Defoliation effects of Diorhabda carinulata on tamarisk evapotranspiration and groundwater levels

Abstract

Diorhabda carinulata (northern tamarisk beetle) has been released in the western United States as a biological control agent for the invasive plant Tamarix spp. (tamarisk). A few studies have been conducted analysing the effects of beetle defoliation on tamarisk water consumption, but predefoliation and post‐defoliation comparison based on field data is scarce. The question of whether beetles substantially alter tamarisk water consumption is still open for discussion. In this study, an eddy covariance station and groundwater monitoring well were installed in a tamarisk stand along the Virgin River near Mesquite, NV, in 2010 to observe the impacts of tamarisk defoliation on evapotranspiration (ET) and groundwater levels. ET was calculated using the eddy covariance method and the White method and supported by Landsat remote sensing estimates. Data collected in 2010 established a baseline since the beetles arrived at the site in late 2010 and started feeding on foliage causing tamarisk trees to turn to brown during 2011. Repeated defoliations in 2011 and 2012 show that post‐defoliation ET values and magnitude of diurnal groundwater‐level fluctuations decreased compared with the predefoliation values. Estimated annual ET and annual average daily groundwater fluctuations were reduced by 18% and 35%, respectively. However, the magnitude of effects of defoliation was dependent on the growth stage of tamarisk at the time of defoliation. Also, ET recovered within a month as tamarisk established new leaves. Results from this study suggest that long‐term changes in ET are highly dependent on repeated defoliation occurrences over several years. Copyright © 2015 John Wiley & Sons, Ltd.

Reduced evapotranspiration from leaf beetle induced tamarisk defoliation in the Lower Virgin River using satellite‐based energy balance

“…For validation purposes, METRIC ET was compared with ground‐based ET estimates obtained by an eddy covariance flux station installed in tamarisk on the Lower Virgin River (Figure ) (Sueki et al, ). A polygon encompassing the approximate eddy covariance flux station footprint was used to spatially average METRIC ET estimates within the footprint at daily time steps (Figure ).…”

“…Yearly pre-beetle and post-beetle Lower Virgin ET versus ET r Average yearly ET results for the Lower Virgin and Lower Muddy River are presented in Comparison with eddy covariance flux station ET estimates For validation purposes, METRIC ET was compared with ground-based ET estimates obtained by an eddy covariance flux station installed in tamarisk on the Lower Virgin River (Figure 1) (Sueki et al, 2015). A polygon encompassing the approximate eddy covariance flux station footprint was used to spatially average METRIC ET estimates within the footprint at daily time steps (Figure 1).…”

Longer term effects of biological control on tamarisk evapotranspiration and carbon dioxide exchange

“…Our ET estimates for the five other sites were in rough agreement with previously published rates (Figure , Table ). Previous studies corroborate the use of NDVI for tamarisk stand vigour and water use (Bedford, Sankey, Sankey, Durning, & Ralston, ; Dennison et al, ; Everitt, Yang, Fletcher, Deloach, & Davis, ; Hultine et al, ; Meng et al, ; Nagler et al, ; Nagler et al, ; Sueki et al, ).…”

“…Previous, shorter term studies on several western U.S. rivers have all shown that beetle defoliation reduces plant transpiration temporarily (~2-8 weeks), then tamarisk regrows leaves and ET rates recover (Dennison et al, 2009;Hultine, Nagler, et al, 2010;Nagler et al, 2012;Snyder et al, 2012;Sueki et al, 2015). Our current study is unique in that 12 years of measurements were made, during a period when weather encompassed both extreme drought years and two very wet years (Figure 1 Our first hypothesis that beetles would produce a reduction in ET loss and CO 2 uptake, if beetle density remained high, was not supported.…”

“…This agrees with previous research findings indicating little possibility of sustained “water salvage” with tamarisk reduction in these environments where potential ET exceeds PPT and groundwater is bioavailable (Hultine, Belnap, et al, ; Hultine & Bush, ; Hultine, Nagler, et al, ; Nagler et al, ; Nagler et al, ; Owens & Moore, ). It also supports the general pattern found in many studies (Ji et al, ; Nagler et al, ; Nagler et al, ; Sueki et al, ) that the first 1 to 3 years of defoliation are most extreme, then beetles generally decline in density as they move on to search for greener tamarisk patches (Ji et al, ). For example, Nagler et al () used a combination of remotely sensed Landsat and MODIS greenness imagery over a 10‐year period to estimate ET for six sites in the Western United States: Lower Dolores River, Middle–Upper Dolores River, Humboldt River, Walker River, Upper Colorado River, and Bighorn River.…”