MODELING THE PHENOLOGY AND SPREAD OF TAMARIX BEETLE INFESTATION AND IMPACT ON WATER SAVINGS

We summarize preliminary findings of our assessment of phenology and water use (sap flux and satellite-derived evapotranspiration (ET) rates) in two adjacent stands of beetle-infested saltcedar (Tamarix Spp.) stands on the Dolores River, Utah, USA. A 10 m tower was erected in each stand prior to 2008. Beetle damage was measured using canopy cover from images taken from tower-mounted visible and infrared cameras (“phenocams”). Time-lapse image sets from the cameras were compared with fine-scale estimates of water use using stem sap flow measurements conducted over three growing seasons (2007-2009). Fractional cover from tower phenocams was comparable to cover from MODIS Enhanced Vegetation Index (EVI). Also, EVI was combined with meteorological data to estimate evapotranspiration (ET) at 15 release sites throughout the western USA. ET was estimated at 16-day intervals from 2000-2009, encompassing pre- and post-release periods at each site. Ground data included leaf area index (LAI) data from an LAI2000, canopy cover via camera, vegetation structure, composition, phenology, and litter traps. Preliminary results from the sap flux, phenocams and imagery show that both cover and plant transpiration fell dramatically during or shortly after the defoliated period, but recovered when new leaves were produced each year. Baseline ET rates were low, 2-6 mm d -1 in summer (<0.5 potential ET). At 4 of 15 sites, estimated ET by MODIS decreased markedly after release. At other sites, no decrease in ET was detected. ET tended to recover to pre-release levels at affected sites. Potential water salvage was constrained to the period of defoliation.