Methods for Measuring Tamarisk (Tamarix spp.) Water Use on Two Sub-Watersheds in The Western United States as Impacted by The Tamarisk Leaf Beetle (Diorhabda spp.)

The Dolores River in Utah and the Virgin River in Nevada are ecosystems under pressure from increased groundwater withdrawal due to growing human populations, climate change and introduced species such as Tamarix spp. (tamarisk). Tamarisk is reputed to take excessive water from its environment. Controlling tamarisk is of concern in the western United States where plants grow quickly in already fragile and diminishing riparian areas. For this reason, biologic control beetles Chrysomelidae: Diorhabda carinulata were released to weaken the tamarisk population, thus reducing its water use. The studies for this dissertation were conducted between 2010 and 2011. We quantified tamarisk water use over multiple cycles of annual defoliation using sap flow measurements, leaf area index (LAI), well data, allometry and satellite imagery from EOS-1 Moderate Resolution Imaging Spectrometer (MODIS) sensor. Study objectives for the Virgin River were to measure evapotranspiration (ET) before beetles ever arrived and to examine the effects on tamarisk ET in the year after beetle arrival. This site showed plant ET from sap flow averaged about 4.3 mm m⁻² leaf day⁻¹ in 2010. In 2011, ET from sap flow averaged 6.4 mm m⁻² leaf area day⁻¹ pre beetle arrival, but dropped to 3-4 mm m⁻² leaf area day⁻¹ after beetle arrival. Stand level ET measured by MODIS was 2.2 mm d⁻¹ in 2010 and approximately 1.5 mm day⁻¹ when beetle arrival was measured in 2011. Significant visual change was apparent as the trees senesced. Results showed the first year of beetle arrival resulted in reduced ET but did not result in significant water savings. We also compared the reaction of the newly defoliated (in 2011) Virgin River site to the long-term defoliated (since 2007) Dolores River site to explore if all beetle invasions were created equal. This paper views the two sites as fairly extreme examples of tamarisk stand reaction to the beetle. While no mortality was reported at the Dolores River site, the site is much older, less photosynthetically active and covers far less ground when compared to the younger tamarisk monoculture on the Virgin River. Pre-beetle arrival Normalized Difference Vegetation Index (NDVI) values were higher on the Virgin River than on the Dolores River. Beetle arrival at each site was captured with Landsat NDVI and a reduced NDVI signal (13% drop in NDVI at Dolores River, 5% drop at Virgin River) was seen after beetle arrival.Release 06-Oct-201

Rapid dispersal of saltcedar ( Tamarix spp.) biocontrol beetles ( Diorhabda carinulata ) on a desert river detected by phenocams, MODIS imagery and ground observations

We measured the rate of dispersal of saltcedar leaf beetles (Diorhabda carinulata), a defoliating insect released on western rivers to control saltcedar shrubs (Tamarix spp.), on a 63km reach of the Virgin River, U.S. Dispersal was measured by satellite imagery, ground surveys and phenocams. Pixels from the Moderate Resolution Imaging Spectrometer (MODIS) sensors on the Terra satellite showed a sharp drop in NDVI in midsummer followed by recovery, correlated with defoliation events as revealed in networked digital camera images and ground surveys. Ground surveys and MODIS imagery showed that beetle damage progressed downstream at a rate of about 25kmyr-1 in 2010 and 2011, producing a 50% reduction in saltcedar leaf area index and evapotranspiration by 2012, as estimated by algorithms based on MODIS Enhanced Vegetation Index values and local meteorological data for Mesquite, Nevada. This reduction is the equivalent of 10.4% of mean annual river flows on this river reach. Our results confirm other observations that saltcedar beetles are dispersing much faster than originally predicted in pre-release biological assessments, presenting new challenges and opportunities for land, water and wildlife managers on western rivers. Despite relatively coarse resolution (250m) and gridding artifacts, single MODIS pixels can be useful in tracking the effects of defoliating insects in riparian corridors