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

Authors: Snyder, Keirith; Scott, Russell - Russ

Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/2019
Publication Date: 11/16/2019
Citation: Snyder, K.A., Scott, R.L. 2019. Longer term effects of biological control on tamarisk evapotranspiration and carbon dioxide exchange. Hydrological Processes. 34(2):223-236. https://doi.org/10.1002/hyp.13639.
DOI: https://doi.org/10.1002/hyp.13639

Interpretive Summary: Biological control of Tamarix spp. (Tamarisk) with Diorhabda spp. (tamarisk beetle) was initiated in several states in the western United States in 2001. We analyzed a 12-years of data on net carbon dioxide exchange, evapotranspiration, beetle abundance and 15 years of satellite greenness from a tamarisk-invaded site in western Nevada along the Truckee River. Diorhabda carinulata (northern tamarisk beetle) appeared at the site in 2007. Large beetle outbreaks and associated defoliation of the tamarisk occurred in 2008 and 2009, then the beetle population was highly variable from year to year. Since 2016 the beetle population declined through time. Total evapotranspiration (ET) noticeably declined from direct beetle herbivory in 2008, 2009 and 2010, but the decline in ET was transient as trees regrew leaves. In 2012 and 2013 total ET was low likely from the combined effects of drought and beetle herbivory pressure. Total ET losses were primarily driven by annual precipitation with the greatest ET in “wet” years, and reduced ET when precipitation fell below 100 mm. ET and photosynthesis were highly correlated to NDVI (r2 = 0.91). We used this relationship to estimate growing season ET from Landsat NDVI for tamarisk sites across several southwestern USA rivers. There was a remarkable coherence of estimated ET and measured ET between the cold desert Truckee River site and sites along the Dolores, upper Rio Grande, and Virgin Rivers. In the 2005 through 2018 analysis period, ET declined after beetle arrival, but nearly all sites showed a partial or complete recovery in ET in subsequent years. Since 2010, no further releases of the beetles have occurred due to wildlife concerns, and subsequent declines in beetle populations eliminated the “outbreak” conditions apparently required to impair Tamarisk physiological function and significantly reduce ET.

Technical Abstract: Biological control of Tamarix spp. (tamarisk) with Diorhabda spp. (tamarisk beetle) was initiated in several states in the Western United States in 2001. We analyzed 12 years of evapotranspiration (ET), net ecosystem production (NEP), and beetle abundance data from a tamarisk-invaded site in Western Nevada along the Truckee River. Diorhabda carinulata (northern tamarisk beetle) appeared at the site in 2007. Large beetle outbreaks and associated defoliation of the tamarisk occurred in 2008 and2009, then the beetle population was highly variable from year to year. Since 2016, the beetle population declined. Growing season ET noticeably declined from direct beetle herbivory in 2008, 2009, and 2010, but the decline in ET was seasonally transient as trees regrew leaves. In 2012 and 2013, total growing season ET was low, likely due to the combined effects of drought and beetle herbivory pressure. Total seasonal ET losses and NEP were primarily driven by annual precipitation with higher values in wetter years and reduced values when precipitation fell below 100 mm. In the last 2 years of the study, 2017–2018, there were few to no beetles observed at the site, and we measured increased tamarisk leaf area index, ET, and NEP. Since2010 at the study site, no further releases of the beetles have occurred due to wild-life concerns, and subsequent declines in beetle populations where such that the “outbreak” conditions apparently required to impair tamarisk physiological function and significantly reduce ET have not occurred. ET and photosynthesis were highly correlated (r2= .91) to the Landsat-satellite normalized difference vegetation index (NDVI). Using a relationship between growing season ET and NDVI, we estimated ET for five additional tamarisk sites along several southwestern U.S. rivers. In the 2005to 2018 analysis period, NDVI-estimated ET declined at all sites after beetle arrival with three sites showing a recovery in pre-beetle ET rates in subsequent years. At the other three sites, ET rates have not recovered to pre-beetle levels.Biological control of Tamarix spp. (tamarisk) with Diorhabda spp. (tamarisk beetle) was initiated in several states in the Western United States in 2001. We analyzed 12 years of evapotranspiration (ET), net ecosystem production (NEP), and beetle abundance data from a tamarisk-invaded site in Western Nevada along the Truckee River. Diorhabda carinulata (northern tamarisk beetle) appeared at the site in 2007. Large beetle outbreaks and associated defoliation of the tamarisk occurred in 2008 and2009, then the beetle population was highly variable from year to year. Since 2016, the beetle population declined. Growing season ET noticeably declined from direct beetle herbivory in 2008, 2009, and 2010, but the decline in ET was seasonally transient as trees regrew leaves. In 2012 and 2013, total growing season ET was low, likely due to the combined effects of drought and beetle herbivory pressure. Total seasonal ET losses and NEP were primarily driven by annual precipitation with higher values in wetter years and reduced values when precipitation fell below 100 mm. In the last 2 years of the study, 2017–2018, there were few to no beetles observed at the site, and we measured increased tamarisk leaf area index, ET, and NEP. Since2010 at the study site, no further releases of the beetles have occurred due to wild-life concerns, and subsequent declines in beetle populations where such that the “outbreak” conditions apparently required to impair tamarisk physiological function and significantly reduce ET have not occurred. ET and photosynthesis were highly correlated (r2= .91) to the Landsat-satellite normalized difference vegetation index (NDVI). Using a relationship between growing season ET and NDVI, we estimated ET for five additional tamarisk sites along several southwestern U.S. rivers. In the 2005to 2018 ana