Introduction: Tamarisk (Tamarix spp., also saltcedar) is a non-native tree introduced to the United States during the 19th century as an ornamental species and solution to erosion in the American West (Robinson 1965). Tamarisk can form dense monotypic stands, which have been linked to a decline in richness and diversity of native plants (Engel-Wilson & Ohmart 1978; Lovich et al. 1994) and wildlife (Anderson et al. 1977; Durst et al. 2008) in riparian areas. As a result, natural resource managers have invested millions of dollars to control tamarisk (Shafroth & Briggs 2008). Few studies have conducted community-level analyses to document the impact of one of these methods, the introduction of a native enemy or predator, such as a biocontrol agent.
Amphibians, reptiles, and birds are consumers within a riparian food web and can provide a tool to evaluate how biocontrol establishment and defoliation of tamarisk can impact ecosystem-level changes. For example along the Virgin River, biocontrol has increased solar radiation, reduced foliar canopy cover, and increased temperatures (Bateman et al. 2013a; Nagler et al. 2014) that could impact vertebrate species utilizing defoliated tamarisk stands. For example, many species of birds have been documented to breed in tamarisk habitats within the western United States (Sogge et al., 2008) including the endangered Southwestern willow flycatcher (Empidonax traillii extimus; Durst et al. 2007; USFWS 2002). Paxton et al. (2011) suggest that tamarisk defoliation may increase rates of nest predation or abandonment by birds breeding in tamarisk. Also, the increased temperatures in defoliated tamarisk stands may exceed critical limits of some avian embryos (Webb 1987). Ectothermic vertebrate species also respond to structural changes in their habitat (Pianka 1966). For example, species such as whiptail lizards (Aspidoscelis spp.) shuttle between microhabitats to maintain high body temperatures with fine precision (Bowker & Johnson 1980). The common side-blotched lizard (Uta stansburiana) selects habitats having a more open vegetation structure and population parameters tend to be negatively correlated with vegetation canopy cover (Nielsen & Bateman 2013). However, high temperatures in arid ecosystems can also exceed the thermal maximum of ectotherms. It is possible some reptiles may benefit from increased temperatures and solar radiation; whereas, others may avoid areas where they might overheat.
This product was co-funded by multiple Landscape Conservation Cooperatives: Desert LCC and the Southern Rockies LCC.
