tamarisk trees.
  • Test for an association between plant genotype and resistance to drought, herbivory, and/or the interaction of drought*herbivory.
  • Determine whether expanding beetle populations display shifts in reproductive phenology that will facilitate their spread below Lake Mead, and enhance their impacts to tamarisk.

Project Deliverables

  • All data will be imported into a project relational database, accompanied by relevant metadata files and backed up regularly following standard laboratory protocols.
  • Spatial maps of tamarisk hybrid introgression.
  • Spatial maps of predicted tamarisk beetle spread into the lower Colorado River Basin.
  • Gas exchange data - interval-based measurements of the photosynthesis rate, leaf conductance, and transpiration of tamarisk trees occurring in the experimental common garden.
  • Stable carbon isotope ratio data- interval-based measurements of the carbon isotope ratio values from tamarisk trees occurring in the experimental common garden.
  • Percent growth and biomass allocation of tamarisk genotypes - interval-based measurements from the common garden.
  • Percent mortality of tamarisk genotypes- interval based measurements of tamarisk mortality from the common garden, and monitoring sites on the Virgin River.
  • Microclimate data- continuous microclimate data from a weather station to be located at the common garden that will report air temperature, relative humidity, and sunlight intensity.
  • A series of research-specific methodological protocols for each of the laboratory and field research measurements to be collected
  • A detailed site description of tamarisk genotype locations and monitoring plots, including photographs

Documents Available for Download