Ecohydrological consequences of saltcedar beetle-induced tamarisk defoliation
The presence of tamarisk in western North America has had considerable consequences on
water resources including driving a reduction in water availability for both human enterprise
and biodiversity (Busch and Smith 1995, Stromberg 1998, Pataki et al. 2005). Changes in
streamflow via tamarisk water consumption have measurable impacts on down-stream water
appropriations and tamarisk species control has become an important aspect of local, state
and federal government efforts to manage public and private lands. Eradication and restoration
efforts are currently ongoing along many riparian corridors, but attempts to eradicate tamarisk
have had variable success. Traditional control strategies such as mechanical removal, fire
and herbicide treatments have often proven costly, unsuccessful, or have had unintended
negative ecological impacts. An alternative biological control program was developed
to control the spread of tamarisk. In 1996, the USDA - Animal and Plant Health Inspection
Service (APHIS), approved the saltcedar leaf beetle (Diorhabda elongata Brulle) from central
Asia for release (Dudley 2005). Diorhabda feeds selectively on tamarisk in the larval and
adult stages, and pupation and adult over-wintering takes place in the litter beneath tamarisk
shrubs.
In the summer of 2004, APHIS orchestrated the release of several thousand saltcedar leaf
beetles at multiple locations along the Colorado River. The goal of the beetle release was to
facilitate an aggressive long-term eradication and restoration program in eastern Utah. The
beetle has shown considerable success locally in defoliating tamarisk and in some cases has
traveled several km from the release points. However, neither local, state nor federal agencies
have coordinated a comprehensive monitoring program to assess beetle impact on tamarisk habitat
or water resources within the Colorado Plateau region. Moreover, there are currently no data
to assess whether beetle-induced tamarisk defoliation translates into widespread mortality.
The newly established, University of Utah, Entrada Field Station provides an ideal opportunity to investigate the hydrologic and ecologic consequences of
beetle-induced tamarisk defoliation and mortality. As of fall of 2006, the saltcedar beetle
traveled to within 10-river km downstream of the field station before entering winter
dormancy. Current projections have the beetle moving through the field station by spring of
2008, or possibly sooner. We will exploit the local beetle release to ask the following
questions: will partial or total defoliation result in measurable long-term changes in
evapotranspiration fluxes, stream flow and groundwater discharge? Will defoliation lead to
widespread mortality? Tamarisk transpiration studies are currently ongoing (See Figures), and
we will soon begin collecting comprehensive data on streamflow patterns, groundwater discharge
and soil moisture in response to beetle-induced changes in tamarisk activity.
Tamarisk Sapflow |
Tamarisk Sapflow Sensor |
Tamarisk Sapflow Station |
Literature Cited
Busch, D.E. and Smith, S.D. (1995) "Mechanisms associated with decline of woody species in
riparian ecosystems of the southwestern U.S." Ecological Monographs 65:347-370
Dudley, T.L. (2005) "Progress and pitfalls in the biological control of saltcedar
(Tamarix spp.) in North America" Proceedings of the 16th U.S. Department of Agriculture
interagency research forum on gypsy moth and other invasive species GTR-NE-337
Pataki, D.E., Bush, S.E., Gardner, P., Solomon, D.K., and Ehleringer, J.R. (2005) "Ecohydrology
in a Colorado River riparian forest: implications for the decline of Populus Fremontii" Ecological Applications 15:1009-1018
Stromberg, J. (1998) "Functional equivalency of saltcedar (Tamarix chinensis) and Fremont
cottonwood (Populus fremontii) along a free flowing river" Wetlands 18:675-686
